Class 11 Medical Chemistry - Hydrogen

State three uses of water vapour in the air.

The three uses of water vapour in the air:

$\rightarrow$ Water vapour plays a dominant role in the radiative balance and the hydrological cycle.

$\rightarrow$ It is the principle element in the thermodynamics of the atmosphere, it transports latent heat, it contributes to absorption and emission in a number of bands and it condenses into clouds that reflect and absorb solar radiation, thus directly affecting the energy balance.

$\rightarrow$ In the lower atmosphere, the water vapour concentrations can vary by orders of magnitude from place to place. This variability creates a fundamental problem in climate modelling due to be high temporal and spatial resolution needed to resolve all processes.

How would you confirm that a colourless liquid given to you is pure water? $(AS_1)$

If the boiling point and freezing point of the given liquid comes out to be

$100 ℃$ or

$373 K$ and

$0 ℃$ or

$273 K$ respectively under

$1 \text{ atm}$ pressure, it confirms that the given liquid is pure water.

Molecular mass of water is _______ a.m.u.

Molecular formula of water is

$H_2O$

So the molecular mass is

$2\times1(hydroen)+1\times16(oxygen)=18$

So the molecular mass of water is

$18a.m.u$

Name three metals which do not react with water, under normal conditions.

Gold and silver cannot react with water and also magnesium cannot react with water in normal condition it react with water steam.

Water exists in a liquid state over a wide range of temperature $0^o$ C to $100^o$ C. Explain.

Because it has the high specific heat value. so it takes more time to get heat or cool.

What is the chemical composition of water? Give its molecular formula.

The constituents of water are hydrogen and oxygen. The molecular formula is

$H_{2}O$ .

What is the difference between $2H$ or $H_{2}$ .

$\textbf{Explanation :}$

$H_2$ is a molecule. When two atoms of hydrogen combine together with a single bond, they form molecular hydrogen.

But,

$2H$ is actually two atoms of hydrogen in elemental form. These two hydrogen atoms are not bonded with each other through any kind of bond.

$\textbf{Additional information :}$ Hydrogen is the lightest element with atomic number

$1 AMU$ . Molecular hydrogen is a colorless, odorless, tasteless, and highly flammable gas.

In which group hydrogen is placed on the basis of electronic configuration?

The electronic configuration of hydrogen is

$1s^{1}$ . On this basis, hydrogen is placed in group

$1$ .

$H_{2}O_{2}$ solutions are stored in dark-colored plastic or wax-coated glass vessels often with negative catalysts such as urea or sodium stannate added as stabilizers.

State whether the given reaction is True or False?

The given statement given is

$True$ .

Usually,

$H_2O_2$ is easily reduced. So it is stored in dark coloured bottle which can prevent the auto-oxidation of

$H_{2}O_{2}$ by light.

Urea and sodium stannate act as a negative catalyst for the decomposition of

$H_{2}O_{2}$ .

Therefore the statement is true.

As many as _________ different combination of water are possible from $_1H^1, _1H^2, _1H^3$ and $_8O^{16}, _8O^{17}$ and $_8O^{18}$ .

There are

$n=3$ different hydrogen isotopes to choose from, and we have to choose

$r=2$ of them.

Therefore,

${^{n+r-1}{C}_{r}} = {^{2 + 3 - 1}{C}_{2}} = {^{4}{C}_{2}} = 6$

Also we have

$3$ different oxygen.

Therefore,

Total no. of different combinations of water

$= 6 \times 3 = 18$

Which gas is usually liberated when an acid reacts with a metal ?

'Hydrogen gas' is liberated when an acid reacts with a metal.

For example, Zinc reacts with dilute sulphuric acid to form zinc sulphate along with the evolution of hydrogen gas.

$Zn + H_2SO_4 \to ZnSO_4 + H_2$

Hydrogen ignites with a 'pop' sound when placed near a glowing splint (test for hydrogen gas).

Give the properties of water responsible for controlling the temperature of our body.

Hydration is necessary for human beings. There are many functions of water in our body.

1. Water is a carrier distributing nutrients to cells.

2. Water removes waste products like toxins from the body.

3. Water helps in the biochemical breakdown of nutrients.

4. Water has a large heat capacity which helps limit changes in body temperature in a warm or cold environment. Water allows the body to release heat when the temperature is higher than body temperature. The body begins to sweat and the evaporation of water from the skin surface very efficiently cools the body.

________ is oxidation number of hydrogen in NaH.

$\begin{array}{l}\text { Let } x \text { be the Oxidation state of 'H' } \text { by oxidation state rule.}\end{array}$

$\begin{aligned}x+1 &=0 \quad \text { (Sodium has }+1^{} \text { Oxidation state }) \\x &=-1\end{aligned}$

$\text { Therefore, -1 is oxidation number of Hydrogen in NaH. }$

Explain the resemblance of hydrogen to the other members of its group.

Hydrogen is the first element of the periodic table. Its atomic number is 1 with one electron. This electron is present in its first shell. Hydrogen resembles both alkali metals as well as halogens therefore its position is said to be anomalous. Properties of hydrogen resembling alkali metals-

1. Electronic configuration

2. Valency

3. Metallic character

4. Reducing agent

5. Combination with non metals.

The properties of water are different from the properties of the elements of which it is formed. Discuss.

Water is a compound made up of two elements hydrogen and oxygen. The characteristic properties of these elements are different from those of water, however hydrogen and oxygen have some common properties. They are both colorless and odorless gases.

What is the effect on litmus if it is introduced in pure water ?

Litmus paper does not show any color change in pure water as it has neutral pH which has value 7 and litmus show color change in both acidic and basic solution.

Which property of water enables it to modify the climate ?

Due to the high specific heat capacity, the presence of a large amount of water is able to modify the climate.

What is the composition of water? In what volume are its two constituent combined?

Water is a compound which forms whenever two or more atoms atoms form chemical bonds with each other. The chemical formula for water is

$H_2O$ which means each molecule of water consists of one oxygen atom chemically bonded to two hydrogen atoms.

State the position of hydrogen in the periodic table.

Comment on the dual position of hydrogen in the periodic table

Why is aluminium metal not used in the lab preparation of hydrogen?

Due to its highly negative redox potential,

$Al$ should react readily with water producing hydrogen gas but practically Al is passivated by formation of highly adhering surface film of aluminium oxide when

$Al$ metal is oxidised and this interferes with the

$Al$ water reaction at the surface of metal.

Hydrogen is collected by downward displacement of water and not of air, even though it is lighter than air. Explain why?

Hydrogen gas is almost insoluble in water,it can be collected by displacement of water using an inverted apparatus. Hydrogen is highly explosive when mixed with air.

What is the physical state of water at $257^0C$ ?

Water boils at

$100^0 C$ and converts from liquid state to gaseous state(vapor form) by latent heat of vaporization. Hence, water is in gaseous state at

$257^0C$ .

Why does ice float on water ?

The density of water is approx. one gram per cubic centimeter. It is dependent on its temperature but the relation is not linear. When cooled from room temperature liquid water becomes dense but at 4 degree Celsius pure water reaches its maximum density. As it is cooled it expands to become less dense. So the layer of ice floats on water as insulating layer. The warm layer settles at the bottom in winters.

$100^{\circ}C$ ?

Boiling point of water is

$100^0 C$ so water exist in both gaseous and liquid state at this temperature.

$0^{\circ}C$ ?

Both water and ice exist in this phase of equilibrium at

$0 ^0C$ . Ice and water are in equilibrium at this temperature. The melting of ice starts at zero degree celsius.

Explain why apparatus for laboratory preparation of hydrogen should be air tight and away from a naked flame?

Hydrogen gas is almost insoluble in water,it can be collected by displacement of water using an inverted apparatus. Hydrogen is highly explosive when mixed with air. Hydrogen is explosive when mixed with air so burns with explosion near the mouth of gas jar but burns out inside the jar because the burning requires the presence of oxygen which in not present inside the jar.

Why is sodium metal not used in the lab preparation of hydrogen?

Sodium is very reactive in nature and readily forms its hydroxide in the presence of air and moisture and can not be used to form hydrogen.

Deionised water is obtained in ion exchange method.
If this is true enter 1, if false enter 0.

Deionization (DI) is a water filtration process whereby total dissolved solids (TDS) are removed from water through ion exchange. In simple terms, by controlling the electric charge of ions in the water, it is possible to remove the TDS.

Thus, $H_2S$ becomes $D_2S$ .
If this is true enter 1, if false enter 0.

In exchange process, $H_2S$ gas is passed by successive bubbling through ice cold water and boiling water, a liquid containing about $2\%$ $D_2O$ is obtained which is then concentrated by fractional distillation and electrolysis. In the reaction, the hydrogen atoms in $H_2S$ exchange with deuterium from $D_2O$ present in water.

How can the production of dihydrogen, obtained from coal gasification, be increased?

Coal gasification method is used for the production of dihydrogen gas.
To increase the yield of dihydrogen, CO is reacted with steam in presence of iron chromate catalyst. This is water gas shift reaction. Carbon dioxide is scrubbed with solution of sodium arsenite.

$CO(g)+ H_2O (g) \rightarrow CO_2(g) + H_2(g)$

What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electron-rich compounds of hydrogen?

(i) Electron deficient compounds of hydrogen do not have sufficient number of electrons to form normal covalent bonds. Examples include hydrides of group 13 such as

$\displaystyle BH_3, AlH_3$ etc. They exist in polymeric forms such as

$\displaystyle B_2H_6, Al_2H_6$ . Thus, they make up their deficiency.

(ii) Electron precise compounds of hydrogen contain sufficient valence electrons to form covalent bonds. Examples include group 14 hydrides

$\displaystyle CH_4,SiH_4, GeH_4, SnH_4, PbH_4$ etc. These compounds have tetrahedral shape.

(iii) Electron rich compounds of hydrogen contain excess valence electrons to form covalent bonds.
Examples include group 15 and group 17 hydrides such as

$\displaystyle NH_3, PH_3, HCl, HBr$ etc. These compounds contains lone pairs of electrons.

What characteristics do you except from an electron-deficient hydride with respect to its structure and chemical reactions?

Electron deficient compounds of hydrogen do not have sufficient number of electrons to form normal covalent bonds. Examples include hydrides of group 13 such as

$\displaystyle BH_3, AlH_3$ etc.
They exist in polymeric forms such as

$\displaystyle B_2H_6, Al_2H_6$ . Thus, they make up their deficiency.
These compounds are electron acceptors (Lewis acids). They form complexes with Lewis bases.

$\displaystyle B_2H_6 + 2NMe_3 \rightarrow 2BH_3 \leftarrow NMe_3$

$\displaystyle B_2H_6+2CO \rightarrow 2BH_3 \leftarrow CO$

Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.

Hydrogen with atomic number 1 and electronic configuration

$1s^1$ is the first element in the periodic table. It resembles alkali metals as well as halogens. Hence, its position is anomalous. Some chemists argue that hydrogen should be placed along with alkali metals whereas other chemist argue that hydrogen should be placed with halogens.

Saline hydrides are known to react with water violently producing fire. Can $CO_2$ , a well known fire extinguisher, be used in this case? Explain.

Saline hydrides such as

$\displaystyle NaH,CaH_2$ violently react with water and form metal hydroxide and hydrogen gas.

$\displaystyle NaH(s) + H_2O(l) \rightarrow NaOH(aq) + H_2(g)$

$\displaystyle CaH_2(s) + 2H_2O(l) \rightarrow Ca(OH)_2(aq) +2H_2(g)$
During these reactions, large amount of energy is released so that hydrogen catches fire.

$\displaystyle CO_2$ cannot extinguish this fire as it is reduced by hot metal hydride.

$\displaystyle NaH+CO_2 \rightarrow HCOONa$
To extinguish this fire, sand (a highly stable solid) can be used.

Complete the following chemical reaction and classify into (a) hydrolysis, (b) redox and (c) hydration reaction.
$AlCl_3\, (g)\, +\, H_2O\, (l)\, \rightarrow$

The complete reaction is given below-

$\displaystyle AlCl_3(g) +3H_2O(l) \rightarrow Al(OH)_3(s) + 3HCl(aq)$

This is an example of hydrolysis reaction.

What do you understand by the term 'auto-protolysis' of water? What is its significance?

The reaction between two water molecules to produce hydronium ion and hydroxide ion is known as autoprotolysis of water. This is self ionization of water.

$\displaystyle 2H_2O \rightarrow H_3O^++OH^-$
This reaction indicates the amphoteric nature of water. It can act as an acid as well as a base. One water molecule donates electron whereas other water molecule accepts electron.

What do you understand by the term non-stoichiometric hydrides? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

In non stoichiometric hydrides, the ratio of the metal to hydrogen is fractional and does not correspond to actual formula. Their composition varies with temperature and pressure.

$\displaystyle TiH_x (x=1.8\ to\ 2)$ and

$\displaystyle ZrH_x(x=1.30\ to\ 1.75)$ are examples of non stoichiometric hydrides. d and f block elements form such types of hydrides.
Alkali metals readily lose their valence electron and act as strong reducing agents. The electrons lost by alkali metals are gained by H to form ionic hydrides in which the ratio of alkali metals to hydrogen is fixed. Hence, alkali metals form only stioichiometric hydrides.

Arrange the following.
(i) $CaH_2$ , $BeH_2$ and $TiH_2$ in order of increasing electrical conductance.
(ii) $LiH, NaH$ and $CsH$ in order of increasing ionic character.
(iii) $H-H, D-D$ and $F-F$ in order of increasing bond dissociation enthalpy.
(iv) $NaH, MgH_2$ and $H_2O$ in order of increasing reducing property.

(i) Ionic compounds conduct electricity whereas covalent compounds does not.

$\displaystyle BeH_2$ is a covalent hydride and does not conduct electricity.

$\displaystyle CaH_2$ is an ionic hydride and conducts electricity in molten state.

$\displaystyle TiH_2$ is metallic in nature and conducts electricity at room temperature.
Hence, the increasing order of electrical conductivity is

$\displaystyle BeH_2<CaH_2<TiH_2$ .

(ii) The ionic character of bond depends on electronegativity difference between two atoms. When the electronegativity difference is larger, the ionic character is smaller. On moving down the group of alkali metals, the electronegativity decreases from Li to Cs. Hence the ionic character increases in the order

$\displaystyle LiH < NaH < CsH$ .

(iii) Bond dissociation energy depends on bond strength. Bond strength depends on the attractive and repulsion forces present in a molecule.
Due to higher nuclear mass of

$\displaystyle D_2$ , the attraction between nucleus and bond pair in D-D is stronger than in H-H. This results in greater bond strength and higher bond dissociation enthalpy. Thus, the bond dissociation enthalpy of

$\displaystyle D-D$ is higher than that of

$\displaystyle H-H$ .
The bond dissociation enthalpy of F-F is minimum as the repulsion between the bond pair and lone pairs of F is strong.
Hence, the increasing order of bond dissociation enthalpy is

$\displaystyle F-F < H-H < D-D$ .

(iv) NaH is an ionic hydride and can easily donate its electrons. It is most reducing.

$\displaystyle MgH_2$ and

$\displaystyle H_2O$ are covalent hydrides.

$\displaystyle H_2O$ has lower reducing power than

$\displaystyle MgH_2$ as its bond dissociation energy is higher.

Hence, the increasing order of the reducing property is

$\displaystyle H_2O < MgH_2 < NaH$ .

Among $NH_3$ , $H_2O$ and $HF$ , which would you expect to have highest magnitude of hydrogen bonding and why?

The electronegativity of

$N, O$ and

$F$ is much higher than the electronegativity of

$H$ . Hence,

$\displaystyle NH_3, H_2O$ and

$HF$ forms hydrogen bonds.

$F$ is most electronegative and the magnitude of negative charge on

$F$ and positive charge on

$H$ is highest and thus, the

$H$ bonding is strongest in

$HF$ .

Complete the following chemical reaction and classify the into (a) hydrolysis, (b) redox and (c) hydration reactions.
$CaO\, (s)\, +\, H_2O\, (g)\, \rightarrow$

The complete chemical equation is given below.

$\displaystyle CaO(s)+H_2O(g) \rightarrow Ca(OH)_2 (aq)$

This is an example of hydration reaction. A molecule of water is added to

$CaO$ molecule.

How do you expect the metallic hydrides to be useful for hydrogen storage? Explain.

The metallic hydrides are useful for hydrogen storage. These metallic hydrides absorb hydrogen as H atoms. The metal lattice expands and becomes less stable. On heating, the metallic hydride decomposes to hydrogen and finely divided metal. The hydrogen obtained can be used as fuel.

Do you expect the carbon hydrides of the type $(C_nH_{2n\, +\, 2})$ to act as Lewis acid or base? Justify your answer.

These carbon hydrides are electron precise hydrides. They contain sufficient valence electrons to form covalent bonds.
They neither gain electrons nor lose electrons and hence, neither act as lewis acids nor act as lewis bases.

Compare the structures of $H_2O$ and $H_2O_2$ .

The central O atom in water is

$\displaystyle sp^3$ hybridized and two O-H bonds are present. Two lone pairs of electrons are present in two

$\displaystyle sp^3$ hybrid orbitals. Water molecule has bent geometry with H-O-H bond angle of

$\displaystyle 104.5^o$ . The structure of

$\displaystyle H_2O_2$ is non planar. A single covalent bond is present between 2 O atoms. Each O atom is covalently bonded to one H atom. Two O-H bonds are in different planes and the dihedral angle between the planes is

$\displaystyle 111.5^o$ in the gas phase.

What is the difference between the terms hydrolysis and hydration?

Hydrolysis is the reaction of salt and water to form acidic or basic solution.

$\displaystyle AcONa + H_2O \rightarrow AcOH +NaOH$

Hydration is the addition of water to ions or molecules.

$\displaystyle CuSO_4+5H_2O \rightarrow CuSO_4.5H_2O$

Explain syngas in detail.

A mixture of CO and hydrogen is known as syngas (synthesis gas or water gas). It is used for manufacturing methanol. It is produced by the action of steam on hydrocarbons or coke at high temperature in the presence of a catalyst.

$\displaystyle CH_4(g)+H_2O(g) \xrightarrow [Ni] {1270K} \underset {\text {Syngas}}{CO(g)+3H_2(g)}$

Complete the following chemical reaction and classify into (a) hydrolysis, (b) redox and (c) hydration reactions.
$Ca_3N_2\, (s)\, +\, H_2O\, (l)\, \rightarrow$

$\displaystyle Ca_3N_2(s) +6H_2O(l) \rightarrow 3Ca(OH)_2(aq)+2NH_3(aq)$

Hydrolysis is a chemical reaction in which water is used to break down the bonds of a particular substance.Hence this is a hydrolysis reaction.

Write chemical reactions to show the amphoteric nature of water.

Amphoteric nature of water is represented by following chemical reactions.
(1) Water as a base:

$\displaystyle H_2O(l)+H_2S(g) \rightleftharpoons H_3O^+(aq) + HS^-(aq)$
(2) Water as an acid:

$\displaystyle H_2O(l) + NH_3(aq) \rightleftharpoons OH^-+NH_4^+$
(3) Self ionization of water in which water simultaneous acts as acid and base.

$\displaystyle 2H_2O \rightarrow H_3O^+ + OH^-$

Describe the structure of the common form of ice.

Ice has crystalline structure which is highly ordered due to hydrogen bonding. It has hexagonal form at atmospheric pressure and cubic form at low temperature. Each O atom has tetrahedral geometry and is surrounded by 4 oxygen atoms each at a distance of 276 pm.

How aquatic animals survive is cold countries when temperature fall below $0^{\circ}C$ ?

Only the top layer of a lake or river freezes underneath the frozen upper layer, the water remains into its liquid form and does not freeze. Also, oxygen is trapped beneath the layer of ice. The anomalous expansion plays an important role by only freezing the upper layers in lake and rivers.

As oxygen is ______ soluble in water, air dissolved in water contains a higher percentage of oxygen ( $30 - 35$ %) than ordinary air ( $21$ %).

As oxygen is more soluble in water, air dissolved in water contains a higher percentage of oxygen (30−35%) than ordinary air (21%).

Pure water is a _______ conductor of electricity.

Pure water(distilled water) is a bad conductor of electricity. Because it is free from all the dissolved minerals which are metals and responsible for the conduction of electricity).

But the conductivity of water is due to the presence of impurities as metal carbonates and chlorides.

Match the Column-I with Column-II:

The boiling point of water:

$100^0C$

The freezing point of water:

$0^0C$

Anomalous expansion of water: Hydrogen bond is responsible for the anomalous expansion of water below

$4^0C$ .

The boiling point of an element or a substance is the temperature at which the vapour pressure of the liquid equals the environmental pressure surrounding the liquid

The higher the pressure, the higher boiling point of water. At lower the pressure, the boiling point of water decreases.Thus, the boiling point of water on hills (at high altitude, i.e. at low pressure) will become less than

$100^0C$

Hence, A-4, B-3, C-2 ,D-1

Magnesium reacts with steam to form and .

${ Mg }_{ \left( s \right) }+{ H }_{ 2 }{ O }_{ \left( l \right) }\longrightarrow { MgO }_{ \left( s \right) }+{ H }_{ 2\left( g \right) }$

Magnesium reacts with steam to form magnesium oxide and water.

As we go up the mountains, the boiling point of water decreases. Why?

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. On mountains atmospheric pressure decreases hence bp of water also decreases.

Water containing impurities doesn't freeze at $0$ . Explain?

The presence of impurities lowers (depresses) thefreezing point of a liquid. The impurities lower the vapour pressure of the solution so that ice can melt at a lower temperature.

Water bodies like sea, rivers etc., which are deep appear blue. Why?

When water is in small quantities it appear to be colorless, water's tint becomes a deeper blue as the thickness of the observed sample increases. The blue colour of deep water is an intrinsic property and is caused by the selective absorption and scattering of white light. Impurities dissolved or suspended in water may give water different colored appearances.

Water is tasteless, but we experience different tastes of water in different places. Why?

This is because of the varying concentration of the total dissolved minerals in the water .

When we see that the water is tasteless that's means we are talking about the pure water which don't have any taste. But the water we drink have the different amount of minerals and dissolved solids in it which impart the taste in water, and because different place water have different concentration of mineral so their taste also differ.

Moreover these mineral are important for human health also but upto a level that's why in a water in bottled we buy from market is known as mineral water. Also, each company mentioned the concentration of minerals on the mineral water bottle.

Write the uses of dihydrogen gas:

Uses of dihydrogen gas:
i. As a reactant in the production of ammonia by the Haber process.
ii. In the hydrogenation reaction of the preparation of vegetable ghee from vegetable oils.
iii. In welding metals.
iv. In oxyhydrogen flame for cutting metals.
v. In industrial production of methanol and hydrochloric acid.
vi. As rocket fuel.

Describe an experiment to prove that water is transparent.

Take a bowl/beaker half filled with water, place a lemon in the beaker of water. Keep it undistributed for few minutes in a place where there is enough light. Now, observe the immersed lemon from the top of the bowl/beaker. It is noticed that it is visible clearly from the top. Hence, this proves that water is transparent.

Explain the method of preparation of hydrogen gas in laboratory with chemical equation and diagram?

In the laboratory, dihydrogen gas is prepared by taking zinc granules in a

$500\ ml$ flask.
To this, dilute

$HCl$ or dilute sulphuric acid is added through a thistle funnel.
Dihydrogen gas is released and the gas is collected by the downward displacement of water because it is a gas lighter than water
Reaction:

$Zn_{(s)} + 2HCl_{(aq)} \rightarrow ZnCl_{2(aq)} + H_{2(g)}$

$Zn_{(s)} + H_{2}SO_{4(aq)} \rightarrow ZnSO_{4(aq)} + H_{2(g)}$ .

Excess of $KI$ and $dil. H_{2}SO_{4}$ were mixed in $50\ mL\ H_{2}O_{2}$ . The liberated $I_{2}$ required $20\ mL$ of $0.1\ N\ Na_{2}S_{2}O_{3}$ . Find out the strength of $H_{2}O_{2}$ in $g\ per\ litre$ .

$M_{eq}$ of

$H_2O_2$ =

$N\times 50$

$N\longrightarrow$ Normality of

$H_2O_2$

$M_{eq}$ of

$Na_2S_2O_3$ =

$0.1\times 20$

$\therefore$

$M_{eq}$ of

$H_2O_2$ =

$M_{eq}$ of

$Na_2S_2O_3$

$N\times 50=0.1\times 20$

$\therefore$

$N=0.04N$

$\therefore$ Volume strength of

$H_2O_2$ =

$N\times5.6$

$0.04\times 5.6$

$0.224g/L$

How many moles of $H_2O_2$ are present in 2 litres of 6.8% w/v $H_2O_2$ solution?

$6.8$ % (w/v)=

$\cfrac {6.8g\quad of\quad H_2O_2}{100ml\quad of\quad water}\times 100$

$\therefore$ In

$2$ litres,

$6.8\times 2\times 10g$ of

$H_2O_2$ will be present.

$\therefore$ Mass of

$H_2O_2=6.8\times 2\times 10=136g$

$\therefore$ Moles of

$H_2O_2=\cfrac {136}{34}=4$ moles

Calculate percentage of water of crystallization in : $Mg\ SO_7H_2O$ [Atomic masses of $Mg= 24, S=32, O=16, H=1]$

Molecular weight of water

$\displaystyle H_2O=2(1)+16=18$ g/mol.
Molecular weight of

$\displaystyle MgSO_4 \cdot 7H_2O =24+32+4(16)+7(18)=246$ g/mol
Percent of water of crystallisation in

$\displaystyle MgSO_4 \cdot 7 H_2O = \dfrac { 7 \times 18}{246} \times 100=51.2$ %.

Consider the reaction between Zn and dilute hydrochloric acid forming zinc chloride and liberating hydrogen.

The steps involved in balancing the given reaction by O.N. method are
(i) Write the skeletal equation involving all the known reactants and products.

$Zn+HCl\rightarrow ZnCl_2+H_2$
(ii) Indicate the O.N. of different atoms involved.

$\overset{0}{Zn}+\overset{+1}{H}\overset{-1}{Cl}\rightarrow \overset{+2}{Zn}\overset{-1}{Cl_2}+\overset{0}{H_2}$
(iii) Identify the elements which undergoes a change in O.N.

$\overset{0}{Zn}\rightarrow \overset{+2}{Zn}$ (O.N. increases)

$\overset{+1}{H}\rightarrow \overset{0}{H_2}$ (O.N. decreases)
(iv) Calculate the increase or decrease of O.N. per atom and multiply this number with the number of atoms which are undergoing the change.
(i)

$[\overset{0}{Zn}\rightarrow \overset{+2}{Zn}$

$2$ per atom

$]\times 1$
(ii)

$[\overset{+1}{H}\rightarrow \overset{0}{H_2}$

$1$ per atom

$]\times 2$
(v) Balance other atoms by simple method (if required)

$Zn+2HCl\rightarrow ZnCl_2+H_2$
This is the balanced equation.

Explain the method of preparation of hydrogen gas in laboratory with chemical equation and diagram.

In a conical flask, fitted with the delivery tube, few grams of granulated zinc is taken. Then dil.

$HCl$ is added. Zinc reacts with

$HCl$ to form zinc chloride and hydrogen gas.

$Zn+2HCl \to ZnCl_2+H_2 \uparrow$ .
The liberated hydrogen gas is collected in an inverted test tube placed in a water trough.

Why Hydrogen although lighter than air, is not collected by the downwards displacement of air?

Even though hydrogen is lighter than air it is not collected by downward displacement of air because of these reasons:

Hydrogen gets oxidised when it is exposed to oxygen which makes it burn with a pale blue flame and the residue is water. This means that it mixes with oxygen.

Downward displacement of air requires a gas that does not mix with air and is lighter than air. Hydrogen is lighter than air but mixes with air.

Why is Hydrogen placed in group $I$ of the modern periodic table ?

Hydrogen is placed in group

$I$ of the modern periodic table due to following reasons:-

$(1)$ It shows outer electronic configuration similar to group

$I$ elements (i.e.

$1s^{1}$ ).

$(2)$ It readily looses its electron to form

$H^{+}$ ion which resembles the electropositive character of group

$I$ elements.

$(3)$ It shows

$+1$ oxidation state like alkali i.e. group

$I$ elements.

$(4)$ Hydrogen also acts as a strong reducing agent like alkali metals and also forms binary compounds with electronegative elements which resembles the group

$I$ elements.

Why is distilled water considered to be the purest form of water?

Distilled water is water that has been boiled into vapor and condensed back into liquid in a separate container and this process is called distillation and condensed water obtained is called distilled water. Distilled water is free from all types of impurities so it is considered to be the purest form of water.

Why does water have higher boiling point than alcohol? At what temperature in kelvin, it can be change into solid state and into vapours?

Water has higher boiling point than alcohol because the extent of hydrogen bonding is stronger in water than in alcohol .
Moreover we know that water freezes into ice at 273 k and changes into vapour states at 373 K.

Why does hydrogen resemble both group $I$ and group $17$ elements ?

Hydrogen has electronic configuration of

$1s^{1}$ . It can accept the electron from metals to fulfill its' outer orbital like group

$17$ elements. On the other hand, it can donate its' electron to form

$H^{+}$ ion which is the characteristics of the group

$1$ elements.

Also, it has an electronic configuration like group

$1$ elements. On the other hand, it resembles group

$17$ elements as it shows higher ionization enthalpy like halogens.

In this way, hydrogen resembles both group

$1$ and group

$17$ elements.

Why ice is lighter than water?

When water freezes, water molecules form a crystalline structure maintained by hydrogen bonding. Solid water, or ice, is less dense than liquid water.
Ice is less dense than water because the orientation of hydrogen bonds causes molecules to push farther apart, which lowers the density.
Hence, Ice is lighter than water.

Water is a good fire extinguisher. But it is not used extinguish electrical fires and oil for?

Water is a good conductor of electricity. If we spray water on electric appliances during fire accident, it conducts electricity and gives us a shock.

Oil is less denser than water. In fire accidents due to oil, if we spray water, it will settle down due to more density and allow oil to fire continuously.

Explain the position of hydrogen in the periodic table on the basis of its electronic configuration.

Hydrogen is the first element of the periodic table & often called protium. Its electronic configuration is $[1s^1].$ Due to the presence of only one electron in its 1s shell, hydrogen exhibits a dual behaviour, i.e., it resembles both alkali metals and halogens.
As a result it is placed at the top of the alkali metals in group 1 & also along the halogens in group 17 since just like halogens,it also requires any one electron to have the configuration of the nearest noble gas element.

Physical properties of ice, water and steam are different. What is the chemical composition of water in all the three states?

Matter exists in tree forms and can be converted from one state to another. When state changes, only physical properties change but chemical composition remains same. So, chemical composition is

$H_2O$ only.

In order to decompose 9 g water 142.5 kJ heat is required. Hence, the enthalpy of formation of water is:

Decomposition of

$9g$ water

$= 142.5KJ$ heat required

Decomposition of

$18g$ water

$=x KJ$ heat required

$\therefore x = \dfrac{142.5\times 18}{9}$

$x = 285KJ$

Hence, the enthalpy of formation of water is

$-285KJ$

When water boils the temperature remains constant. Give reasons.

Water starts boiling at $100^oC$ temperature. After this temperature., the temperature of water becomes constant for some time even after the constant supply of heat.
Here the heat supplied is used to overcome the intermolecular force of attraction present in a water molecule to convert it into vapour.
This heat is known as latent heat of vaporization.
The change in temperature only takes place after conversion of water into vapour.

$2H_2$ is needed to make one molecule of water, here $'2H_2'$ means:

It takes two molecules of the diatomic hydrogen gas, combined with one molecule of the diatomic oxygen gas to produce two molecules of water. In other words the ratio of hydrogen to oxygen is 2:1, the ratio of hydrogen to water is 1:1, and the ratio of oxygen to water is 1:2.

How do you expect the metallic hydrides to be useful for hydrogen storage? Explain.

(1) The property of adsorption of hydrogen on tran-sition metals in metallic hydrides is widely used in catalystical reduction/hydrogenation reactions for the preparation of large number of compounds.

(2) Some of the metals like Pd, Pt can accommodate a very large volume of hydrogen and therefore, can be used as its storage media. This property has a high potential for hydrogen storage and as a source of energy.

Hydrogen is not a metal but it has been assigned aplace in the reactivity series of metals.Explain.

Despite not being a metal, hydrogen has been assigned a place in the reactivity series of metals because, hydrogen has a tendency to loose electrons and get converted to

$H^+$ ion which is similar to the property exhibited by metals

How can you prove that distilled water is a non-electrolyte? Explain with the help of well labelled diagram.

1346448_1137466_ans_cbb18f285e0048ebb9df8cfec7e93f2f.jpg

Explain the laboratory method for preparation of hydrogen peroxide.

Laboratory method of preparation of hydrogen peroxide.

(i)Acidifying

$BaO_2,8H_2O$ (barium peroxide)and removing excess water by evaporation under reduced pressure gives

$H_2O_2$

$BaO_2.8H_2O(s)+H_2SO_4(aq)\longrightarrow BaSO_4(s)+H_2O_2(aq)+8H_2O(l)$

(ii)peroxy disulphate,obtained by electrolitic oxidation of acidfeed sulphate solutions at high current density on hydrogens yields

$H_2O_2$ .

$2HSO_4^-(aq)\longrightarrow HO_3SOOSO_3H(aq)\longrightarrow 2HSO_4^-+2H^+(aq)+H_2O_2(aq)$

There are the

$2$ methods used for laboratory preparation of

$H_2O_2$ .

Among $PCl_3, CH_{3}^{+}, NH_{2}^{-}$ and $NF_3$ , ......... is least reactive towards water.

1308383_1235692_ans_e7f067aa111b452b8a6de422e6fba871.jpg

Answer the following:
(a) Name a process by which hydrogen gas is manufactured.
(b) Give equation for the reaction.
(c) How is hydrogen seperated from carbon dioxide and carbon monoxide?

(a) Commercially, hydrogen is prepared by Bosch process.
(b) (i) Steam is passed over hot coke at

$1000^\circ C$ in a furnace called converters. As a result water gas is produced which is a mixture of carbon monoxide and hydrogen gases.

$C+ H_20 \overset{1000^\circ C}{\longrightarrow} (CO+H_2) - Heat$

This reaction is endothermic in nature.
(ii) Water gas is mixed with excess of steam and passed over a catalyst ferric oxide

$(Fe_2O_3)$ and a promoter chromium trioxide

$(Cr_2O_3)$ .

$(CO+H_2) + H_2O \overset{Fe_2O_3/Cr_2O_3}{\underset{450^\circ C}{\longrightarrow}} CO_2+ 2H_2 + Heat$

This reaction is exothermic in nature.

c) (i) The products are hydrogen, carbon dioxide and some unreacted carbon monoxide. Hydrogen is separated from carbon dioxide by passing the mixture through water under pressure, in which carbon dioxide gets dissolved leaving behind hydrogen. Carbon dioxide can also be separated by passing it through caustic potash

$(KOH)$ solution.

$2KOH + CO_2 \longrightarrow K_2CO_3 +H_2O$

(ii) To separate carbon monoxide the gaseous mixture is passed through ammoniacal cuprous chloride in which carbon monoxide dissolves leaving behind hydrogen.

$CuCl +CO +2H_2O \longrightarrow CuCl.CO.2H_2O$

Thus hydrogen gas is obtained.

As many as...... different combination of water are possible form
$_{1}H^{1}, _{1}H^{2},_{1}H^{3}$ and $_{8}O^{16},_{8}O^{17},_{8}O^{18}$

1352686_1289008_ans_faffbd5191144b398bd7b80d96a7ae48.jpeg

Tripe point of water is

1328100_1312973_ans_b8dd8de9ac404bfab2ac900c62809f9c.jpg

What is the physical state of water at :
(a) $25^oC$
(b) $0^oC$
(c) $100^oC$ ?

(a)Water at

$25^o C$ is present in the liquid state.
(b) At

$0^oC$ , water can exist as both solid and liquid.
NOTE: At

$0^oC$ temperature, after getting the heat equal to the latent heat of fusion, the solid form of water i.e., ice starts changing into its liquid form i.e., water.
(c) At

$100^oC$ , water exists in liquid state at

$100^oC$ . At this stage, if we keep on supplying heat energy, water can change to gaseous state.

Wrte any two measures that you would suggest for the better management of water resources

1325869_1315698_ans_b77748ffd55f4092ac6a44d6b1bf6cde.jpg

Fill in the blanks :
............... is the purest form of natural water.

Rainwater is the purest form of natural water.

Fill in the blanks :
Water has .............. density and .............. volume at $4^0C$ .

1325878_1313484_ans_a8c62555efab4330ad84595ffa27e49f.png

Explain why $H_{2}$ and $O_{2}$ do not react at room temperature.

For this process a high temperature is needed which is not possible at room temperature.
Since no bond breaks to make an reacting atom, the reaction does not takes place at room temperature

These metal combines H to give white crystalline ionic hydrides of the general of the formula $MH$ .
The tendency to form their hydrides, basic character and stability decreases from Li to Cs since the electropositive character decreases from $Cs$ to $Li$ .

1351789_1274689_ans_d65b192b87d745e5931d1bf626620355.jpg

How hydrogen atom is different from atoms of all other element ?

1332879_1318133_ans_d486061f79784630810092ac5f7a46d2.jpg

What is potable water? Write its characters.

The water which is fit for drinking by human beings is called potable water.
Characteristics:

(i) It is transparent.

(ii) It is odourless and colourless.

(iii) It is harmless or free from disease causing bacteria.

Give reason to explain why it takes longer to dry wet clothes in humid weather?

In humid weather it takes longer time to dry wet clothes because the moisture and water vapour are present in humid weather they gets slight absorbed by the clothes and clothes maintain their wetness due to this they take a longer time to dry and in humid weather they don't get enough sunlight to dry themselves at a faster or normal rate, so they take a long time due to these reasons.

Water is liquid at room temperature but not hydrogen sulphide. Why?

Sulphur is less electronegative than oxygen, and the S-H bond is much less polar than the O-H bond. Hence, there is no hydrogen bonding in hydrogen sulphide, and it normally exists as a gas with discrete H2S molecules.

Taking hydrogen peroxide, how would you prepare oxygen in the laboratory ?

Take manganese dioxide in a round bottom flask and add hydrogen peroxide drop by drop to it, which acts a catalyst as shown in the figure. Collect oxygen by downward displacement of water.
1702941_1401398_ans_703b1842f60c4efe828280d1d2cd0876.png

1702941_1401398_ans_703b1842f60c4efe828280d1d2cd0876.png

Why is water not used as solvent synthesis of Grignard reagent?

Grignard reagent reacts with water faster than any other solvent which leads to the formation of alkanes. In this reaction, the nucleophile attack on one of hydrogen of water. Then magnesium in the solution will react with remaining OH ions which gives magnesium hydroxide.

Ether is used instead of water because Grignard reagent will not react with ether in the same way as it will react with water.

Why does hydrogen show dual nature ?

Hydrogen shows dual nature because it resembles the alkali metals of Group IA and the halogens of Group VIIA.

Is it possible for the atom of an element to have one electron, one proton or no neutron? If so, name the element.

Yes, it is true for the common, stable isotope of hydrogen (protium) which is represented as

$_{1}^{1}\textrm{H}$

An ice cube at $0^oC$ is placed in some liquid water at $0^oC$ , the ice cube sinks - why?
Discuss the three types of Covalent hydrides

1358283_1577838_ans_12e86d6842114639a5ee046cf70e8c66.jpg

Describe the different types of hydrides which are formed.

The harmful substances dissolved in water are ..........

Fill up is impurities.

Suggest reasons for and against the inclusion of hydrogen in the main groups of the periodic table.

Give the name and formula of the compounds as indicated in the following statement.
A compound of calcium and hydrogen which is used as a portable source of hydrogen for filling balloons.

Calcium hydride,

$CaH_2$

$CaH_2$ used as a portable source of hydrogen, for filling airships.

Why is the ionization enthalpy of hydrogen higher than that of sodium?

The size of hydrogen is smaller than that of sodium and therefore, the ionization enthalpy of

$H$ is higher

$(1312\,kJ\,mol^{-1})$ than that of

$Na$

$(496\,kJ\,mol^{-1})$ .

Why is water molecule polar?

Water molecule is polar due to the difference in electronegativity between

$O$ and

$H$ and it's

$\textbf {angular shape.}$

What is deionised water? Can distilled water be called as deionised water?

1567279_1726401_ans_261be4ed57024cefa09e2e90f483968d.jpg

Give three characteristics in which hydrogen resembles halogens.

1566852_1726410_ans_45024c53689e420fae9b3f3eb26564a0.JPG

Which is heavier, ice or water?

1567278_1726399_ans_dfdb9f50cb2d47319c074a411a12058f.jpg

Answer the following:
What is autoprotolysis of water?

1566856_1726394_ans_04d5e58a3a134e17835c1f8b7a354a87.JPG

Give the $pH$ of $D_2O$ and $H_2O$ at $298\ K$ .

In the case of

$D_2O$ the bonds are readily broken as compared to water. Hence, the ionic product of

$D_2O$ is less than that of water. Hence, pH of

$D_2O$ is more, i.e. 7.35 and of

$H_2O$ is 7.

Answer the following :
Name the chemical compound used in the preparation of $H_2O_2$ by auto- oxidation.

1567291_1726451_ans_57a9b5b682334f3ba03a1cc099d402cc.jpg

Give an example in which $H_2O$ acts as reducing agent.

$2F_2 +2H_2O \to O_2 +4HF$

In above reaction,

$H_2O$ acts as reducing agent.

Answer the following :
What type of hydrides are formed by the elements having low electronegativity?

1567283_1726427_ans_fe3183bcc0964b86b8de5d15e83b0ed7.jpg

Answer the following :
Why $D_2O$ has more density than $H_2O$ ?

1567289_1726441_ans_26ead4c21d7a4ac495902faa2b4c7bfa.jpg

Mention the condition in which the following statement is true.
Hydrogen can be prepared from water at ordinary temperature.

By electrolysis or by the action of some metal like sodium in the form of amalgam.

Give three characteristics in which hydrogen resembles alkali metals.

1566849_1726412_ans_5d426855e0cc4264852565f92963a7f5.jpg

Answer the following :
In which group of the periodic table, hydrogen is placed?

1567281_1726416_ans_fe086ead47074a438a7f56977bfed531.jpg

What happens when water reacts with the following compounds?

Antimony chloride $(SbCl_3)$ , bismuth chloride $(BiCl_3)$

$SbCl_3 + H_2O \rightleftharpoons Sb(OH)Cl_2 + HCl$

$Antimony(III)$ chloride reacts with water to produce

$antimony(III)$ hydroxide-dichloride and hydrogen chloride.

$BiCl_3+H_2O \rightleftharpoons BiOCl +2HCl$

When Bismuth chloride is reacted with an excess of water. Then it produces and forms a white precipitate

What happens when?
Water is added to aluminium nitride.

1676271_1728046_ans_da4b39bb20ea4cef97b59511079a7360.jpg

What happens when water reacts with the following compounds?
Red hot iron

Water reacts with metal under different conditions to liberate hydrogen gas.

$Na$ and

$K$ reacts with cold water.

$Mg$ and

$Fe$ reacts with steam.

On passing steam over red hot iron, it gives ferrosoferric oxide and

$H_{2}$ gas.

$3Fe(s)$ +

$4H_2O(l)$

$\rightarrow$

$Fe_3O_4(s)$ +

$4H_2(g)$

Answer the following:
What is plumbosolvency?

The dissolution of lead in water in presence of dissolved oxygen is known as plumbosolvency.

Answer the following question:
What happens when $F_{2}$ reacts with water?

It oxidises

$H_{2}O$ to

$O_{2}$ .

$2F_{2}(g) + 2H_{2}O(l)\rightarrow 4H^{+}(aq) + 4F^{-} (aq) + O_{2}(g)$ .

"Hydrogen occupies a unique position in Modern Periodic Table". Justify the statement.

Hydrogen occupies a unique position in Modern periodic Table; because of various reasons. From the context of atomic number, hydrogen occupies the correct position in Modern Periodic Table. However, hydrogen shows properties similar to elements of Group 1, IV and VII. Hydrogen shows the behavior of both electropositive and electronegative elements. Hence, it can be said that the position of hydrogen is still not decided in the Periodic Table. Elements having same number of valence electrons are placed in the same group. But it is treated to be more electropositive.

A sample of water under study was found to boil at $102^{\circ}C$ at normal pressure. Is the water pure? Will this water freeze at $0^{\circ}C$ ? Comment.

The boiling point of pure water is

$100^{\circ}C$ at

$1 atm$ . The freezing point of pure water is

$O^{\circ}C$ . The sample of water under study boils at

$102^{\circ}C$ at normal pressure. Hence, the sample is not pure water. Since the sample of water is not pure, it will not freeze at

$O^{\circ}C$ . It will freeze at a temperature below

$O^{\circ}C$ .

Melting point, enthalpy of vapourisation and viscosity data of $H_2O$ and $D_2O$ is given below:
On the basis of this data explain in which of these liquids intermolecular forces are stronger?

$D_2O$ has greater intermolecular force of attraction.

Complete the following reactions
(i) $O_{2}^{2-}+H_{2} O \rightarrow$

Peroxide ion reacts with water and forms hydrogen peroxide

$H_2O_2$

$O_{2}^{2-}+2 H_{2} O \rightarrow 2 O H^{-}+H_{2} O_{2}$

What is the fraction of the mass of water due to neutrons?

Mass of one neutron is

$1$ amu.
Mass of one water molecule is

$18$ amu.
Oxygen atom contains

$8$ neutrons and hydrogen atom contains no neutrons.
So the mass of neutrons in one water molecule is

$8$ amu.
The fraction of mass of water due to neutrons is

$\dfrac{8}{18}=\dfrac{4}{9}$

Write the balanced chemical equation for hydrogen peroxide catalyzed by manganese dioxide.

Hydrogen peroxide

$\xrightarrow{{\text{Manganese dioxide }}}$ Water + Oxygen

$2H_2O_2 \xrightarrow {MnO_2} \, 2H_2O + O_2$

Give a balanced chemical equation of the reaction for hydrogen gas preparation in the laboratory.

$Zn+2HCl \longrightarrow ZnCl_2 + H_2 \ (g)$

Complete the following reactions
(ii) $O_{2}^{-}+H_{2} O \rightarrow$

Superoxides reacts with water and forms

$H_2O_2 \ and \ O_2$

$2 O_{2}^{-}+2 H_{2} O \rightarrow 2 O H^{-}+H_{2} O_{2}+O_{2}$

Name:
A chemical called oxygenated water.

$H_2O_2$ (Hydrogen peroxide)

What is the effect on boiling point of water when
(a) pressure is increased
(b) impurity is added

(a) The boiling point of water increases with an increase in pressure.

(b) Any impurity present in water lowers its freezing point and raises its boiling point.

For example, salt is added to ice to lower its melting point. Such a mixture is called a freezing-mixture. The melting point of freezing mixture is about

$-15^{0}C$ .

Draw a neat and well-labelled diagram for the laboratory preparation of hydrogen.

1696086_1803407_ans_c91e76020e7342f19435de7510561482.png

Name the chemicals required to prepare hydrogen gas in the laboratory.

Granulated zinc and dil. hydrochloric acid.
1696078_1803404_ans_3ad75b57272145138d3ab57f560b9b41.jpg

Why is oxygen collected by downward displacement of water ?

Since the water is displaced downward by the gas collecting in the jar , the process is called downward of water, The reason are:

1. Oxygen is only slightly soluble in water. Therefore it can be collected over water without fear of excessive dilution.

2. Oxygen is slightly heavier than air, so it cannot collected over air.

Answer in brief: What is mineral water?

Mineral water is pure water fit for drinking. It is collected from natural source and contains air, minerals and salts free from suspended impurities, harmful bacteria and germs.

Name the gas produced when steam is passed over hot coke.

Water gas.
1695573_1804004_ans_0d1023c0c67a4c38a50bc1b1d25cb2a1.jpg

Why is hydrogen kept in the metal activity series?

Hydrogen is kept in the metal activity series because like metals it also loses its electron and for positive ion ie.

$H^{+}$ ion. It also helps to compare the reactivity of the metals.

Give any three important uses of water.

Water is indispensable for all living-organisms.

$70$ % of human body consists of water. Water sustains several life process in humans and animals. Water helps in controlling our body temperature. Water also generates electricity. Water keeps the environment and atmosphere mild when it is too hot.

Name two gases dissolved in natural water.

Hydrogen and oxygen gases are dissolved in water.

What is the smallest particle of water? Describe its structure.

The smallest particle of water is 'molecule'. The molecule of water is made up of two atoms of hydrogen

$(H_{2})$ and one atom of oxygen

$(O)$ . Both of these atoms combines to form a compound called water i.e,

$H_{2}+O\rightarrow H_{2}O$ .

Water has density and _ volume at $4^{0}C$ .

Statement with fill ups is:

Water has maximum density and minimum volume at

$4^{0}C$ .

Water molecules in loose chemical combination with other substances is called .........................

Fill up is water of crystallisation.

Why is hydrogen placed with alkali metals?

Hydrogen is placed with alkali metals as it has one electron in its valence shell similar to the alkali metals.

How are natural springs of water formed?

The percolated water gets collected beneath the earth on the non-porous rocks. This collected water forms the water-table. The ground water comes out of the surface at some places to form natural springs.

Why sea water does not freeze at $0^{0}C$ ?

There are impurities dissolved in sea water which decreases the freezing point. That is why sea water does not freeze at

$0^{0}C$ .

What nature does hydrogen show ?

Hydrogen resemble the alkali metals of Group

$1A$ and the halogens of Group

$VIIA$ hence it shows dual nature.

Compare hydrogen and halogens on the basis of:
Physical state

Both Halogens and Hydrogen are gases

Name a liquid that is an oxidizing as well as reducing agent.

Hydrogen peroxide

Why should a glass bottle completely filled with water never be kept in a freezer?

A glass bottle completely filled with water should not be kept in a freezer because the bottle can break and result in damage. We know that water expands after freezing and if a completely water filled glass bottle is placed in freezer, the water would freeze and would expand resulting in the bottle to break.

Explain the various properties of water.

$\cdot$ Water is a colourless, tasteless, and transparent liquid. It also has no smell.

$\cdot$ Boiling point of pure water is

$100^\circ C$ at 760 mm of Hg pressure. However, boiling point of water increases due to increase in pressure and presence of dissolved impurities.

$\cdot$ Pure water freezes at

$0^\circ C$ at 760 mm of Hg pressure. However, freezing point of water decreases due to increase in pressure and presence of dissolved impurities.

$\cdot$ The state of water changes on heating or cooling. On heating, the state of water changes from liquid state to gaseous state (vapour). Similarly, on cooling, the state of water changes from liquid state to solid state (ice).

$\cdot$ Water is neither acidic nor basic. It is neutral.

$\cdot$ Water is a bad conductor of heat and electricity.

$\cdot$ Water is an universal solvent as it can dissolve many substances in it.

Justify position of Hydrogen in the periodic table.

Hydrogen has atomic number

$1$ and it exist in the first group and

$1^{st}$ period of the periodic table. Hence it is the first element of the periodic table.

Compare hydrogen with alkali metals on the basis of:
Ion formation

Hydrogen and Alkali metals can from a cation by the loss of an electron.

They both are monovalent electropositive.

Apparatus for laboratory preparation of Hydrogen should be air right be air tight and away from a naked flame.

Apparatus for laboratory preparation of Hydrogen should be airtight and away from a naked flame because Hydrogen forms an explosive mixture with air to explode.

Compare hydrogen and halogens on the basis of:
Valency

Both Hydrogen and Halogens have the valency

$1$ .

How is pure $H_2$ obtained?

Pure

$H_2$ and

$O_2$ are obtained by electrolysis of acidified

$H_2O$ .

Why ethyl alcohol has lower boiling point than water?

Ethyl alcohol has a low boiling point. Because there are less extensive hydrogen bonding between ethanol molecules than between water molecules, thus less energy is needed to vaporise ethanol than water and water has a higher boiling point than ethanol.

What are the ways in which water molecules are bonded to an anhydrous salt to form a hydrate?

$\textbf {Co-ordinate bond }$ and

$\textbf { H-bond}$ are the ways in which water molecules are bonded to an anhydrous salt to form a hydrate.

Which type of bond is present in the water molecule?

$\textbf {Covalent bond and intermolecular Hydrogen bond.}$ is present in a water molecule.

Halima picks up a small stone from the ground and puts it in the water in a dish. Does the shape of the stone change ?

No, the shape of the stone will not change by putting it in a dish containing water because solids have definite shape. They do not change their shape and retain it, no matter whatever be the circumstances.

Write the molecular formula of water.

Molecular formula of water is

$H_2 O$

Why does water have a high boiling point and a high melting point as compared to $H_2S$ ?

Water molecules are associated with intermolecular H-bonding whereas

$H_2S$ is not. Thus water has a higher boiling point.

Riya pours some water from her bottle into another bottle. Does it change the shape of the water?

Yes, the shape of the water will change because liquids do not have a shape of their own. They take the shape of the container in which they are present.

Concentrated sulphuric acid cannot be used for drying $H_2$ . Why?

Conc.

$H_2SO_4$ on absorbing water from moist

$H_2$ produces so much heat that

$H_2$ catches fire.Hence it is not used for drying

$H_2$ .

Complete the reaction :
$Fe(s) + H_2O(g) \rightarrow \;?$

The complete reaction is :

$3 Fe(s) + 4H_2O (g) \rightarrow {Fe_3O_4(s) + 4H_2(g)}$

Why can dilute solution of hydrogen peroxide not be concentrated by heating?

$H_2O_2$ cannot be concentrated simply by heating because it decomposes much below its boiling point. Therefore, the concentration of

$H_2O_2$ is carried out in a number of stages.

In a reaction of $F_2$ and $H_2O$ , what is the role of water?

$2F_2+2H_2O \rightarrow 4HF + O_2$

Here water is acting as reducing agent.

Dilute solution of hydrogen peroxide cannot be heated strongly for its concentration. Explain.

Dilute solution of

$H_2O_2$ cannot be concentrated by heating because it decomposes into

$H_2$ and

$O_2$ on heating.

$H_2O_2 \xrightarrow{Heat} H_2 + O_2$

Which type of oxide is water?

$H_2O$ is an amphoteric oxide.Since water has the potential to act both as an acid and as a base, water is amphoteric.

Find the volume strength of the $2N$ $H_2O_2$ solution.

Volume strength

$= 5.6 \times Normality$
Volume strength

$= 5.6 \times 2$

$= 11.2$ volumes

Discuss the position of hydrogen in the periodic table is not justified.

Its position in the periodic table is not justified because it resembles both alkali metals and halogens.

Its electronic configuration is similar to alkali metals.
It is non-metal like halogens.
Its ionization energy is high like halogens.
It can lose electrons to form $H^+$ like alkali metals.

What is water gas and how it is obtained?

Water-gas is a mixture of

$CO$ and

$H_2$ . It is obtained by passing superheated steam over hot coke.

1735972_1826424_ans_a0fd1bf9dbf945f583487ce6f645fe37.jpg

How would you prepare dihydrogen from water by using a reducing agent?

The reaction is :

$2Na + 2H_2O \rightarrow 2NaOH + H_2$

What is the structure of $H_2O_2$ ? Draw a schematic diagram indicating the shape of the molecule clearly.

Hydrogen peroxide has an open-book structure. It has a non-planar structure. In the crystal, the dihedral angle

$111.5°$ reduces to

$90.2°$ on account of hydrogen bonding. There is a single bond between two oxygen atoms in hydrogen peroxide.
1736572_1826929_ans_b32362eaaae246209814353cae7dbd43.png

1736572_1826929_ans_b32362eaaae246209814353cae7dbd43.png

How would you prepare very pure $H_2$ in the laboratory?

It is obtained by electrolysis of acidified water.

$H^+$ ions are attracted to the cathode , gain electrons and form hydrogen gas.

$2H^+ + 2e^- \rightarrow {H_2(g)}$

$OH^-$ ions are attracted to the anode , lose electrons and form oxygen gas.

How would you prepare dihydrogen from a substance other than water?

The reacion is :

$Zn + 2HCl \rightarrow ZnCl_2 + H_2$

In what respects does hydrogen resemble alkali metals? How does it resemble halogen?

(i)

$\textbf {Resemble with alkali metals }$ :

It has one valence electron in s-orbital like alkali metals
It can lose one electron to form $H^+$ ion like alkali metals.
It is liberated at the cathode during electrolysis of compounds like $H_2O, HCl, etc.$
It shows a $+1$ oxidation state like alkali metals.
It is a strong reducing agent like other alkali metals.

(ii)

$\textbf {Resemblance with halogen}$ :

Hydrogen is non-metal like halogens.
Hydrogen forms diatomic molecules like halogens.
It has ionization energy high like halogens.
Its electronegativity is similar to halogens.
It can gain one electron to form $H^-$ ion.
When $NaH$ is electrolyzed, hydrogen is liberated at anode like halogens.

Describe the structure of the common form of ice.

In the normal hexagonal ice, each oxygen atom is tetrahedrally surrounded by four other oxygen atoms, there being a hydrogen atom in between each pair of oxygen. Each hydrogen is covalent bonded to one oxygen and linked to the other oxygen by a covalent bond. Such an arrangement leads to packing having large open spaces. The density of ice is therefore less than liquid water.
1736567_1826907_ans_f2bcb4626d794eadaad3c449a7ba30a3.png

1736567_1826907_ans_f2bcb4626d794eadaad3c449a7ba30a3.png

How is $H_2O_2$ manufactured?

Hydrogen peroxide is manufactured by electrolysis of

$50\%$

$H_2SO_4$ .
1744324_1826923_ans_ee28a52fd08c4cc5a56069cf6d94dbac.jpg

Sample of hydrogen peroxide solution is $1.5$ M. If it is to be labelled ‘X’ volume; what is the value of ‘X’.

$M = \dfrac{\text{Mass of solute}}{\text{Molecular mass} \times \text{Volume (in L)}}$

Mass of

$H_2O_2$ per liter

$= 1.5\times 34 = 51g$

$\underset{68g}{2H_2O_2} \longrightarrow 2H_2O + \underset{22.4L}{O_2}$

$68g$ of

$H_2O_2$ at STP gives

$22.4L$ of

$O_2$

$51g$ of

$H_2O_2$ gives at STP

$= \dfrac{22.4\times 51}{68}$

$=16.8L$ of

$H_2O_2$

Thus

$51g$ of

$H_2O_2$ will give

$16.8L$ of

$O_2$

Hence value of

$X$ is

$16.8L$ .

$\therefore$ The given sample of

$H_2O_2$ is

$16.8$ Litres.

Explain with examples :
Polymeric hybrids.

$\textbf {Polymeric hydrides}$ : These are formed by elements having electronegativity in the range of

$1.40 – 2.0$ . These usually exist in the polymeric form in which the monomer molecules are held together in two or three dimensions by hydrogen bridges. Some common examples are :

$(BeH_2)_n, (AlH_3)_n,(InH_3)_n, (GaH_3)_n, (SpH_4)_n$ These are amorphous solids which decompose above

$523$ K to evolve

$H_2$ gas.

Beryllium hydride exits in the polymeric form involving three-center-two electron bonds.

Explain with examples Complex hydrides.

$\textbf {Complex hydrides}$ : In these hydrides, the hydride ion

$(H^–)$ acts as the ligand and is attached to the central metal atom by coordinate bonds. These are formed both by transition elements and non-transition elements. Among the non-transition elements, the most important complex hydrides are formed by elements of the group

$13$ . These are sodium borohydride

$(NaBH_4)$ , lithium borohydride

$(LiBH_4)$ , and lithium aluminum hydride

$(LiAlH_4)$ . These are versatile reducing agents and are widely used for the reduction of organic compounds.

Describe the different methods by which the concentration of Hydrogen peroxide.

Concentration of hydrogen peroxide. Hydrogen peroxide obtained by any method is always in the form of a dilute solution. Great care is to be taken for concentrating its solution because it is unstable and decomposes on heating.

$2H_2O_2 \rightarrow 2H_2O + O_2$

The decomposition of

$H_2O_2$ is catalyzed by the ions of heavy metals present as impurities. The solution of

$H_2O_2$ is concentrated by the following methods.

(1)By careful evaporation on a water bath. A dilute solution of

$H_2O_2$ is taken in the evaporation dish and is heated at

$313-323\, K$ . Water evaporates slowly and hydrogen peroxide solution of about

$45-50\%$ strength is obtained.

(2) By dehydration in a vacuum desiccator. The dilute

$(50\%)$ solution of

$H_2O_2$ obtained is further concentrated by placing the same in a vacuum desiccator containing concentrated

$H_2SO_4$ as a dehydrating agent. Here water vapors are absorbed by concentrated sulphuric acid. This is shown in the diagram.

(3) By distillation under reduced pressure. The solution of hydrogen peroxide is further concentrated by subjecting it to distillation under reduced pressure. The solution is distilled at

$308-313\, K$ under a reduced pressure of

$15$ mm Hg. Water present in the solution distills over leaving behind about

$98-99\%$ concentrated solution of hydrogen peroxide.

(4) By crystallization. The last traces of water present in

$H_2O_2$ are removed by freezing it in a freezing mixture of solid

$CO_2$ and ether. The crystals of hydrogen peroxide separate out. These crystals are removed, dried, and then remelted to obtained

$100\%$ pure hydrogen peroxide.

(5) Storage of hydrogen peroxide. In order to check the decomposition of hydrogen peroxide, a small amount of acetanilide (i.e., negative catalyst) is added to it before storing the hydrogen peroxide. Hydrogen peroxide cannot be concentrated by distillation at ordinary pressure because it undergoes decomposition into water and oxygen as it is highly unstable liquid. It decomposes even on long-standing or on heating.
1744433_1827268_ans_9ae6060b4ddd419d95d6f4822c8606c1.png

1744433_1827268_ans_9ae6060b4ddd419d95d6f4822c8606c1.png

Calculate the volume of $10$ volume $H_2O_2$ required to neutralize $200$ mL of $2$ N $KMnO_4$ in acidic medium.

$22.4$ L of

$O_2$ at NTP is produced from

$H_2O_2 = 68g$

$10L$ of

$O_2$ at NTP is prodced from

$H_2O_2$

$=\dfrac{68}{22.4}\times10=30.357g$

Gram equivalents of

$H_2O_2 = \dfrac{30.357}{17} =1.79$

Normality of

$H_2O_2 = \frac{1.79}{1}=1.79\,N$

Applying normality equation,

$\underset{H_2O_2}{\underbrace{N_1V_1}}=\underset{KMnO_4}{\underbrace{N_2V_2}}$

$1. 79 \times V_1 = 2 \times 200$

$V_1=\dfrac{2 \times 200}{1.79}=223.5\,mL$

Calculate the normality of $20$ volume solution of $H_2O_2$ .

$20$ volume of

$H_2O_2$ solution means that

$1$ L of this solution will liberate

$20L$ of

$O_2$ at NTP

$\underset{68g}{2H_2O_2}\longrightarrow 2H_2O+\underset{22.4L\,at\,NTP}{O_2}$

$22.4L$ of

$O_2$ at NTP produced from

$H_2O_2 = 68g$

$20L$ of

$O_2$ at NTP is produced from

$H_2O_2 =\dfrac{68}{22.4} \times 20 = 60.71g$

Strength of

$H_2O_2 = 60.71\,g/L$

Gram equivalents of

$H_2O_2 = \dfrac{60.71}{17} = 3.57$

$Normality =\dfrac{3.57}{1}=3.57\,N$

$30$ mL of $H_2O_2$ solution after acidification required $30$ mL of $N/10$ $KMnO_4$ solution for complete oxidation. Calculate the percentage and volume strength of $H_2O_2$ solution.

To calculate the normality of

$H_2O_2$ solution, apply normality equation

$\underset{H_2O_2}{\underbrace{N_1V_1}}=\underset{KMnO_4}{\underbrace{N_2V_2}}$

For

$H_2O_2, V_1 = 40mL$ ,

$N_1 =?$ ;

For

$KMnO_4, V_2 = 30, N_2 =$

$N_1 \times 30 = \frac{N}{10} \times 30$

$N_1 = 0.1N$

Strength = Equivalent wt \times Normality

$= 17 \times 0.1 = 1.7\,g/L$

$\%$ of strength

$= \dfrac{1.7}{1000}× 100 = 0.17\%$

$H_2O_2$ decomposes as :

$\underset{68g}{2H_2O_2}\longrightarrow 2H_2O+\underset{22.4L\,at\,NTP}{O_2}$

$68$ g of

$H_2O_2$ agive

$O_2$ at NTP

$= 22.4L$

$1.7g$ of

$H_2O_2$ will give

$O_2$ at NTP

$= \dfrac{22.4}{60} \times 1.7 = 0.56L$

Write balanced equations for the following:
Hydrated Barium peroxide reacts with orthophosphoric acid.

$3BaO_2.8H_2O + 2H_3PO_4 \longrightarrow Ba_3(PO_4)_2 + 2H_2O_2 + 3H_2O$

Reaction of steam on hydrocarbon or coke at high temperature in the presence of catalyst yields a mixture of gases. Write a reaction to the above-mentioned process.

The reaction is :

$C_nH_{2n+2}+nH_2O \overset{1270K}{\underset{Ni}{\longrightarrow}}nCO+(2n+1)H_2$

$10$ ml of given $H_2O_2$ solution contains $0.91\,g$ of $H_2O_2$ . Express its strength in volumes.

$\underset{68g}{2H_2O_2}\longrightarrow 2H_2O+\underset{22.4L\,at\,NTP}{O_2}$

Amount of

$H_2O_2$ in

$1L=\dfrac{0.91 \times 1000}{10} = 91g$

$68g$ of

$H_2O_2$ give

$O_2$ at NTP

$= 22.4L$

$91g$ of will give

$O_2$ at NTP

$= \dfrac{22.4}{68} \times 91 = 30$

Since

$91\,g$ of is present in

$1L$ , Volume strength

$= 30$ volume

Find the volume strength of the $1.6N$ $H_2O_2$ solution.

$Strength = Normality \times Eq.\; wt.$

Eq. wt. of

$H_2O_2 =17$

∴ Strength of

$1.6\,NH_2O_2$ solution

$= 1.6 \times 17gL^{-1}$

Now

$68g$ of

$H_2O_2$ gives

$22400$ mL

$O_2$ at NTP/STP

∴

$1.6 \times 17g$ of

$H_2O_2$ will give

$=\dfrac{22400}{68} \times 1.6 \times 17 = 8960\,mL$ of

$O_2$ at STP

But

$1.6 \times 17g$ of

$H_2O_2$ are present in

$1000$ mL of

$H_2O_2$ solution.

Hence

$1000$ mL of

$H_2O_2$ solution gives

$8960$ mL of

$O_2$ at STP

$1$ mL of

$H_2O_2$ will give

$= 8.96$ mL of

$O_2$ at STP

Hence the volume strength of

$1.6\,N$

$H_2O_2$ solution is

$= 8.96$ volume.

How is hydrogen peroxide prepared industrially? Explain why it is stored in colored wax-lined glass or plastic bottles?

Industrially,

$H_2O_2$ is prepared by the auto-oxidation of

$2$ -ethylanthraquinol to

$2$ -ethyl anthraquinone.

$H_2O_2$ is stored in wax-lined glass or plastic bottles so that it does not decompose into

$H_2O$ and

$O_2$ . Because it is decomposed to

$H_2O$ and

$O_2$ when comes in contact with sunlight.

Calculate the volume strength of a $3\%$ solution of $H_2O_2$ .

To calculate the normality of

$H_2O_2$ solution, apply normality equation

$\underset{H_2O_2}{\underbrace{N_1V_1}}=\underset{KMnO_4}{\underbrace{N_2V_2}}$

For

$H_2O_2, V_1 = 40mL$ ,

$N_1 =?$ ;

For

$KMnO_4, V_2 = 30, N_2 =$

$N_1 \times 30 = \frac{N}{10} \times 30 N_1 =\frac{N}{10} \times \frac{30}{30} = N = 0.1N$

Strength = Equivalent wt \times Normality

$= 17 \times 0.1 = 1.7\,g/L$

$\%$ of strength

$= \dfrac{1.7}{1000}× 100 = 0.17\%$

$H_2O_2$ decomposes as :

$68$ g of

$H_2O_2$ gives

$O_2$ at NTP

$= 22.4L$

Hence

$1.7g$ of

$H_2O_2$ will give

$O_2$ at NTP

$= \dfrac{22.4}{60} \times 1.7 = 0.56L$

Calculate the amount of Hydrogen peroxide presents in $10$ ml of $25$ volume solution of $H_2O_2$ .

$\underset{68g}{2H_2O_2}\longrightarrow 2H_2O+\underset{22.4L\,at\,NTP}{O_2}$

$22.4L$ of

$O_2$ at NTP is produced from

$H_2O_2 = 68g$

$25L$ of

$O_2$ at NTP is produced from

$H_2O_2 = \dfrac{68}{22.4} ×\times 25 = 75.9g$

Strength of

$25$ volume

$H_2O_2 = 75.9\,g/L$

Amount of

$H_2O_2$ present in

$10mL =\frac{75.9}{1000} \times 10 = 0.759g$

Write the similarities of hydrogen with alkali metals.

There are following similarities of hydrogen with alkali metals
1. Electronic Configuration: The electronic configuration of hydrogen is

$1s^1$ which is similar to the outmost electronic configuration of alkali metals

$(ns^1)$ . Som it is placed with alkali metals in group

$1$
2. Electropopsitive Character: Hydrogen can from unipositive ion by losing one electron like alkali metals.
e.g.,

$H \to H^+ + e^-$

$Na\to Na^+ + e^-$
3. Oxidation State: Hydrogen exhibits oxidation state of

$+1$ ion the compounds of hydrogen which is similar to alkali metals.
4. Valency: Valency of hydrogen is

$1$ like alkali metals.
5. Reaction with Non-metals: Like alkali metals, hydrogen dorms binary compounds with non-metal,
6. Reducing nature: Hydrogen is a good reducing agent like alkali metals.

Ice floats on water. Give reason.

Along with the covalent bond & hydrogen bond, ice forms of water exist in the tetrahedral shape from the bent structure by leaving vacant space. Due to this vacant space density of ice becomes lower than that of water.

So, ice floats on water.

At what temperature, density of water is maximum.

$4^{o}C$ temperature, density of water is maximum.

How is the structure of hydrogen peroxide?

Hydrogen peroxide has a non-planar structure. It has an open book structure. The structure is shown as below
1739049_1829938_ans_dccbf893edbe44b8bb62791252f9ab67.png

1739049_1829938_ans_dccbf893edbe44b8bb62791252f9ab67.png

What is the reason of high boiling point of water?

The high boiling point of water is due to presence of inter-molecular hydrogen bonding in water. High energy is required to break the bond.

Write the similarities of hydrogen with halogens.

There are following similarities of hydrogen halogens:

(i) Electronic Configuration:

Electronic configuration of hydrogen

$=1s^1$

general electronic configuration of halogens

$=ns^2 np^5$

i.e. Hydrogen requires one electron to attain noble gas configuration. Similarly halogens also require one electrons to attain noble gas configuration.

(ii) Electronegative Nature: Hydrogen has tendency to attract electrons like halogens.

e.e.,

$H+e^- \to H^-$ (hydride ion)

$Cl + e^- \to Cl^-$ (chlorine ion)

(ii) Oxidation number: In addition to oxidation state of

$+1$ hydrogen shows oxidation state of

$-1$ like halogens in some of its compounds

e.g.,

$NaH$ (Oxidation state of

$H=-1$ )

$NaCl$ (Oxidation state of

$Cl=-1$ )

(iv) Valency : Valency of hydrogen is

$1$ like halogens.

(v) Reaction with metals: hydrogen combine with metals to form binary compounds similar to halogens.

e.g.,

$2Na+H_2 \to 2NaH$

$2Na+Cl_2 \to 2NaCl$

(vi) Atomicity Hydrogen exists in diatiomic form

$(H_2)$ like halogens (e.g.,

$Cl_2$ )

What is hydride? How many types of hydrides are there? Explain example.

Hydrides The binary compounds of dihydrogen with oredr elements except noble gases are called Hydrides

There are following types of hydrides:

1. Covalent of Molecular Hydride: Dehydrogen forms molecular hydrides with most of the

$p-$ block elements. They consist of discrete covalent molecules with are held together by weak Vander Waal's forces of attraction. They have low melting and boiling point. They are volatile in nature

e.g.,

$CH_4, NH_3, H_2O$ and

$HF$ .

These are of three types on the basis of relative number of electrons and bonds in their Lewis structure:

$\bullet$ Electron deficient hydride: Electrons of group

$13$ will electrons deficient hydride. They act as Lewis acids, e.g.

$B_2H_6$

$\bullet$ Electrons-precise hydride: All elements group

$14$ from electrons presise hydrides e.g,

$CH_4$

$\bullet$ Electrons hydride: Elements of group

$15-17$ from such compounds. They act as Lewis bases e.g

$NH_3$

2. Ionic or Saline hydride: These are stoichiometic compounds of hydrogen formed with most of the

$s-$ block elements. i.e., alkali and alkaline earth metals. These hydride are crystalline, non volatile and non-conducting solid state. They have high melting and boiling points.

e.e.,

$NaH, BeH_2, MgH_2$ etc.

3. Metallic or Interstitial hydrides: These hydrides are formed by the reaction of dihydrogen with

$d-$ block and

$f-$ block elements. Due to small size dihydrogen in these hydride, hydrogen occupies interstices in the metal lattice producing distribution without any charge in its type. So these are known as interstitial hydrides. These are non-stoichiometric being deficient in hydrogen.

e.g.,

$scH_2, LaH_2, T_2H_2, CrH_3$ etc.

What do you meant by molecular association in water. Explain the structure of water with diagram. Explain the normal structure of ice.

Molecular Association in Water: Molecular association, in Water is due to presence of inter, molecular hydrogen bonding

Structure of Water: A molecule of water consists of two hydrogen atoms joined to an oxygen atom by covalent bonds. The oxygen atom has six electrons in this outmost shell. The's and

$p$ orbital of the valence shell are

$sp^3$ hybridized to form four

$sp^3$ hybrid orbital oriented tetrahedrally around the oxygen atom. Two of the hybrid orbitals are singly occupied while the lone pairs of electrons occupy the other two. Each singly occupied

$sp^3$ orbital overlaps with the half filled

$1s$ orbital of

$H$ atom.

Hence oxygen is bonded to the two hydrogen atoms by two

$O-H$ covalent bonds and tow lone pairs of electrons are present on oxygen atom. Due to presence of lone pair of electrons on the

$O-$ atoms, the

$H-O-H$ bond angles is

$104.5^o$ , which is slightly less than the tetrahedral angle of

$109.28^o$ . The structure of water molecule is an angular or bent structure.

Structure of ice: Ice is crystalline from of water. It has highly ordered three dimensional structure with hydrogen bonds.

$X-$ ray studies show that each oxygen atom is surrounded tetrahedrally by four other oxygen atoms at a distance of

$276\ pm$ . One hydrogen atom lies in between each pair of oxygen atoms. So, each and eevry hydrogen atom is covalently bonded to an atom and linked to another oxygen atom by a hydrogen bond. This arrangement leads to a packing with large open spaces.

1739044_1829936_ans_321c7b6c32614bfc9d10ef229a04c417.png

It is justified to place hydrogen in a separate place in periodic table. Explain the statement.

The position of hydrogen in periodic table is a subject of discussion, due to similarities and dissimilarities of hydrogen with alkali metals and halogens. It is difficult to assign a specific position to hydrogen. On the basis of electronic configuration, it is suitable to place hydrogen on group

$1$ of periodic table. But this is not right, hence due to its abnormal behavior. It should be assigned a separate place in the periodic table. Keeping it walks other elements a drawback of periodic table.

Calculate molarity and normality of $20$ volumes of $H_2O_2$ . What is its mass percentage?

20 volume of

$H_2O_2$ solution means that 1L of this solution will liberate
20L of

$O_2$ at NTP

$\underset {68g}{2H_2O_2} \rightarrow 2H_2O+\underset {22.4L\;at\;NTP}{O_2}$

22.4L of

$O_2$ at NTP produced from

$H_2O_2$ = 68g

20L of

$O_2$ at NTP is produced from

$H_2O_2$ =

$\dfrac {68}{22.4}\times 20= 60.71g$

Strength of

$H_2O_2$ = 60.71g/L

Gram equivalents of

$H_2O_2$ =

$\dfrac {60.71}{17}= 3.57$

Normality=

$\dfrac {3.57}{1}=3.57N$

Molarity =

$\dfrac {N}{2} = 1.78$

Which is the substance that absorbed hydrogen and oxygen from sugar in the ratio as in water?

$Conc.\ H_2SO_4$ is the substance that absorbed hydrogen and oxygen from sugar in the ratio as in water

Explain the following reaction with respect to the hydrogen peroxide
Formation of peroxide

Formation of Peroxide: Dehydrated hydrogen peroxide (acidic in nature) reacts with base to form salts (peroxide)
1739058_1829941_ans_2ec9afaf0e574235a1c4f32b8a0913ad.png

1739058_1829941_ans_2ec9afaf0e574235a1c4f32b8a0913ad.png

Explain the laboratory method for preparation of dihydrogen.

Laboratory Method: In laboratory, dihydrogen is usually prepared the reaction of granulated Zinc with dilute sulphuric acid. In this method granulated Zinc is taken in Woulfs bottle and Sulphuric acid is mixed produced with help of a funnel. And the gas formed is collected in gas jar by water downward dislacement method.

$Zn +H_2SO_4\to ZnSO_4 +H_2 \uparrow$

List out the hydrogen compounds known to you

The hydrogen compounds are :

$H_2SO_4$
$HCl$
$HNO_3$
$H_2CO_3$
$H_2O$
$H_2O_2$
$NaOH$
$H_2PO_4$

The gas which is combustible and is formed through the electrolysis of water

$Hydrogen$ gas is combustible and is formed through the electrolysis of water.

What happens during the electrolysis of water? Complete its chemical equation given below
$2H_2O\xrightarrow{electricity}............ + .............$

$2H_2O \xrightarrow{electricity} 2H_2 + O_2$

Why is ice less dense than water and what kind of attractive forces must be overcome to melt ice?

The structure of ice is an open structure having a number of vacant spaces. Therefore, the density is less than water. When ice melts, the hydrogen bonds are broken and water molecules go in between the vacant spaces.

As a result, the structure of liquid water is less open than structure of ice. Thus, ice is less the dense than water.

Explain : (i) water has a maximum density at $277\, K$ . (ii) ice floats over water.

i)During ice phase of water, hydrogen bonds form a cage like structure. Hence, it occupies large volume, as temperature increases to

$277 \mathrm{k}$ ,hydrogen bonds are broken

hence volume decreases and density increases.

When temperature increases further molecular

repulsion increases and hence volume.

Therefore, water has it's maximum density at

$277 \mathrm{k}$

ii) Ice floats over water because it is about 9% less dense than liquid water

It is so because molecules form an ordered crystal through the hydrogen bonding. This ordered crystal spaces the various molecules father and father apart. Soon they are farther apart than when they were a liquid, which makes ice less dense than water.

When water is heated at its boiling point or melting point, its temperature does not change.
a. What is meant by boiling point and melting point?
b. What are the boiling and freezing points of water?
c. Why is there no change in temperature?

a. The temperature at which a liquid boils at normal atmospheric pressure is its boiling point. The temperature of a liquid at which it freezes to solid at normal atmospheric pressure is called its freezing point.

b. The boiling point and Freezing point of water are

$100^{0}C, 0^{0}C$ .

c. Once the water starts boiling, the temperature will not change because all the heat supplied is utilized for the change of state. So the temperature does not vary.

Is it correct to say that hydrogen can behave as a metal? State the conditions under which such behavior can be possible?

Yes,

$H_2$ can act as a metal under very very high pressures.

A definite quantity of water and coconut oil are heated in separate test tubes using the same amount of heat.
a. In which case does the temperature increase slowly?
b. What is the reason for this?
c. Write any one practical application of this property.

a. In case of Water, temperature increases slowly.
b. The reason for the slow heating of water is its high heat capacity.
c. 1. To regulates the heat of radiator in vehicles.
2. To regulate the heat of earth.

The volume of $O_2$ gas at S.T.P. obtained by the decomposition of 1 c.c. of $H_2O_2$ solutionis known as its volume strength.
If this is true enter 1, if false enter 0.

The statement is true. Answer:1

Volume of strength of

${ H }_{ 2 }{ O }_{ 2 }$ is the volume of

${ O }_{ 2 }$ gas at S.T.P obtained by the decomposition of

$1c.c$ of

${ H }_{ 2 }{ O }_{ 2 }$

Why do rivers and lakes not freeze easily ?

The density of water is approx. one gram per cubic centimeter. It is dependent on its temperature but the relation is not linear. When cooled from room temperature liquid water becomes dense but at

$4^0C$ pure water reaches its maximum density. As it is cooled it expands to become less dense. So the layer of ice floats on water as insulating layer. The warm layer settles at the bottom in winters.

Hydrogen may be prepared in the laboratory by the action of a metal on an acid. How would you modify your apparatus in to collect dry hydrogen ? Which drying agent would you employ for this purpose ?

Hydrogen can be made by reaction of any active metal like

$Mg$ or

$Zn$ with a strong acid sulfuric acid or hydrochloric acid. since hydrogen gas is almost insoluble in water it can be collected by displacement of water using an inverted bottle. The collected hydrogen will be saturated with water vapor and contaminated with small amount of air. the gas can be forced to move through calcium chloride pellets to remove water as drying agent.

What is meant by demineralised water and how can it be obtained?

Demineralized water is water free from salts and minerals. Ion exchange method is used for this process. The ions present in the water bind to the positively or negatively charged sites on a resin when water is passed through the column packed with resin.

Do you expect different products in solution when aluminium(III) chloride and potassium chloride treated separately with (i) normal water (ii) acidified the water, and (iii) alkaline water? Write equations wherever necessary.

$KCl$ is a salt of strong acid

$HCl$ and strong base

$KOH$ . Such salts are neutral in nature and do not undergo hydrolysis. In neutral water, acidic water and alkaline water,

$KCl$ dissociates as

$\displaystyle KCl \xrightarrow {Water} K^+ + Cl^-$

$\displaystyle AlCl_3$ is a salt of strong acid

$HCl$ and weak base

$\displaystyle Al(OH)_3$ .
In normal water, it is hydrolyzed.

$\displaystyle AlCl_3+3H_2O \rightarrow Al(OH)_3 + 3H^++3Cl^-$
In acidic water,

$\displaystyle H^+$ ions react with

$\displaystyle Al(OH)_3$ forming water and

$\displaystyle Al^{3+}$ ions. Hence it exists as

$\displaystyle Al^{3+}+Cl^-$

$\displaystyle AlCl_3 \xrightarrow [water]{acidified} Al^{+}+3Cl^-$
In alkaline water, the reaction is

$\displaystyle Al(OH)_3 + OH^- \rightarrow [Al(OH)_4]^-$

How can saline hydrides remove traces of water from organic compounds?

Ionic saline hydrides react with water to form metal hydroxide and hydrogen.

$\displaystyle MH + H_2O \rightarrow AOH + H_2 (A = Na,Ca....)$
On addition to organic solvents, saline hydrides react with water present in them. Hydrogen escapes and metallic hydroxides remains. The dry organic solvent is distilled out.

What do you expect the nature of hydrides is, if formed by elements of atomic numbers 15, 19, 23 and 44 with dihydrogen? Compare their behaviour towards water.

The elements with atomic numbers 15, 19, 23 and 44 are nitrogen, potassium, vanadium and ruthenium respectively.
Ammonia is a covalent compound. It contains lone pair of electrons on N. Hence, it is electron rich hydride.
Potassium hydride is ionic in nature due to high electropositive nature of potassium. It is crystalline and non volatile.
Vanadium and ruthenium hydries are nonstoichiometric metallic hydrides with hydrogen deficiency.
KH violently reacts with water.

$\displaystyle KH+ H_2O \rightarrow KOH + H_2$
Ammonia is a lewis base.

$\displaystyle NH_3 + H_2O \rightarrow OH^- + NH_4^+$
Vanadium and ruthenium hydrides do not react with water.
The increasing order of reactivity of hydrides towards water is

$\displaystyle V, Ru < H < NH_3< KH$ .

A hydride is a compound containing hydride ion, ${H}^{-}$ . Predict two elements whose hydrides would contain incomplete octets.

A hydride is a compound containing hydride ion.
Examples of hydrides of incomplete octets:

$LiH$ , and

$BeH_2$
here the valence shell of

$Li^{+}$ has 0 electron and

$H^{-}$ ( hydride ion) has 2 electron , hence octet is incomplete.
In the same way the

$Be^{2+}$ has 0 electrons in valence shell , and 2 hydrides ions have collectively 4 electrons in

$BeH_2$ , hence it is also incomplete.

Do you expect different products in solution when aluminium (III) chloride and potassium chloride treated separately with (i) normal water (ii) acidified water, and (iii) alkaline water? Write equations wherever necessary.

$KCl$ is a salt of strong acid

$HCl$ and strong base

$KOH$ . Such salts are neutral in nature and do not undergo hydrolysis. In neutral water, acidic water and alkaline water,

$KCl$ dissociates as:

$\displaystyle KCl \xrightarrow {Water} K^+ + Cl^-$

$\displaystyle AlCl_3$ is a salt of strong acid

$HCl$ and weak base

$\displaystyle Al(OH)_3$ .

In normal water, it is hydrolyzed.

$\displaystyle AlCl_3+3H_2O \rightarrow Al(OH)_3 + 3H^++3Cl^-$

In acidic water,

$\displaystyle H^+$ ions react with

$\displaystyle Al(OH)_3$ (obtained from the hydrolysis of

$AlCl_3$ ) forming water and

$\displaystyle Al^{3+}$ ions. Hence it exists as

$\displaystyle Al^{3+}+Cl^-$ .

$\displaystyle AlCl_3 \xrightarrow [water]{acidified} Al^{3+}+3Cl^-$

In alkaline water, the

$Al(OH)_3$ obtained from hydrolysis of

$AlCl_3$ reacts with hydroxide ions of alkali. The reaction is:

$\displaystyle Al(OH)_3 + OH^- \rightarrow [Al(OH)_4]^-$

The drain cleaner, Drainex contains small bits of aluminum which react with caustic soda to produce dihydrogen. What volume of dihydrogen at $20^o C$ and one bar will be released when 0.15 g of aluminum reacts?

The reaction can be written as:-

$2Al_{(s)}+2NaOH_{(aq)}+2H_2O_{(l)}\longrightarrow {2NaAlO_2}_{(aq)}+{3H_2}_{(g)}$

Here,

$2$ moles of

$Al$ gives

$3$ moles of

$H_2$ gas.

Moles of aluminium=

$\cfrac {0.15g}{27}=5.56\times 10^{-3}$ moles

$\therefore$ Moles of

$H_2$ produced=

$\cfrac {3}{2}\times 5.56\times 10^{-3}$

$8.33\times 10^{-3}$ moles

$\therefore$ Volume of

$H_2$ =

$\cfrac {nRT}{P}$

$\cfrac {8.33\times 10^{-3}\times 0.0831\times 293}{1}$

$0.203$ litres

$\therefore$ Volume of dihydrogen released is

$0.203$ litres

The drain cleaner, Drainex contains small bits of aluminium which react with caustic soda to produce dihydrogen. What volume of dihydrogen at $20C$ and one bar will be released when $0.15g$ of aluminium reacts?

Aluminum reacts with caustic soda in accordance with the reaction

The reaction of aluminum with caustic soda can be represented as:

2 $Al$ + 2 $NaOH$ + 2 $H_2O$ $\rightarrow$ 2 $NaAlO_2$ + 3 $H_2$

$2\times 27 g$ $3\times 22400 mL$

Therefore volume of hydrogen at STP released when 0.15g of Al reacts

$=0.15 \times 3 \times \dfrac{22.4}{54} = 187ml$

Now $P_1 = 1 bar$ ,

$P_2 = 1 bar$

$T_1=273 K$

$T_2=20 + 273 = 293 K$

$V_1=187 ml$

$V_2=?$

When pressure is held constant, then

$V_2=\dfrac{P_1 \times V_1 \times T_2}{P_2\times T_1}$

$V_2 =\dfrac{1 \times 187 \times 293}{0.987 \times 273}$

$= 201 ml$

Therefore, 201 mL of dihydrogen will be released.

The drain cleaner, Drainex contains small bits of aluminium which react with caustic soda to produce dihydrogen. What volume of dihydrogen at $20^{\circ}C$ and one bar will be released when $0.15$ g of aluminium reacts?

Solution:-

The balanced reaction is-

$2Al + 2NaOH + 2{H}_{2}O \longrightarrow 2NaAl{O}_{2} + 3{H}_{2}$

At STP:

2 moles of aluminium reacts to form 3 moles of dihydrogen, i.e., 54g of aluminium reacts to form 67200 mL

$\left( 22400 \times 3 \right)$ of dihydrogen.

$\therefore$ 0.15 g of aluminium gives 186.67 mL

$\left( \cfrac{67200}{54} \times 0.15 \right)$ of dihydrogen

At STP:

${P}_{1} = 1atm$

${V}_{1} = 186.67 mL$

${T}_{1} = 273 K$

Let the volume of hydrogen be

${V}_{2} = V$ at:

${P}_{2} = 1 bar = 0.0987 atm$

${T}_{2} = 20℃ = 293 K$

As we know that,

$\cfrac{{P}_{1} {V}_{1}}{{T}_{1}} = \cfrac{{P}_{2} {V}_{2}}{{T}_{2}}$

$\therefore \; \cfrac{ 1 \times 186.67}{273} = \cfrac{0.987 \times V}{293}$

$\Rightarrow \; V = \cfrac{186.67 \times 293}{273 \times 0.0987} = 202.98 \approx 203 mL$

Observe the following activity and and answer the questions
(a) Do you observe anything happening around the zinc granules ?
(b) Is there any change in its temperature ?
(c) Why is glass tube not dipped in dil $H_2SO_4$ ?
(d) How is $H_2$ gas collected by downward displacement or upward displacement of water ?
(e) Is $H_2$ gas soluble or insoluble in water ?
(f) Is $H_2$ gas heavier or lighter than air ?

$Zn+{ H }_{ 2 }{ SO }_{ 4 }\longrightarrow { ZnSO }_{ 4 }+{ H }_{ 2 }\uparrow$

$\left( \ast \right)$ We can observe bubbles of

${ H }_{ 2 }$ gas being formed around zinc granules.

$\left( \ast \right)$ This is an exothermic reaction, i.e. it involves release heat and the flask become hot and temperature of the system increases.

$\left( \ast \right)$ The glass tube is not dipped in the solution so as to collect enough,

${ H }_{ 2 }$ gas. It is was dipped in

${ H }_{ 2 }{ SO }_{ 4 }$ solution would enter the tube presenting

${ H }_{ 2 }$ gas to enter the tube.

$\left( \ast \right)$

${ H }_{ 2 }$ gas is collected by downward displacement of water.

$\left( \ast \right)$

${ H }_{ 2 }$ gas is insoluble in water.

$\left( \ast \right)$

${ H }_{ 2 }$ gas is lighter than air.

When water is heated at a temperature x by a process called P. And when steam gets reconverted at the same temperature into water and the process is called as Q.
(a) What is the temperature x in kelvin?
(b) what is the process P & Q known as?
(c) Name the energy released and absorbed during process P & Q respectively?

water is heated at

$373k$ by boiling and converted to steam.

Steam is reconverted to water by condensation.

Energy released and absorbed during

$P$ and

$Q$ is called latent heat of vapourization.

What are electrons deficient and electron rich compounds of hydrogen? Give examples.

The hydrides which have tendency to accept electrons in order to make octet. Group 13 hydrides(compounds of hydrogen), mainly hydrides of Aluminium and Barium are called electron deficient hydrides. For example:

$BH_{3}$

Electron rich hydride is the type of hydride in which the number of electrons present are more than the number of electron required to make the octet. The hydrides of group 15 are electron rich. For example:

$NH_{3}$

Explain why on addition of $1$ mol of NaCl to $1$ litre of water, the boiling point of water increases, while addition of $1$ mol of methyl alcohol to one litre of water decreases its boiling point.

Methyl alcohol is more volatile than water. But

NaCl is non-volatile solute. On addition of NaCl

in water , vapour pressure is lowered and as a

result boiling point of water increased. But on

addition of methyl alcohol ,vapour pressure is

more than that of water. Hence boiling point

decreases.

What is negative catalyst? Which is the negative catalyst in the decomposition of $H_2O_2$ ?

A negative catalyst is a substance which decreases the rate of a chemical reaction.

Phosphoric acid serves as a negative catalyst in the decomposition of

$H_{2}O_{2}$

Give examples of ionic hydride, molecular hydrides, interstitial hydride, electron precise hydride.

Ionic hydride: Sodium Hydride(NaH) , Lithium Hydride(LiH) , Potassium Hydride(KH) etc.

Molecular hydride: Water(

$H_{2}O$ ) , Hydrogen Flouride(HF),

$PH_{3}$

Interstitial hydride:

$ZnH_{2}$ ,

$ScH_{2}$ ,

$YH_{2}$ ,

$LaH_{3}$ etc.

Electron precise hydride:

$NH_{3}$ ,

$PH_{3}$ ,

$H_{2}S$ etc.

Comment on the reactions of dihydrogen with
$(i)$ Chlorine
$(ii)$ sodium, and
$(iii)$ copper $(ii)$ oxide

1338198_1318050_ans_d4b93131432f4b74ac7ce1adee3bca4e.jpg

What do you understand by the term 'auto-protolysis' of water? What is its significance?

1874259_1352947_ans_403e776c8af44cf4b0c37a2b01ec1cf7.jpeg

Compare the structure of $H_{2}O$ and $H_{2}O_{2}$ .

$H_2O_2$ has a half open book structure where as the

$H_2O$ has bent V-shape as given in the structures below
1218828_1369263_ans_cbcf56e7892b4db8b2274ee81141d3ea.png

What types of elements form interstitial hydrides?

d- and f-block elements form interstitial hydrides.

Why Nitric acid is not used for the preparation of hydrogen ?

Nitric acid not used in the preparation of hydrogen because Nitric acid is a powerful oxidizing agent, and the oxygen formed due to its decomposition oxidizes hydrogen to give water thus defeating the purpose of the reaction

$3Zn+8HNO_3 \rightarrow 3Zn(NO_3)_2+4H_2O+2NO$

Distinguish clearly between salt-like and covalent hydrides.

Salt-like hydrides are also called ionic hydrides. They are formed by group $1$ and $2$ elements with $H_2$ . They are basic in nature. They dissolve in water forming alkali and give $H_2$ gas, .e.g., $NaH, CaH_2, KH,$ etc.

Covalent hydrides are formed between less electropositive or electronegative elements. Ex: $B_2H_6, AlH_3, BeH_2,$ They are insoluble in water.

Why does elemental hydrogen react with other substances only slowly at room temperature?

Elemental hydrogen reacts with other substances slowly at room temperature because it has high bond dissociation energy

$(436\,kJ\,mol^{-1})$

Draw the gas phase and solid phase structure of $H_2O_2$ .

1881164_1725298_ans_d3784bd2e6b8473b98fa3081ffe9bcf7.jpeg

What are the metallic/interstitial hydrides? How do they differ from molecular hydrides?

2038847_1725130_ans_79e0cf9db7a54ca781c04efd411ed2c4.jpg

Name the classes of hydrides to which $H_2O,$ $B_2H_6$ and $NaH$ belong.

1982623_1725106_ans_722e1d21a56b42b9bac7173e2da4e05d.jpg

If same mass of liquid water and a piece of ice is taken, then why is the density of ice less than that of liquid water?

1982630_1725115_ans_1fc598cf3484410e93adcb366821eae8.jpg

Melting point, enthalpy of vaporization and viscosity data of $H_2O$ and $D_2O$ is given below:
Properties $H_2O$ $D_2O$
Melting point K $373.0$ $374.4$
Enthalpy of vaporization at
$(373K)/kj\,mol^{-1}$ $40.66$ $41.61$
Viscosity/centipoise $0.8903$ $1.107$
On the basis of these data, explain in which of these liquids intermolecular forces are stronger?

2038858_1725309_ans_336a022650034203b832547b83d6ff0f.jpg

Give reasons: (a) Lakes freeze from top towards bottom.
(b) Ice floats on water.

1980829_1725272_ans_eac3ead1f16347a9bc254c2f4983ad68.jpg

Molecular hydrides are classified as electron deficient, electron precise and electron-rich compounds. Explain each type with two examples

1980834_1725280_ans_2a82e396a009436c9ceb5440f7abf1db.jpg

Phosphoric acid is preferred over sulphuric acid in preparing hydrogen peroxide from peroxides. Why?

2038861_1725361_ans_c0b2aa8f71694a08aedec2237c43657c.jpg

Give reasons why hydrogen resembles alkali metals?

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1986849_1725327_ans_e89fdb031d45417bb48eee1fdf4f3c9e.jpg

Why does water show higher boiling point as compared to hydrogen sulphide? Give reasons for your answer.

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1981749_1725348_ans_542ccd2c1b3b44348f3035a94d232857.jpg

Give a method for the manufacture of hydrogen peroxide and explain the reactions involved therein.

1898301_1725406_ans_9fa66104196547998f1d6c914fd400e3.jpeg

An ionic hydride of an alkali metal has significant covalent character and is almost unreactive towards oxygen and chlorine. This is used in the synthesis of other useful hydrides. Write the formula of this hydride. Write its reaction with $Al_2Cl_6$

Since the ionic hydride of alkali metal has a significant covalent character, therefore, it is

$LiH$ . Since

$LiH$ is very stable, therefore, it is almost unreactive towards

$O_2$ and

$Cl_2$ . It reacts with

$Al_2Cl_6$ form lithium aluminum hydride.

$8LiH + Al_2Cl_6 \rightarrow 2LiAlH_4+6LiCl$

A colourless liquid 'A' contains H and O elements only. It decomposes slowly on exposure to light. It is stabilized by mixing urea to store in the presence of light.
Suggest a possible structure of A.

The liquid A is hydrogen peroxide

$(H_2O_2)$
1735805_1725413_ans_989b0caa0cb349b0a1e4a94e7d5d1b24.png

How will you account for $104.5^0$ bond angle in water?

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1981750_1725365_ans_8c0b8f606cc0484a97d4489c71748769.jpg

Which one is a covalent hydride?
$BeH_2, NaH, CaH_2$

1733584_1725630_ans_d631f7279d0a4ad5966cce7f9ac6e58e.jpg

Write short notes on:
Strength of hydrogen peroxide

1562027_1726525_ans_917c337708a34146937e7c9395e266cb.jpg

Give reason
Presence of water is avoided in the preparation of $H_2O_2$ from $Na_2O_2$ .

Water reacts with

$Na_2O_2$ to produce

$NaOH$ which increases the decomposition of

$H_2O_2$ .

What is perhydrol? Give its composition and use

$30\% H_2O_2$ is called perhydrol which is used as an antiseptic and germicide for washing wounds, teeth and ears.

What happens when water is added to calcium phosphide?

1669367_1728506_ans_8c2628082b7d435f842c5470b0fbdbca.jpg

What happens when?

Excess of water is added to a concentrated solution of antimony chloride.

When the concentrated solution of antimony chloride reacts with an excess of water, it forms basic, white insoluble salt SbOCl.

The reaction is as given below:

$SbCl_{3}(aq) + H_{2}O(l) \rightarrow SbOCl (s) + 2HCl (aq)$

Why does the hardness of water render it unfit for washing purposes?

If hard water is used, calcium and magnesium ions of the water combine with the negative ions of the soap to form a slimy precipitate of insoluble calcium and magnesium usually called soap curd (scum).

Formation of soap curd will go on as long as calcium and magnesium ions are present. Till then, no soap lather will be formed and the cleaning of clothes or bodies will not be possible. Moreover, these precipitates are difficult to wash from fabrics and sometimes form rusty spots if iron salts are present in water.

Phosphoric acid is preferred over sulphuric acid in preparing hydrogen peroxide from peroxides. Why?

$H_2SO_4$ can activate the decomposition of

$H_2O_2$ . That's why some weaker acids such as

$H_3PO_4$ is preferred over

$H_2SO_4$

Compare hydrogen with alkali metals on the basis of:
Reducing -power

Both Hydrogen atoms and alkali metals are reducing agent.

(i) Draw the gas phase and solid phase structure of $H_2O_2$ .
(ii) $H_2O_2$ is a better oxidising agent than water. Explain.

(ii) In

$H_2O_2$ oxygen is in -1 oxidation state which has tendency to become -2 that is why it is better oxidising agent than water.

1660587_1795145_ans_bf179912d96a4d6cad55dbde28328288.png

Name the classes of hydrides to which $H_2O, B_2H_6$ and $NaH$ belong.

$NaH$ belongs to Saline hydrides and

$B_2H_6$ and

$H_2O$ belong to molecular hydrides

For laboratory preparation of hydrogen, give the following fully labelled diagram

1696010_1809747_ans_dbe5ec1685c34ae5aff8c6c4d964425b.png

Compare hydrogen and halogens on the basis of:
Reduction with oxygen

Hydrogen reacts with oxygen to form neutral oxides. Halogens reacts with oxygen to form acidic oxides.

For laboratory preparation of hydrogen, give the following materials used

Granulated zinc, dilute

$HCl$ or dil.

$H_2SO_4$

For laboratory preparation of hydrogen, give the following chemical equation

$Zn+HCl \rightarrow ZnCl_2+H_2$

For laboratory preparation of hydrogen, give the following method of collection

It is collected by the downward displacement of water.

In what respect does hydrogen differ from
Alkali metals

Oxides of alkali metals are basic, whereas oxides is a natural oxide.

Compare hydrogen with alkali metals on the basis of:
Reduction with oxygen

Both alkali metal and Hydrogen burns in air to form oxides.

Compare hydrogen with alkali metals on the basis of:
Oxygen formation

Hydrogen and Alkali metals can form oxides on reaction with Oxygen.

In what respect does hydrogen differ from
Halogens

Hydrogen atoms has only one shell, but halogens have two or more shells.

Compare hydrogen and halogens on the basis of:
Ion formation

Both of them from anions as they are short of

$1$ electrons to take stable confirmation.

They both are monovalent electronegative

Which gas is evolved when $Mg_3N_2$ (Magnesium nitride) is treated with $H_2O$ ? Give chemical reactions.

Reaction is :

$Mg_3N_2 +6H_2O \rightarrow 3Mg(OH)_2 +2NH_3$

$NH_3$ gas is evolved.

Anhydrous $BaO_2$ is not used for preparing $H_2O_2$ . Why?

$BaSO_4$ is formed during the reaction of

$BaO_2$ with

$H_2SO_4$ ; it forms a protective layer around unreacted

$BaO_2$ and the reaction stops after some time.

What is the strength of $10$ volume $$H_2O_2$$.

1990156_1826320_ans_5d90397f5a024587817e04f199db9fb5.jpg

Give an example of each of an ionic hydride and a covalent hydride.

Ionic:

$NaH$ or

$CaH_2$

Covalent:

$H_2O,B_2H_6,CH_4$ etc.

When sodium hydride is electrolyzed, hydrogen is liberated at which electrode? Give an equation.

$NaH\xrightarrow {Electrolysis}{Na^+ + H^-}$

At anode;

$2H^– – 2e^– \rightarrow H_2(g)$

Give two examples of interstitial hydrides.

$CuH$ ,

$FeH$ are examples of interstitial hydrides.

What is the strength of $20$ volume $H_2O_2$ .

1990159_1826321_ans_f7cfaa279a274f50b5ecdb3bccebc802.jpg

Write the properties of Water.

Water is a fluid which is used as a universal solvent in many of the solutions.

Reaction of steam on hydrocarbon or coke at high temperature in the presence of catalyst yields a mixture of gases. What is a specific name given to the mixture of gases?

Specific name :

$\textbf {Synthetic gas or syngas or water gas.}$

Reaction of steam on hydrocarbon or coke at high temperature in the presence of catalyst yields a mixture of gases. Name the gases produced.

$C_nH_{2n+2}+nH_2O \overset{1270K}{\underset{Ni}{\longrightarrow}}nCO+(2n+1)H_2$

The gases produced are:

Carbon monoxide(

$CO$ ) and dihydrogen(

$H_2$ )

Why do lakes freeze from the top towards the bottom ?

The upper surface of the lake is in contact with the cold environment and starts to freeze. The density of ice is less than that of liquid water. Therefore, ice floats on the surface. Thus, the ice layer at lower temperature floats over the water below it. Due to this, the freezing of water into ice occurs continuously from the top towards the bottom.

What do you understand by metallic hydrides?

$\textbf {Metallic hydrides}$ are hydrides formed by transition metals with hydrogen. They are non-stoichiometric compounds, i.e., they do not have a fixed composition.

Ionisation energy of hydrogen is much higher than those of alkali metals. In case of the former combines with the latter, which type of compound will be formed? Explain when $H_2$ reacts with C at high temperature, what type of hydride will be formed. Give the chemical equations.

$2Na + H_2 \rightarrow {2NaH}$
Ionic hydride will be formed,

$C + 2H_2 \xrightarrow {Heat} {CH_4}$
Methane gas is a covalent hydride

Fill in blanks:
H+ ion in water exists as ……… ion called …………….

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1990808_1826975_ans_5df75538e40e444788bb5522439e038a.jpg

Reaction of steam on hydrocarbon or coke at high temperature in the presence of catalyst yields a mixture of gases. Write the reaction when the mixture of gases is reacted with steam in the presence of iron chromate as a catalyst.

$CO(g)+H_2O(l)\overset{673K}{\underset{FeCrO_4}{\longrightarrow}}CO_2(g)+H_2(g)$

The Water-gas shift reaction is the special name of this reaction.

The process $\dfrac{1}{2}H_2(g) + e^– → H^– (g)$ is endothermic $(\Delta H =+151kJmol^{-1})$ , yet salt like hydrides are known. How do you account for this?

It is true that formation of hydride (

$H^–$ ) ion is an endothermic process, yet alkali and alkaline earth metals from salt-like hydrides. This is due to the reason that high lattice energy released (energy released during the formation of solid metal hydrides from their corresponding ions, i.e.,

$M^+$ and

$H^–$ ) more than compensates the energy needed for the formation of

$H^–$ ions from

$H_2$ gas.

Write two methods to reduce the surface tension of water.

Two methods to reduce the surface tension of water are:

1. Add soap to water.
2. Boil the water.

The Boiling point of $H_2O$ is higher than that of $H_2S$ . Explain.

Due to extensive intermolecular H-bonding in

$H_2O$ , the b.p. of

$H_2O$ is much higher than that of

$H_2S$ .

Soap decrease the surface tension of water.
a. What is surface tension?
b. How does the decrease in surface tension benefit washing of clothes?

a. The unbalanced attractive force on the surface of a liquid causes the liquid surface behaves like a stretched membrane. This is surface tension

b. When we add soap to water it reduces the surface tension of water and water can enter into the fine threads of the fabric.

Sodium fir in the laboratory should Do not be extinguished by Pouring Water .Why ?

Sodium reacts violently with water producing

$H_2$ gas which also catches fire. As a result, the fire spreads rather than being extinguished. Therefore,

$H_2O$ should not be used for extinguishing sodium fire. Instead pyrene

$(CCI_4)$ should be used.

Explain why beryllium forms a covalent hydride while calcium forms an ionic hydride.

Because of higher electronegativity

$(E.N. = 1.5)$ , Be forms covalent hydride while due to lower electronegativity

$(E.N. = 1.0)$ Ca forms ionic hydride.

100 ml each of coconut oil and water are taken in two beakers and kept in the freezer.
a. What difference can be observed in their volumes during freezing?
b. What do you infer from the observation?
c. When water is frozen in glass bottles, it is advised not to fill the bottles completely. Explain the reason.

a. The volume of the beaker containing water is greater.
b. Due to the anomalous expansion of water.
c. The volume of water in the bottle filled with water is increased and the bottle is broken.

In the following reactions assign for underlined atom for product of complete hydrolysis at R.T.
A. If product is oxy acid with —ic suffix.
B. If product is oxy acid with —ous suffix.
C. If product are two oxy acids one with —ic suffix and another one with —ous suffix.
D. If product is not oxy acid, neither with —ic suffix nor with —ous suffix.
$H_4\underline B_2O_6+H_2O \longrightarrow H_3BO_3+H_2O_2$

2033775_1862076_ans_f223ca143709488d855287c8aaa9f047.png

Can marine species live in distilled water?

No, marine species live in distilled water because distilled

$H_2O$ does not contain dissolved

$O_2$ .

Discuss briefly the characteristics of salt like hydrides.

(i) Ionic hydride

Ionic hydrides are formed by Hydrogen with s-block elements. Eg

$LiH$ ,

$NaH$ ,

$CsH$ ,

$MgH_2$ ,

$CaH_2$ (Except

$BeH_2$ which is a covalent hydride).

These metal hydrides have high melting point and conductance in molten form.

These hydrides in

$H_2 O$ release

$H_2$ .

These all are strong reducing agent.

(ii) Covalent hydrides

Covalent hydrides are formed by hydrogen with p-block elements.

Eg-

$(BH_3)_n , (AlH_3)_n , (InH_3)_n ,$ - 13 group hydride

$CH_4 , SiH_4 , GeH_4 , SnH_4$ - 14 group hydride

$NH_3, PH_3 , AsH_3 , BiH_3$ - 15 group hydride

Group 13 hydrides are called Lewis Acid.

Group 16 elements are called Lewis base.

Explain why electrolysis of ordinary water occurs faster than heavy water.

Due to lower bond dissociation energy of protium bonds in

$H—O—H$ than deuterium bonds in

$D—O—D$ , electrolysis of

$H_2O$ occurs much faster than that of

$D_2O$ .

How is dihydrogen obtained from
(i) water (ii) dilute acids (iii) alkalies?

(i) Water

Dihydrogen may be obtained from water by reduction either active metals or by electricity.

(a) By action of water on active metals:

(I) Cold Water - Very active metals i.e. alkali and certain alkaline earth metals i.e.

$Na$ ,

$K$ ,

$Ca$ react with water at room temperature evolving dihydrogen.

$2Na+2H_2O \longrightarrow2NaOH+H_2$

$2K+H_2O\longrightarrow 2KOH+H_2$

$Ca+2H_2O\longrightarrow Ca(OH)_2+H_2$

(II) Boiling water - Less active metals like

$Zn$ ,

$Mg$ ,

$Al$ decompose boiling water liberating dihydrogen.

$Zn+H_2O \longrightarrow ZnO +H_2$

$Mg + H_2O \longrightarrow MgO+H_2$

$2Al+3H_2O \longrightarrow Al_2O_3 +3H_2$

(III) Steam - Still less reactive metals like

$Fe$ ,

$Sn$ ,

$Ni$ decompose steam at high temperature evolving digydrogen.

$3Fe+4H_2O\longrightarrow Fe_3O_4 +H_2$

(b) By electrolysis of water:

Dihydrogen of high purity is usually obtained by electrolysis of water in presence of small amount of acid/base. During electrolysis, dihydrogen is collected at cathode an dioxygen is collected at anode.

$2H_2O \longrightarrow 2H_2 +O_2$

(ii) Dilute acids

Metals which are more electropositive than hydrogen such as

$Zn$ ,

$Mg$ ,

$Fe$ react with dilute mineral acids to liberate dihydrogen gas.

$Zn + H_2SO_4 \longrightarrow ZnSo_4 + H_2$

$Fe+2HCl \longrightarrow FeCl_2 +H_2$

(iii) Alkalies

Metals like

$Be$ ,

$Zn$ ,

$Sn$ react with boiling alkali solution liberating dihydrogen

$Be+2NaOH \longrightarrow Na_2BeO_2 +H_2$

$Zn +2NaOH \longrightarrow Na_2 ZnO_2 +H_2$

$Sn+2NaOH +H_2O \longrightarrow Na_2SnO_3+ H_2$

$2Al +2NaOH+2H_2O \longrightarrow 2NaAlO_2 +3H_2$

In the reaction of $F_2$ with $H_2O$ , water acts as a ................ .

$\text {In the reaction of } F_{2} \text { and } \mathrm{H}_{2} \mathrm{O} \text {, water acts as a } \\$

$\text {Reducing agent because in reaction } F_{2} \text { is converted into } \\$

$\text {Hydrogen fluoride }\left(\mathrm{H}^{+} \mathrm{F}^{-}\right) \text {and liberates oxygen. }$

$2 F_{2}(g)+2 H_{2} O_{(l)} \longrightarrow 4 H_{(a q)}^{+}+4 F^-_{(a q)}+O_{2}(g)$

The electrolysis of molten sodium hydride liberates ............... gas at the anode.

$\text {Preparation of Hydrogen :- } \\$

$\text {The electrolysis of molten Sodium Hydride liberates Hydrogen, } \\$

$\mathrm{H}_{2} \text { at anode. }$

$2M H \longrightarrow 2M+H_{2} \Uparrow$

$\text {It is a method of preparation of very pure dihydrogen about 99% pure } \\$

Ionic hydrides are frequently used to remove traces of water from organic compounds. What is the underlying basis of this process?

$H^-$ is a strong Bronsted base and hence reacts with

$H_2O$ readily liberating

$H_2$ gas.

$H_2O(l) +H^-(s)\rightarrow H_2(g)+OH^-(aq)$

Complete the following reactions :
(i) $CuO(s) +H_2(g)\rightarrow$
(ii) $CO(g) +H_2(g)\rightarrow$

(I)

$CuO+H_2 \longrightarrow Cu +H_2O$

This is a redox reaction where

$CuO$ is reduced to

$Cu$ and

$H_2$ is oxidised to

$H_2O$

(ii)

$CO+2H_2$

$\longrightarrow$

$CH_3OH$

Properties	$H_2O$	$D_2O$
Melting point K	$373.0$	$374.4$
Enthalpy of vaporization at $(373K)/kj\,mol^{-1}$	$40.66$	$41.61$
Viscosity/centipoise	$0.8903$	$1.107$

Hydrogen - Class 11 Medical Chemistry - Extra Questions

State three uses of water vapour in the air.

How would you confirm that a colourless liquid given to you is pure water? (AS1)(AS_1)

Molecular mass of water is _______ a.m.u.

Name three metals which do not react with water, under normal conditions.

Water exists in a liquid state over a wide range of temperature 0^o0^oC to 100^o100^oC. Explain.

What is the chemical composition of water? Give its molecular formula.

What is the difference between 2H2H or H_{2}H_{2}.

In which group hydrogen is placed on the basis of electronic configuration?

H_{2}O_{2}H_{2}O_{2} solutions are stored in dark-colored plastic or wax-coated glass vessels often with negative catalysts such as urea or sodium stannate added as stabilizers.State whether the given reaction is True or False?

As many as _________ different combination of water are possible from _1H^1, _1H^2, _1H^3_1H^1, _1H^2, _1H^3 and _8O^{16}, _8O^{17}_8O^{16}, _8O^{17} and _8O^{18}_8O^{18}.

Which gas is usually liberated when an acid reacts with a metal ?

Give the properties of water responsible for controlling the temperature of our body.

________ is oxidation number of hydrogen in NaH.

Explain the resemblance of hydrogen to the other members of its group.

The properties of water are different from the properties of the elements of which it is formed. Discuss.

What is the effect on litmus if it is introduced in pure water ?

Which property of water enables it to modify the climate ?

What is the composition of water? In what volume are its two constituent combined?

State the position of hydrogen in the periodic table.

Comment on the dual position of hydrogen in the periodic table

Why is aluminium metal not used in the lab preparation of hydrogen?

Hydrogen is collected by downward displacement of water and not of air, even though it is lighter than air. Explain why?

What is the physical state of water at 257^0C257^0C?

Why does ice float on water ?

What is the physical state of water at 100^{\circ}C100^{\circ}C?

What is the physical state of water at 0^{\circ}C0^{\circ}C?

Explain why apparatus for laboratory preparation of hydrogen should be air tight and away from a naked flame?

Why is sodium metal not used in the lab preparation of hydrogen?

Deionised water is obtained in ion exchange method.If this is true enter 1, if false enter 0.

In exchange process, H_2S H_2S gas is passed through cold water, the hydrogen atoms in H_2SH_2S exchange with deuterium from D_2OD_2O present in water. Thus, H_2SH_2S becomes D_2SD_2S.If this is true enter 1, if false enter 0.

How can the production of dihydrogen, obtained from coal gasification, be increased?

What do you understand by (i) electron-deficient, (ii) electron-precise, and (iii) electron-rich compounds of hydrogen?

What characteristics do you except from an electron-deficient hydride with respect to its structure and chemical reactions?

Justify the position of hydrogen in the periodic table on the basis of its electronic configuration.

Saline hydrides are known to react with water violently producing fire. Can CO_2CO_2, a well known fire extinguisher, be used in this case? Explain.

Complete the following chemical reaction and classify into (a) hydrolysis, (b) redox and (c) hydration reaction. AlCl_3\, (g)\, +\, H_2O\, (l)\, \rightarrowAlCl_3\, (g)\, +\, H_2O\, (l)\, \rightarrow

What do you understand by the term 'auto-protolysis' of water? What is its significance?

What do you understand by the term non-stoichiometric hydrides? Do you expect this type of the hydrides to be formed by alkali metals? Justify your answer.

Among NH_3NH_3, H_2OH_2O and HFHF, which would you expect to have highest magnitude of hydrogen bonding and why?

Complete the following chemical reaction and classify the into (a) hydrolysis, (b) redox and (c) hydration reactions.CaO\, (s)\, +\, H_2O\, (g)\, \rightarrowCaO\, (s)\, +\, H_2O\, (g)\, \rightarrow

How do you expect the metallic hydrides to be useful for hydrogen storage? Explain.

Do you expect the carbon hydrides of the type (C_nH_{2n\, +\, 2})(C_nH_{2n\, +\, 2}) to act as Lewis acid or base? Justify your answer.

Compare the structures of H_2OH_2O and H_2O_2H_2O_2.

What is the difference between the terms hydrolysis and hydration?

Explain syngas in detail.

Complete the following chemical reaction and classify into (a) hydrolysis, (b) redox and (c) hydration reactions. Ca_3N_2\, (s)\, +\, H_2O\, (l)\, \rightarrowCa_3N_2\, (s)\, +\, H_2O\, (l)\, \rightarrow

Write chemical reactions to show the amphoteric nature of water.

Describe the structure of the common form of ice.

How aquatic animals survive is cold countries when temperature fall below 0^{\circ}C0^{\circ}C?

As oxygen is ______ soluble in water, air dissolved in water contains a higher percentage of oxygen (30 - 3530 - 35%) than ordinary air (2121%).

Pure water is a _______ conductor of electricity.

Match the Column-I with Column-II:

Magnesium reacts with steam to form ________ and ________.

As we go up the mountains, the boiling point of water decreases. Why?

Water containing impurities doesn't freeze at 00. Explain?

Water bodies like sea, rivers etc., which are deep appear blue. Why?

Water is tasteless, but we experience different tastes of water in different places. Why?

Write the uses of dihydrogen gas:

Describe an experiment to prove that water is transparent.

Explain the method of preparation of hydrogen gas in laboratory with chemical equation and diagram?

Excess of KIKI and dil. H_{2}SO_{4}dil. H_{2}SO_{4} were mixed in 50\ mL\ H_{2}O_{2}50\ mL\ H_{2}O_{2}. The liberated I_{2}I_{2} required 20\ mL20\ mL of 0.1\ N\ Na_{2}S_{2}O_{3}0.1\ N\ Na_{2}S_{2}O_{3}. Find out the strength of H_{2}O_{2}H_{2}O_{2} in g\ per\ litreg\ per\ litre.

How many moles of H_2O_2H_2O_2 are present in 2 litres of 6.8% w/v H_2O_2H_2O_2 solution?

Calculate percentage of water of crystallization in : Mg\ SO_7H_2OMg\ SO_7H_2O [Atomic masses of Mg= 24, S=32, O=16, H=1]Mg= 24, S=32, O=16, H=1]

Consider the reaction between Zn and dilute hydrochloric acid forming zinc chloride and liberating hydrogen.

Explain the method of preparation of hydrogen gas in laboratory with chemical equation and diagram.

Why Hydrogen although lighter than air, is not collected by the downwards displacement of air?

Why is Hydrogen placed in group II of the modern periodic table ?

Why is distilled water considered to be the purest form of water?

Why does water have higher boiling point than alcohol? At what temperature in kelvin, it can be change into solid state and into vapours?

Why does hydrogen resemble both group II and group 1717 elements ?

Why ice is lighter than water?

Water is a good fire extinguisher. But it is not used extinguish electrical fires and oil for?

Explain the position of hydrogen in the periodic table on the basis of its electronic configuration.

Physical properties of ice, water and steam are different. What is the chemical composition of water in all the three states?

In order to decompose 9 g water 142.5 kJ heat is required. Hence, the enthalpy of formation of water is:

When water boils the temperature remains constant. Give reasons.

2H_22H_2 is needed to make one molecule of water, here '2H_2''2H_2' means:

How do you expect the metallic hydrides to be useful for hydrogen storage? Explain.

Hydrogen is not a metal but it has been assigned aplace in the reactivity series of metals.Explain.

How would you confirm that a colourless liquid given to you is pure water? $(AS_1)$

Water exists in a liquid state over a wide range of temperature $0^o$ C to $100^o$ C. Explain.

What is the difference between $2H$ or $H_{2}$ .

$H_{2}O_{2}$ solutions are stored in dark-colored plastic or wax-coated glass vessels often with negative catalysts such as urea or sodium stannate added as stabilizers.

State whether the given reaction is True or False?

As many as _________ different combination of water are possible from $_1H^1, _1H^2, _1H^3$ and $_8O^{16}, _8O^{17}$ and $_8O^{18}$ .

What is the physical state of water at $257^0C$ ?

$100^{\circ}C$ ?

$0^{\circ}C$ ?

Deionised water is obtained in ion exchange method.
If this is true enter 1, if false enter 0.

Thus, $H_2S$ becomes $D_2S$ .
If this is true enter 1, if false enter 0.

Saline hydrides are known to react with water violently producing fire. Can $CO_2$ , a well known fire extinguisher, be used in this case? Explain.

Complete the following chemical reaction and classify into (a) hydrolysis, (b) redox and (c) hydration reaction.
$AlCl_3\, (g)\, +\, H_2O\, (l)\, \rightarrow$

Among $NH_3$ , $H_2O$ and $HF$ , which would you expect to have highest magnitude of hydrogen bonding and why?

Complete the following chemical reaction and classify the into (a) hydrolysis, (b) redox and (c) hydration reactions.
$CaO\, (s)\, +\, H_2O\, (g)\, \rightarrow$

Do you expect the carbon hydrides of the type $(C_nH_{2n\, +\, 2})$ to act as Lewis acid or base? Justify your answer.

Compare the structures of $H_2O$ and $H_2O_2$ .

Complete the following chemical reaction and classify into (a) hydrolysis, (b) redox and (c) hydration reactions.
$Ca_3N_2\, (s)\, +\, H_2O\, (l)\, \rightarrow$

How aquatic animals survive is cold countries when temperature fall below $0^{\circ}C$ ?

As oxygen is ______ soluble in water, air dissolved in water contains a higher percentage of oxygen ( $30 - 35$ %) than ordinary air ( $21$ %).

Magnesium reacts with steam to form and .

Water containing impurities doesn't freeze at $0$ . Explain?

Excess of $KI$ and $dil. H_{2}SO_{4}$ were mixed in $50\ mL\ H_{2}O_{2}$ . The liberated $I_{2}$ required $20\ mL$ of $0.1\ N\ Na_{2}S_{2}O_{3}$ . Find out the strength of $H_{2}O_{2}$ in $g\ per\ litre$ .

How many moles of $H_2O_2$ are present in 2 litres of 6.8% w/v $H_2O_2$ solution?

Calculate percentage of water of crystallization in : $Mg\ SO_7H_2O$ [Atomic masses of $Mg= 24, S=32, O=16, H=1]$

Why is Hydrogen placed in group $I$ of the modern periodic table ?

Why does hydrogen resemble both group $I$ and group $17$ elements ?

$2H_2$ is needed to make one molecule of water, here $'2H_2'$ means:

Among $PCl_3, CH_{3}^{+}, NH_{2}^{-}$ and $NF_3$ , ......... is least reactive towards water.

Answer the following:
(a) Name a process by which hydrogen gas is manufactured.
(b) Give equation for the reaction.
(c) How is hydrogen seperated from carbon dioxide and carbon monoxide?

As many as...... different combination of water are possible form
$_{1}H^{1}, _{1}H^{2},_{1}H^{3}$ and $_{8}O^{16},_{8}O^{17},_{8}O^{18}$

What is the physical state of water at :
(a) $25^oC$
(b) $0^oC$
(c) $100^oC$ ?

Fill in the blanks :
............... is the purest form of natural water.

Fill in the blanks :
Water has .............. density and .............. volume at $4^0C$ .

Explain why $H_{2}$ and $O_{2}$ do not react at room temperature.

These metal combines H to give white crystalline ionic hydrides of the general of the formula $MH$ .
The tendency to form their hydrides, basic character and stability decreases from Li to Cs since the electropositive character decreases from $Cs$ to $Li$ .

An ice cube at $0^oC$ is placed in some liquid water at $0^oC$ , the ice cube sinks - why?
Discuss the three types of Covalent hydrides

Give the name and formula of the compounds as indicated in the following statement.
A compound of calcium and hydrogen which is used as a portable source of hydrogen for filling balloons.

Answer the following:
What is autoprotolysis of water?

Give the $pH$ of $D_2O$ and $H_2O$ at $298\ K$ .

Answer the following :
Name the chemical compound used in the preparation of $H_2O_2$ by auto- oxidation.

Give an example in which $H_2O$ acts as reducing agent.

Answer the following :
What type of hydrides are formed by the elements having low electronegativity?

Answer the following :
Why $D_2O$ has more density than $H_2O$ ?

Mention the condition in which the following statement is true.
Hydrogen can be prepared from water at ordinary temperature.

Answer the following :
In which group of the periodic table, hydrogen is placed?

What happens when water reacts with the following compounds?

Antimony chloride $(SbCl_3)$ , bismuth chloride $(BiCl_3)$

What happens when?
Water is added to aluminium nitride.

What happens when water reacts with the following compounds?
Red hot iron

Answer the following:
What is plumbosolvency?

Answer the following question:
What happens when $F_{2}$ reacts with water?

A sample of water under study was found to boil at $102^{\circ}C$ at normal pressure. Is the water pure? Will this water freeze at $0^{\circ}C$ ? Comment.

Melting point, enthalpy of vapourisation and viscosity data of $H_2O$ and $D_2O$ is given below:
On the basis of this data explain in which of these liquids intermolecular forces are stronger?

Complete the following reactions
(i) $O_{2}^{2-}+H_{2} O \rightarrow$

Complete the following reactions
(ii) $O_{2}^{-}+H_{2} O \rightarrow$

Name:
A chemical called oxygenated water.

What is the effect on boiling point of water when
(a) pressure is increased
(b) impurity is added

Water has density and _ volume at $4^{0}C$ .

Why sea water does not freeze at $0^{0}C$ ?