MCQ Questions for Class 11 Medical Chemistry Equilibrium Quiz 5

Calculate :

${K}_{a}$ for

$HCN$ given

${K}_{b}({CN}^{-})=2.5\times {10}^{-5}$

0%
${10}^{-5}$
0%
$2\times {10}^{-7}$
0%
$4\times {10}^{-10}$
0%
None of these

Explanation

$\displaystyle HCN \rightleftharpoons H^+ + CN^-$ ......(1)

$\displaystyle CN^- + H_2O \rightleftharpoons HCN + OH^- \: \: \: \: \: K_b = 2.5 \times 10^{-5}$ ......(2)

$\displaystyle H_2O \rightleftharpoons H^+ + OH^- \: \: \: \: \: K_w = 1 \times 10^{-14}$ ......(3)
Substract equations (3) from (2), we get

$\displaystyle CN^- +OH^{-} \rightleftharpoons HCN \: \: \: \: \: \frac {K_b}{K_w}= \frac {1}{K_a}$

$\displaystyle \dfrac {2.5 \times 10^{-5}}{1 \times 10^{-14}} = \dfrac {1}{K_a}$

$\displaystyle K_a = 4 \times 10^{-10}$

Assertion: The value of

${K_w}$ increases with increase in temperature.

Reason: Water dissociates more as temperature increases.

0%
Both Assertion and Reason are true and Reason is the correct explanation of Assertion
0%
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
0%
Assertion is true but Reason is false
0%
Assertion is false but Reason is true
0%
Both Assertion and Reason are false

Explanation

$K_w= [H^+][OH^-]$
As the temperature increases, the dissociation of water increases.
Hence, the hydrogen ion concentration and hydroxide ion concentration increases.
Hence, the value of Kw increases with increase in temperature.

Calculate change in concentration of

${H}^{+}$ ion in one litre of water,when temperature changes from

$298K$ to

$310K$ . [Given

${K}_{w}(298)={10}^{-14}, {K}_{w}(310)=2.56\times {10}^{-14}]$ .

0%
$0.3\times {10}^{-7}$
0%
$0.6\times {10}^{-7}$
0%
$1.2\times {10}^{-7}$
0%
$12\times {10}^{-9}$

Explanation

$K_w = [H^+][OH^-]$ and

$[H^+] = [OH^-]$

So at 300 K

$[H^+] = \sqrt {K_w} = 10^{-7}$

At 310 K

$[H^+] = \sqrt {K_w} = 1.6\times10^{-7}$

So change in conc. of hydrogen ion

$[H^+] = 0.6\times10^{-7}$

What is the

$K_b$ for

$NH_2$ group in glycine?

0%
$4\times 10^{-3}$
0%
$1.6\times 10^{-10}$
0%
$6.25\times 10^{-5}$
0%
$2.5\times 10^{-12}$

Explanation

We know,

$k_b = \dfrac {k_w}{k_a} =\dfrac {1 \times 10^{-14}}{1.6 \times 10^{-10}}=6.25 \times 10^{-5}$

Hence, the

$K_b$ for

$NH_2$ group in glycine is

$6.25 \times 10^{-5}$ .

Assertion: The buffer HCOOH/HCOONa will have pH lesser than 7.

Reason: Conjugate base of a weak acid is a strong base.

0%
Both Assertion and Reason are true and Reason is the correct explanation of Assertion
0%
Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
0%
Assertion is true but Reason is false
0%
Assertion is false but Reason is true
0%
Both Assertion and Reason are false

An equimolar solution of

${NaNO_2}$ and

${HNO_2}$ can act as a:

0%
strong reductant
0%
strong oxidant
0%
buffer solution
0%
none of these

Explanation

${HNO_2}$ is a weak acid.

${NaNO_2}$ is a salt of weak acid

${HNO_2}$ with strong base

$NaOH$ .
Hence, an equimolar solution of

${HNO_2}$ and

${NaNO_2}$ acts as a buffer solution.

The ionization constant of water is related to ionic product as:

0%
${k_w>k\left [ H_2O \right ]}$
0%
${k_w=k\left [ H_2O \right ]}$
0%
${k_w<\left [ H_2O \right ]}$
0%
none of the above

Explanation

The ionization constant of water is related to ionic product by the expression

${k_w=k\left [ H_2O \right ]}$ .
The ionization constant for water is given by the expression

$K= \frac {[H^+][OH^-]}{[H_2O]}$ .
Hence,

$K[H_2O] = [H^+][OH^-]$
The ionic product of water is given by the expression

$K_w=[H^+][OH^-]$ .
Hence,

${k_w=k\left [ H_2O \right ]}$ .

${K_a}$ for an acid,

$HA$ is

${1\times 10^{-6}}$ , then

${K_b}$ for

${A^{-}}$ would be:

0%
${10^{-9}}$
0%
${10^{-5}}$
0%
${10^{-8}}$
0%
${10^{-3}}$

Explanation

The acid dissociation equilibrium is as given below:

$HA \rightleftharpoons H^+ + A^-$

$K_a=1\times 10^{-6}$

The base dissociation equilibrium is as follows:

$A^- + H_2O \rightleftharpoons HA + OH^ -$

$K_b=\displaystyle \frac {K_w}{K_a} = \frac {10^{-14}}{10^{-6}}=10^{-8}$

Hence, the correct option is

$\text{C}$

Sulphurous acid turns ________.

0%
blue litmus into red
0%
red litmus into blue
0%
no change to any of the litmus paper
0%
can't say

Explanation

Sulphurous acid

$(H_2SO_3)$ is an acid. The main use of litmus is to test whether a solution is acidic or basic. Blue litmus paper turns red under acidic conditions. So sulphurous acid turns blue litmus into the red.

The following equilibrium is established when hydrogen chloride is dissolved in acetic acid.

$HCl (aq)\,+\, CH_3COOH(aq)\, \rightleftharpoons \,Cl^-(aq)\,+\,CH_3\,COOH_2(aq)$

The set that characterizes the conjugate acid-base pairs is

0%
$(HCl,\, CH_3COOH)\, and\, (CH_3COOH_2,\, Cl^-)$
0%
$(HCl,\, CH_3COOH_2)\, and\, (CH_3COOH,\, Cl^-)$
0%
$(CH_2COOH_2,\, HCl)\, and\, (Cl^-,\, CH_3COOH)$
0%
$(HCl,\, Cl^-)\, and\, (CH_3\,COO^-,\, CH_3COOH)$

Explanation

The conjugate base of an acid is formed when the acid donates a proton

$(H^+)$ .

$HCl$ (acid) looses

$H^+$ to form its conjugate base,

$Cl^-$

And

$CH_3COOH$ (acid) looses

$H^+$ to form its conjugate base,

$CH_3COO^-$

Hence the conjugate acid-base pair here is

$(HCl, Cl^-)\; and\; (CH_3COOH, CH_3COO^-)$

So, the correct option is

$D$

The chemical that changes its colour when it is left open in sunlight is:

0%
$FeSO_4\, (s)$
0%
$Pb(NO_3)_2\, (s)$
0%
$AgCl\, (s)$
0%
$BaCl_2\, (aq)$

Explanation

$AgCl\, (s)$ colors changes when exposed in sunlight.

_____ of acids are lower than that of bases.

0%
$log[H^+]$
0%
$pOH$
0%
$[H^+]$
0%
$pH$

Explanation

$pH$ of acids are lower than that of bases.

Anything

$pH <7$ is acidic, and anything

$pH>7$ is alkaline or basic.

$pH$ scale range from

$0$ to

$14$ .

Hence, option D is correct.

Which of the following statements is correct for a solution saturated with AgCI and AgBr if their solubilities in moles per litre in separate solutions are x and y respectively?

0%
$[Ag^+]\,=\, x\,+\, y$
0%
$[Ag^+]\,=\, [Br^-]\,+\, [Cl^-]$
0%
$[Br^-]\,=\, y$
0%
$[Cl^-]\,>\, x$

Explanation

For a salt in a solution, the concentration of ions will be in equilibrium. So in the given options
[Ag+]=[Br]+[Cl] since

$Ag$ is common.

Study the table carefully. Which of the above are correctly matched?

0%
(i) & (iii)
0%
(ii) & (iv)
0%
(i), (ii) & (iii)
0%
(i), (iii) & (iv)

Which of the following is correct regarding buffer solution?

0%
It contains weak acid and its conjugate base.
0%
It shows low change in pH on adding small amount of acid or base.
0%
(A) and (B) both
0%
None of these

Which of the following salts on heating gives a mixture of two gases?

0%
$Ba(NO_3)_2$
0%
$NaNO_3$
0%
$KNO_3$
0%
$RbNO_3$

Explanation

$(A)$

$Ba(NO_3)_2$

$Reason$ : The elements in the group 2 includes beryllium(

$Be$ ), magnesium(

$Mg$ ), calcium(

$Ca$ ), strontium(

$Sr$ ), barium(

$Ba$ ) and radium(

$Ra$ ).

The group 2 nitrates, on heating, gives metal oxide, nitrogen dioxide and oxygen gas.

For example -

$2Ba(NO_3)_2(s)$

$\rightarrow$

$2BaO(s)$ +

$4NO_2(g)$ +

$O_2(g)$

Group 2 nitrates also become more thermally stable down the group.

0.5 mmol of

$NaCN$ and 1 mmol of

$HCl$ in 1 L solution is a buffer.

0%
True
0%
False

Explanation

0.5 mmol of

$NaCN$ and 1 mmol of

$HCN$ in 1 L solution is a buffer.

An acid buffer solution contains weak acid (

$HCN$ ) and its salt (

$NaCN$ ) with a strong base (

$NaOH$ ).

State whether the given statement is true or false:

$AgCl$ is less soluble in aqueous sodium chloride solution than in pure water.

0%
True
0%
False

Explanation

$AgCl \rightleftharpoons Ag^+ + Cl^-$

$NaCl \rightarrow Na^+ + Cl^-$

Sodium chloride is a strong electrolyte and is completely dissociated. This increases the chloride ion concentration in solution and suppresses the ionization of AgCl. Hence, the solubility of AgCl decreases.

Neutralization always produces a solution of

pH=7.

0%
True
0%
False

Explanation

$25^o$ C,

$K_w = [H^+][OH^-] = 10^{-7}\times10^{-7} = 10^{-14}$

$pH+pOH=14$ at this temperature.

Neutral solution will have pH = 7.

But as we increase temperature, more water molecules will dissociate and the number of ions will increase. So as we increase the temperature,

$K_w$ increases and

$pH+pOH$ decreases.

So neutral solution will have pH less than 7.

When hydrated

$MgCl_2.\, 6H_2O$ is strongly heated:

0%
$MgO$ is formed
0%
$Mg(OH)_2$ is formed
0%
$Mg(OH)Cl$ is formed
0%
Ahydrous $MgCl_2$ is formed

The dissociation constant of acetic acid at a given temperature is

$1.69\, \times\, 10^{-5}$ . The degree of dissociation of

$0.01\ M$ acetic acid in the presence of

$0.01\ M$

$HCl$ is equal to:

0%
$0.41$
0%
$0.13$
0%
$1.69\, \times\, 10^{-3}$
0%
$0.013$

Explanation

$K=\dfrac{[CH_3COO^-][H^+]}{[CH_3COOH]}$
Here,

$\alpha$ is the degree of dissociation of

$CH_3COOH$ .

$\Rightarrow K = \dfrac{C\alpha [H^+]}{C(1-\alpha)} = \dfrac{\alpha [H^+]}{1-\alpha}$

$HCl$ dissociates completely.

$CH_3COOH$ itself is a weak acid and in the presence of

$HCl$ , its dissociation will be negligible.
Hence,

$[H^+]$ can be approximated to

$[HCl]$ (

$H^+$ ions from acetic acid will be negligible).
As

$\alpha$ is very less, the denominator can be approximated to 1.

$\Rightarrow 1.69\times 10^{-5} = \alpha 0.01$

$\Rightarrow \alpha = \dfrac{1.69\times 10^{-5}}{0.01}=1.69\times 10^{-3}$

What are the products formed when an aqueous solution of magnesium bicarbonate is boiled?

0%
$MgCO_3,\, H_2O,\, CO_2$
0%
$Mg(HCO_3)_2,\, H_2O$
0%
$Mg(OH)_2,\, H_2O$
0%
$Mg,\, CO_2,\, H_2O$

Explanation

When magnesium bicarbonate is boiled

$MgCO_3, H_2O$ and

$CO_2$ are formed. A small amount of

$Mg(OH)_2$ is also formed.

Reaction:

$Mg(HCO_ 3)_2\xrightarrow[\Delta]{} MgCO_ 3+H_ 2O+CO_ 2+Mg(OH)_ 2$

A mixture of aqueous solution of sodium acetate and sodium propanoate forms a buffer solution.

0%
True
0%
False

Explanation

The given statement "A mixture of aqueous solution of sodium acetate and sodium propanoate forms a buffer solution." is false. An acidic buffer solution contains weak acid and its salt with strong base. Following are examples of acidic buffer solutions.

(1)

$\displaystyle CH_3COOH + CH_3COONa$

(2)

$\displaystyle CH_3CH_2COOH + CH_3CH_2COONa$

If we create vacuum in container

$A$ at

$\displaystyle 25^{\circ}C$ then:

0%
water will be completely vaporised in the container
0%
there will be no vaporisation in the container
0%
the equilibrium will establish in between water vapour and liquid $\displaystyle H_{2}O$ and vapour pressure of water will remain same as it would be in presence of atmospheric pressure
0%
the equilibrium in between $\displaystyle H_{2}O\left ( v \right )$ and $H_{2}O\left ( l \right )$ will establish but vapour pressure of $\displaystyle H_{2}O\left ( v \right )$ will be more than as it would be in presence of atmospheric pressure

Explanation

If we create vacuum in container A at

$25^oC$ then the equilibrium will establish in between water vapour and liq

$H_2O$ and vapour pressure of water will remain same as it would be in presence of atmospheric pressure.

Which of the following can give a buffer solution?

0%
$HCI + NaOH$
0%
$CH$ $_3$ $COONa$
0%
$HCOOH + HCOONa$
0%
$H_2SO_4 + Na_2SO_4$

Explanation

Buffer solutions have reserve acidity and reserve basicity. They are a mixture of a weak acid and its salt with a strong base or weak base and its salt with strong acid.

$\therefore$

$HCOOH$ and

$HCOONa$ can from a buffer.

Which of the following properties of a solution of

$NaCl$ will not vary as the concentration of salt is increased?

0%
$pH$
0%
Density
0%
Refractive index
0%
Electrical conductivity

Which of the following statement is correct regarding container B?

0%
Water will migrate from Glass (i) to Glass (ii) and no equilibrium will establish
0%
Water will migrate from Glass (i) to Glass (ii) and equilibrium will establish after some time
0%
Water will not migrate to any side
0%
None of these

Which of the following is/are correct when some

$HCl$ is added to pure water? [Temperature is constant]

0%
${ K }_{ w }$ decreases
0%
Degree of dissociation of water decrease
0%
At new equilibrium $\left[ { H }^{ +} \right] _{ total }>\left[ { OH }^{ - } \right] _{ total }$
0%
Solution remains neutral

Which of the following acids has the smallest dissociation constant?

0%
$CH_3CHFCOOH$
0%
$FCH_2CH_2COOH$
0%
$BrCH_2CH_2COOH$
0%
$CH_3CHBrCOOH$

Explanation

$BrCH_2CH_2COOH$ will have the smallest dissociation constant as here,smaller

$K_a$ weak is the acid.

acetic acid has the lowest inductive effect of attached bromide due to long distance and low electronegativity of Br as compared to other acids where the halide is comparatively nearer or stronger.

F is more electronegative than Br so more -I effect due to F.

(Inductive effect: The effect on electron density in one portion of a molecule due to electron-withdrawing or electron-donating groups elsewhere in the molecule.)

The constituent present in baking powder is:

0%
Sodium benzoate
0%
Acetic acid
0%
Sodium lactate
0%
Tartaric acid

Fill in the blanks with suitable words:

Excessive use of fertilizers makes the soil ______ so it should be treated with ______ like ________. If the soil is ____ then the organic matter should be added to it.

0%
basic, acids, formic acid, acidic
0%
basic, acids, milk of magnesia, neutral
0%
acidic, bases, zinc carbonate, neutral
0%
acidic, bases, slaked lime, basic

Explanation

Fertilizers contain the maximum amount of mineral acids so they increase the acidity of soils and it can be neutralized by the addition of calcium hydroxide or other basic chemicals. On the other hand, alkaline soils with high

$pH$ content are neutralized by the addition of organic matter content in the soil.

Which property is common between vinegar and curd?

0%
Sweet taste
0%
Bitter taste
0%
Tasteless
0%
Sour taste

A solution of ferric chloride in water is acidic to litmus due to:

0%
hydrolysis
0%
decomposition
0%
electrolysis
0%
condensation

Explanation

When ferric chloride is dissolved in water the solution becomes acidic as a result of hydrolysis. The chemical reaction, in words and formulae are: Basically, ferric chloride in water solution ionizes to iron (ferric) and chloride ions, whilst the water ionizes to hydrogen and hydroxide ions;

$FeCl_3\rightarrow Fe^{3+} + 3Cl^-$

$H_2O \rightarrow H^+ + OH^-$

The ferric ions will partially combine with the hydrogen and hydroxide ions to form the ferric hydroxide, a compound that is only slightly soluble and precipitates from solution as a brown solid.

$Fe^{3+} + 3OH^-\rightarrow Fe(OH)_3$

This precipitation can be regarded as removing hydroxyl ions from the solution, leaving a relative excess of hydrogen ions and it is this excess of hydrogen ions that makes the solution acidic.

So the answer is

$A$ .

Identify the correct option amongst the following:

Electropositive atoms tend to form :

0%
negative ions
0%
positive ions
0%
covalent bonds
0%
metallic bonds

Explanation

Electropositive elements tend to lose electrons and form positive ions e.g. univalent alkali metals

${ Li }^{ + },{ Na }^{ + },{ K }^{ + }$ and divalent alkaline earth metals

${ Be }^{ 2+ },{ Mg }^{ 2+ }$

Which one of the following substance will be most suitable for cutting a very hard material?

0%
Silicon carbide
0%
Lead
0%
Zinc metal
0%
Sodium chloride crystal

Arrange the following in order of increasing

$pH$ ?

0%
Water < Blood < Soda water
0%
Water < Soda water < Blood
0%
Soda water < Water < Blood
0%
Soda water < Blood < Water

Explanation

$pH$ of the solution is a measure of hydronium or hydrogen ion concentration in a solution.

Higher is the hydrogen ion concentration lower is the $pH$ of the solution and the solution will be acidic. $pH$ range of acidic solution is $0-6.9$
Lower is the hydrogen ion concentration, higher will be the $pH$ and solution will be basic. $pH$ of the basic solution ranges from $7.1-14$
A solution having $pH$ $7$ is neutral.

Soda water is carbonated water so it has carbon dioxide present in it which reacts with water and form carbonic acid, therefore, it is acidic in nature having

$pH$ between 3-4. The

$pH$ of water is neutral i.e.

$7$ , while blood is alkaline in nature therefore its

$pH$ , will be above

$7$ and in the range of

$7.35-7.4$

The function of 'buffer solution' is:

0%
to increase the pH value in chemical reaction
0%
to decrease the pH value on chemical reaction
0%
to increase or decrease the pH value of according the need
0%
to keep the pH value constante in chemical reaction

Explanation

A buffer solution is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa. Its

$pH$ changes very little when a small or moderate amount of strong acid or base is added to it and thus it is used to prevent changes in the

$pH$ of a solution.

So answer is D.

Which one of the following statements is true?

0%
All alkalis are bases
0%
Rusting is a combination of iron with oxygen dissolved in water
0%
Heavy water accelerates the growth of living organisms, plants and animals
0%
Sodium carbonate is used as a baking powder

Explanation

All alkalis are bases.

Rusting is a slow action of air and moisture which degrades the metal.

Heavy water inhibits the growth of living organisms.

Sodium carbonate is washing powder.

So, option

$A$ is correct.

If a salt after rubbing with fingers gives the smell of ammonia, then the salt is:

0%
ammonium chloride
0%
sodium carbonate
0%
calcium carbonate
0%
lead sulphide

Explanation

If a salt after rubbing with fingers, gives the smell of ammonia, then the salt may be ammonium chloride.
After rubbing, due to warming, ammonium chloride may decompose to give ammonia and hydrogen chloride.

$\displaystyle NH_4Cl \xrightarrow {warm} NH_3 + HCl$

Which of the following methods is not used for preparing a salt?

0%
Reaction between an acid and a base
0%
Action of acid on metals
0%
Action of acid on metal oxides
0%
Dissolution of acids in water

$pH$ of tomato juice is 4, that means it is:

0%
basic
0%
acidic
0%
neutral
0%
none of these

Explanation

The

$pH$ of tomato juice is 4, which is less than 7 and so is acidic. Generally, a substance with

$pH$ more than 7 is considered basic in nature.

The original colour of a salt is black. When it is heated its colour is changed from black to red. The salt may be:

0%
zinc oxide
0%
mercuric oxide
0%
lead oxide
0%
red lead

Explanation

Mercury(II) oxide, also called mercuric oxide or simply mercury oxide, has a formula of

$HgO$ . It has a red or orange color. Mercury(II) oxide is a solid at room temperature and pressure. It is originally black in colour.

A solution of sodium chloride will:

0%
turn red litmus blue
0%
turn blue litmus red
0%
turn red litmus orange
0%
not change the colour of either red or blue litmus

${ pK_b }$ of

${ NH }_{ 3 }$ is 4.74 and

${ pK }_{ b }$ of

${ A }^{ - },{ B }^{ - }$ and

${ C }^{ - }$ are 1, 5 and 6 respectively, aqueous solution of 0.01 M has pH in the increasing order:

0%
${ NH }_{ 4 }A<{ NH }_{ 4 }B<{ NH }_{ 4 }C$
0%
${ NH }_{ 4 }C<{ NH }_{ 4 }B<{ NH }_{ 4 }A$
0%
${ NH }_{ 4 }C<{ NH }_{ 4 }A<{ NH }_{ 4 }B$
0%
All have equal $pH$

Acetic acid is used for preservation of foods.

0%
True
0%
False

Sea water contains about 24g of salts dissolved per litre of it.

0%
True
0%
False

Explanation

Approximately for every litre of seawater there is

$35$

$g$ of salt.

Salts are naturally found in seawater and salts are formed in the neutralization reaction.

What could be the nature of aqueous solution of sodium sulphate?

0%
Acidic
0%
Basic
0%
Neutral
0%
Nature depends on the concentration of the solution

Explanation

Sodium sulphate

$Na_2SO_4$ is formed by the neutralization reaction between strong acid (sulphuric acid )

$H_2SO_4$ and strong base (sodium hydroxide)

$NaOH$ .

$NaOH+H_2SO_4 \rightarrow Na_2SO_4+H_2O$

Thus a salt formed by the neutralization reaction between strong acid and strong base is neutral in nature.

Hence, the correct answer is option (C).

Which of the following ions is furnished by acids in aqueous solution?

0%
$OH^-$ ions
0%
$H^+$ ions
0%
$H_3O^+$ ions
0%
None of these

Explanation

Acids are compounds that generally release hydrogen ions

$H^+$ which result in the acidic conditions.

However, in case of aqueous solution, there is presence of water

$(H_2O)$ and hence the hydrogen ion combines with water to form hydronium ion

$H_3O^+$ .

$H^+ + H_2O \rightarrow H_3O^+$

Hence, the correct answer is option (C).

The acid present in tea is:

0%
citric
0%
tannic
0%
formic
0%
lactic

Explanation

Some natural ingredients have some amount of acid present in them due to which they get their unique flavour.

Tea has tannic acid in it, just like citrus fruits have citric acid and tamarinds have tartaric acid.

Hence, the correct answer is an option

$(B)$ .

The loss of water of crystallization to the atmosphere by a compound is termed:

0%
deliquescence
0%
dehydration
0%
efflorescence
0%
hydrolysis

CBSE Questions for Class 11 Medical Chemistry Equilibrium Quiz 5 - MCQExams.com

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Practice Class 11 Medical Chemistry Quiz Questions and Answers

CBSE Questions for Class 11 Medical Chemistry Equilibrium Quiz 5 - MCQExams.com

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Practice Class 11 Medical Chemistry Quiz Questions and Answers

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