Class 10 Chemistry - Acids, Bases And Salts

Give one word or phrase for the following statement.
The property by which certain hydrated salts, when left exposed to atmosphere, lose their water of crystallization and crumble into powder.

The water losing property of crystallization when left exposes to atmosphere and crumble into powder is called Efflorescence.

Do acids produce ions only in an aqueous solution? Give reasons for your answer.

$$\bf{Concept-}$$

Mostly all of the acids form hydrogen ions and conjugate bases when dissolved in water.

$$\bf{Explanation-}$$

Acids dissociate in water or aqueous solutions to form ions. These are responsible for the conduction of electricity. Acids don't dissociate hydrogen ions in absence of water. Therefore, we can say that acids produce ions only in aqueous solutions.

Give the reaction of Potassium Hydroxide ($$KOH$$) with water.

$$KOH$$ reacts with water as follows:
$$KOH$$ + $$H_2O$$ -------> $$K^+$$ + $$OH^-$$

Complete the following table:
$$Acid + Base \rightarrow Salt + water$$
$$HNO_3 + .............. \rightarrow KNO_3 + H_2O$$
$$............. +2NH_4OH \rightarrow (NH_4)_2SO_4 + .............$$
$$............. + KOH \rightarrow KBr + .............$$

A neutralisation reaction occurs when an acid and a base react to produce water and a salt
$$Acid + Base \rightarrow Salt + water$$

$$\bullet$$ When nitric acid$$(HNO_3)$$ reacts with potassium hydroxide(KOH), potassium nitrate$$(KNO_3)$$ and water are formed.
$$HNO_3 + KOH\rightarrow KNO_3 + H_2O$$

$$\bullet$$ When sulphuric acid$$(H_2SO_4)$$ reacts with ammonium hydroxide$$(NH_4OH)$$, ammonium sulphate$$[(NH_4)_2SO_4]$$ and water are formed.
$$H_2SO_4 +2NH_4OH \rightarrow (NH_4)_2SO_4 + 2H_2O$$

$$\bullet$$ When hydrogen bromide(HBr) reacts with potassium hydroxide(KOH), potassium bromide(KBr) and water are formed.
$$HBr+ KOH \rightarrow KBr + H_2O$$

Name a salt which does not contain water of crystallization.

Sodium nitrate, potassium chloride, potassium nitrate, etc. are salts which do not contain water of crystallization.

Fill in the following table
Name of the salt Formula Salt obtained from Base Salt obtained from Acid
(i) Ammonium Chloride NH$$_4$$Cl NH$$_4$$OH -
(ii) Copper sulphate - - H$$_2$$SO$$_4$$
(iii) Sodium chloride NaCl NaOH -
(iv) Magnesium Nitrate Mg(NO$$_3$$)$$_2$$ - HNO$$_3$$
(v) Calcium nitrate Ca(NO$$_3$$)$$_2$$ Ca(OH)$$_2$$ -

Name of the salt	Formula	Salt obtained from Base	Salt obtained from Acid
(i) Ammonium Chloride	NH$$_4$$Cl	NH$$_4$$OH	HCl
(ii) Copper sulphate	CuSO$$_4$$	Cu(OH)$$_2$$	H$$_2$$SO$$_4$$
(iii) Sodium chloride	NaCl	NaOH	HCl
(iv) Magnesium Nitrate	Mg(NO$$_3$$)$$_2$$	Mg(OH)$$_2$$	HNO$$_3$$
(v) Calcium nitrate	Ca(NO$$_3$$)$$_2$$	Ca(OH)$$_2$$	HNO$$_3$$

Complete and balance the following chemical reaction:
$$CaCO_{3}+HCl\rightarrow $$

$$\bullet$$ Balanced chemical reaction is,

$$CaCO_3+2HCl\longrightarrow CaCl_2+CO_2+H_2O$$

When calcium carbonate reacts with hydrochloric acid, calcium chloride, carbon dioxide, and water are formed.

Give a suitable chemical term for the following:
A definite number of water molecules bound to a salt.

This is known as the water of crystallization. Water molecules are associated with salt to hydrate anhydrous salt. The water of crystallization also changes the colour of the salt. For example, Hydrated copper sulphate($$CuSO_4.5H_20$$) is bright blue in colour whereas anhydrous copper sulphate($$CuSO_4$$) is white in colour.

Mention the types of solutions based on the $$pH$$ value.

Types of the solution:
(1) Acidic with $$pH$$ less than 7. For example, aqueous solutions of $$HCl$$, $$H_2SO_4$$, acetic acid etc.
(2) Neutral with $$pH$$ 7. For example pure water, aqueous $$NaCl$$ solution.
(3) Basic with pH more than 7. For example, aqueous solutions of $$NaOH$$, $$KOH$$, $$NaHCO_3$$ etc.

Describe the process of neutralization with the help of an example.

$$\bullet$$ The reaction between an acid and a base is known as $$\text{neutralization}$$. Salt and water are produced in this process with the evolution of heat.

$$\text{ Acid + Base} \longrightarrow \text{Salt + Water}$$ $$ \text{ (Heat is evolved)}$$

$$\text{Example:}$$ When hydrochloric acid $$(HCl)$$ reacts with sodium hydroxide $$(NaOH)$$ (base), sodium chloride salt and water are produced.

$$HCl+NaOH \longrightarrow NaCl+ H_2O $$

State one relevant observation for the following.
Anhydrous calcium chloride is exposed to air for some time.

It forms solution (becomes wet) and the process is called deliquescence.

Dry ammonia has no action on litmus paper, but a solution of ammonia in water turns red litmus paper blue. Why?

Dry ammonia does not liberate any ions like $$OH^-$$ as it is not in contact with water, thereby has no action on litmus paper.

Ammonia solution in water turns red litmus blue as it forms ammonium ion ($$NH_4^+$$) and hydroxyl ion ($$OH^-$$).

$$NH_3 +H_2O \rightarrow NH_4^+ +OH^-$$

Here ammonia act as a base by liberating $$OH^-$$ ion. Thus it turns red litmus paper blue. Acidic and basic nature of a substance is because of the formation of $$H^+$$ ions in solution and $$OH^–$$ ions in solution, respectively.

Balance the following equation:
$$Mg(OH)_{2}+HCl \longrightarrow MgCl_{2}+H_{2}O$$

Given reaction: $$Mg\left(OH\right)_{2}+HCl\rightarrow MgCl_{2}+H_{2}O$$

In the above reaction, $$Mg(OH)_2$$ and $$HCl$$ are reactants, and $$Mg Cl_2$$ and $$H_2O$$ are the products.

$$\textbf{Step 1: Count the number of atoms of each element on either side of the reaction}$$

Reactant side	Product side
Mg = 1	Mg = 1
H = 3	H = 2
O = 2	O = 1
Cl = 1	Cl = 2

$$\textbf{Step 2: Multiply HCl in the reactant side by 2}$$

Since one extra chlorine is present on the product side. Thus, multiply HCl by 2 in order to balance the Cl-atoms.

$$Mg\left(OH\right)_{2}+2HCl\rightarrow MgCl_{2}+H_{2}O$$

$$\textbf{Step 3: Balance H and O atoms on both the sides}$$

Now, two extra hydrogen and one extra oxygen atoms are present on the reactant side. Thus, multiply $$H_{2}O$$ on the product side by 2 in order to balance the H and O atoms.

$$Mg\left(OH\right)_{2}+2HCl\rightarrow MgCl_{2}+2H_{2}O$$

Therefore, the balanced chemical equation is

$$Mg\left(OH\right)_{2}+2HCl\rightarrow MgCl_{2}+2H_{2}O$$

State the number of water molecules present in crystals of washing soda and plaster of Paris. What are these molecules called?

The chemical formula of washing soda is $$Na_2CO_3·10H_2O$$

The chemical formula of plaster of Paris is $$CaSO_4. \dfrac{1}{2} H_2O$$

Hence,

No. of water molecules in washing soda$$=10$$

No. of water molecules in plaster of Paris$$=\dfrac{1}{2}$$

$$\therefore$$ These molecules are named as water of crystallization.

Conc. $$H_2SO_4$$ is a good drying agent, yet it is not used to dry $$NH_3$$.

$$\bullet$$ Concentrated sulphuric acid $$(H_2SO_4)$$ is a good drying agent because it has a strong affinity for water $$(H_2O)$$ so it can absorb water very fast.

$$\bullet$$ As ammonia $$(NH_3)$$ has basic nature, concentrated sulphuric acid can quickly react with it and can form another compound. This is the reason conc. $$H_2SO_4$$ is not used to dry $$NH_3$$.

Which colour is shown by a neutral solution on a $$pH$$ scale?

The colour shown by a neutral solution on a $$pH$$ scale is green.

When a solution is added to cloth strip treated with onion extract, then the smell of onion cannot be detected.
State whether the given solution contains an acid or a base.

The given solution contains base because onion extract is one of the olfactory indicators and they either change their smell or lose it when treated with an acid or base and onion loses its smell when it is treated by a base.

When a solution is added to vanilla extract, then the characteristics smell of vanilla cannot be detected.
State whether the given solution is an acid or a base.

The characteristic smell of vanilla is destroyed by basic solutions. So in basic solutions, we cannot detect the smell of vanilla. Whereas, it is retained in an acidic solution. So the given solution is a basic solution.

15ml of water and 10 ml of sulphuric acid are to be mixed in a beaker.

i] State the method that should be followed for mixing with appropriate reasons.
ii] What is this process called?

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Sodium hydrogen carbonate is a basic salt. Justify the statement.

$$\bullet$$ The chemical formula of sodium hydrogen carbonate is $$NaHCO_3$$.

$$\bullet$$ Sodium hydrogen carbonate is a basic salt because it is prepared by the neutralization reaction of sodium hydroxide $$(NaOH)$$, a strong base and carbonic acid $$(H_2CO_3)$$, a weak acid.

$$\bullet$$ The chemical equation for the neutralization reaction between sodium hydroxide and carbonic acid is as follows:

$$NaOH+H_2CO_3\rightarrow NaHCO_3+H_2O$$

$$\textbf{Additional Information:}$$

The neutralization reaction of a strong base and a weak acid produces a basic salt and water.

Which is more basic (or more alkaline)? A solution of pH = 8 or a solution of pH = 11?

Solution of pH = 11 is more basic than pH = 8. More the pH value, more is the basic nature.

Two drinks P and Q gave acidic and alkaline reactions, respectively. One has a pH value of $$9$$ and the other has a pH value of $$3$$. Which drink has a pH value of $$9$$?

Drink Q has a $$pH$$ value of $$9$$. An alkaline solution or basic solution has a $$pH$$ value greater than $$7$$.

Fill in the blanks in the following sentences:
(a) Acids have a ....... taste and they turn ....... litmus to .......
(b) Substances do not show their acidic properties without .......
(c) Acids produce ....... ions on dissolving in water.
(d) Those substances whose smell (or odour) changes in acidic or basic solutions are called .......
(e) Onion and vanilla extract are .......

(a) Acids have a sour taste and they turn blue litmus to red.

(b) Substances do not show their acidic properties without water.

(d) Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators.

(e) Onion and vanilla extract are olfactory indicators.

List the important products of the Chlor-alkali process. Write one important use of each.

The Chlor-alkali process is used in the electrolysis of $$NaCl$$. The important products formed in this process are sodium hydroxide, chlorine, and hydrogen gas.

$$2NaCl + 2H_2O \longrightarrow 2NaOH + Cl_2 + H_2$$

An electric current is passed through the brine to form $$H_2$$ at the cathode and $$Cl_2$$ at the anode, leaving a solution of sodium hydroxide.

Uses:-

$$NaOH$$ - For soaps and detergents.
$$Cl_2$$ - PVC, pesticides.
$$H_2$$ - Fuels, production of $$NH_3$$.

(a) What happens when dilute hydrochloric acid is added to sodium carbonate? Write a balanced chemical equation of the reaction evolved.
(b) Which gas is liberated when dilute hydrochloric acid reacts with sodium carbonate? How will you test for the presence of this gas?

(a) When dilute hydrochloric acid reacts with sodium carbonate, then sodium chloride, carbon dioxide and water are formed.

$$Na_2CO_3 (s) + 2HCl(aq) \rightarrow 2NaCl (aq) + CO_2 (g) + H_2O (l)$$

(b) $$CO_2$$ gas is liberated during the reaction.

When carbon dioxide gas formed in the form of brisk effervescence is passed through lime water, it turns the lime water milky. If excess carbon dioxide gas is passed through the milky lime water, the solution becomes clear again. This confirms the presence of carbon dioxide gas.

What is an olfactory indicator? Name two olfactory indicators. What is the effect of adding sodium hydroxide solution to these olfactory indicators?

Those substances whose smell (or odour) changes in acidic or basic solutions are called olfactory indicators. Onion and vanilla extracts are olfactory indicators.

When a basic solution like sodium hydroxide is added to a cloth strip treated with onions (or onion extract), then the smell of onion vanishes.
And when sodium hydroxide is added to vanilla extract, it destroys the characteristic smell of vanilla.

Which is more acidic: a solution of pH = 2 or a solution of pH = 6?

Solution of pH = 2 is more acidic as lower the pH more is the acidic character.

What happens when an acid reacts with a base? Explain by taking the example of hydrochloric acid and sodium hydroxide. Give the chemical reaction which takes place. What is the special name of such a reaction?

An acid reacts with a base to form salt and water.
Hydrochloric acid reacts with sodium hydroxide solution to form sodium chloride(salt) and water.

$$NaOH (aq) + HCl(aq) \rightarrow NaCl(aq) + H_2O(l)$$

Such a reaction is termed a neutralisation reaction.

Write the name and formula of one salt each which contains:
(a) two molecules of water of crystallisation
(b) five molecules of water of crystallisation
(c) ten molecules of water of crystallisation

(a) Gypsum $$(CaSO_4. 2H_2O)$$ contains two molecules of water of crystallisation.

(b) Copper sulphate crystals $$(CuSO_4. 5H_2O)$$ contains five molecules of water of crystallisation.

Two solutions $$A$$ and $$B$$ have pH of $$5$$ and $$8$$ respectively. Which solution will be basic in nature?

Solutions having a pH greater than 7 are basic in nature. So, here solution $$B$$ is basic.

Arrange the following in the increasing order of acidic strength.
Acetic acid, water and hydrochloric acid

Because hydrochloric acid is a strong acid, acetic acid is a weak acid, and water is neutral, the order is as follows:
Water< acetic acid< hydrochloric acid

(a) What is meant by "water of crystallisation" in a substance? Explain with an example.
(b) How would you show that blue copper sulphate crystals contain water of crystallisation?
(c) Explain how anhydrous copper sulphate can be used to detect the presence of moisture (water) in a liquid.

(a)

Water of crystallization refers to a fixed amount of water that is in a loose chemical combination with one molecule of a salt in its crystal form.

$$\bullet$$ For example, $$CuSO_4.5H_2O$$ (copper sulphate pentahydrate). The dot in the formula denotes a loose chemical combination of water molecules, in which the water molecules can be eliminated.

$$\bullet$$ Salts which contain water of crystallization are called hydrated salts.

(b)

To show blue copper suphate crystals contain water of crystallization, following observation is described:

$$\bullet$$ When copper sulphate crystals (chemical formula $$CuSO_4.5H_2O$$) are heated strongly, they lose all the water of crystallisation and form anhydrous copper sulphate ($$CuSO_4$$), which is white.

$$\bullet$$ As the blue colour of the crystals disappeared on heating, we can conclude that the colour was due to the water of crystallisation.

$$\bullet$$ This proves that blue copper sulphate crystals contain water of crystallisation.

$$CuSO_4.5H_2O \to CuSO_4 + 5H_2O$$

(c)

Anhydrous copper sulphate can be used to detect the presence of moisture in a liquid:

$$\bullet$$ Anhydrous copper sulphate turns blue on adding water.

$$\bullet$$ This property of anhydrous copper sulphate is used to detect the presence of moisture in a liquid.

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

White colour Blue colour

Which of the following salt has a blue colour and why?
$$CuSO_4.5H_2O$$ or $$ CuSO_4.$$

$$CuSO_4.5H_2O$$ salt has a blue colour.

The blue colour of $$CuSO_4.5H_2O$$ salt is due to the presence of water of crystallization. The water molecules which form part of the structure of a crystal are called water of crystallization. The water of crystallization gives the crystal of salts their shape and colour.

How many molecules of water of crystallization (per formula unit) are present in:
(a) copper sulfate crystals?
(b) washing soda?
(c) gypsum?

(a) Copper sulfate crystals $$(CuSO_4. 5H_2O)$$ contain five molecules of water of crystallization.

(b) Sodium carbonate crystal or washing soda $$(Na_2CO_3. 10H_2O)$$ contains ten molecules of water of crystallization.

The pH values of five solutions A, B, C, D and E are given below:
A 1
B 5
C 7
D 11
E 13

Which solution is:
weakly alkaline
neutral
strongly acidic
strongly alkaline, and
weakly acidic?

The lesser the pH value more acidic is the solution and the higher the pH value more alkaline is the solution.

1. Weakly alkaline: D (pH = 11)

2. Neutral: C (pH = 7)

3. Strongly acidic: A (pH = 1)

4. Strongly alkaline: E (pH = 13)

5. Weakly acidic: B (pH = 5)

What is an olfactory indicator? Name two such indicators.

Those substances whose smell (or odour) changes in acidic or basic solution are called olfactory indicators. Onion and vanilla extract are two examples of olfactory indicators.

Fill in the blanks:

Sodium hydroxide or potassium hydroxide is found in ________.

Sodium hydroxide or potassium hydroxide is found in soap.

Sodium hydroxide, also called caustic soda or lye, is a traditional ingredient for soap-making. While potassium hydroxide is more common in liquid soap-making, it is possible to produce liquid soaps using caustic soda.

A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, when a gas G obtained at the anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identity X, Y, G, and Z.

$$\textbf{Concept:}$$ Bleaching powder is produced by the reaction of calcium hydroxide with chlorine. Calcium hydroxide is also known as slaked lime. When chlorine gas is passed over the dry slaked lime thus bleaching powder and water is produced.

$$\bullet$$When calcium carbonate reacts with hydrochloric acid, it gives carbon dioxide gas.

$$\mathrm{CaCO}_{3}+2 \mathrm{HCl} \rightarrow \mathrm{CaCl}_{2}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}$$

$$\bullet$$When carbon dioxide is passed through limewater, the limewater turns milky. This happens because of the formation of calcium carbonate.

$$\mathrm{CO}_{2}+\mathrm{Ca}(\mathrm{OH})_{2} \rightarrow \mathrm{CaCO}_{3}+\mathrm{H}_{2} \mathrm{O}$$

$$\bullet$$On electrolysis of brine, chlorine gas is obtained at the anode. When chlorine gas is passed through limewater, it gives bleaching powder.

$$\mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{Cl}_{2} \rightarrow \mathrm{CaOCl}_{2}+\mathrm{H}_{2} \mathrm{O}$$

$$\bullet$$X is calcium carbonate. Y is limewater. G is chlorine. Z is bleaching powder.

How would you distinguish between baking powder and washing soda by heating?

When baking powder is heated, carbon dioxide is produced. This can be shown by following equation.

$$2 \mathrm{NaHCO}_{3}+\mathrm{Heat} \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}$$

Evolution of carbon dioxide can be confirmed by passing the gas into lime water. if limewater turns milky, it indicates evolution of carbon dioxide gas. This reaction does not happen when washing soda is heated.

In one of the industrial processes used for the manufacture of sodium hydroxide, a gas X is formed as a by-product. The gas X reacts with lime water to give a compound Y which is used as a bleaching agent in the chemical industry. Identify X and Y giving the chemical equation of the reactions involved.

Sodium chloride is subjected to chloralkali process to manufacture sodium hydroxide. Chlorine and hydrogen gas are formed during this process.

$$2 \mathrm{NaCl}+2 \mathrm{H}_{2} \mathrm{O} \rightarrow 2 \mathrm{NaOH}+\mathrm{Cl}_{2}+\mathrm{H}_{2}$$

Chlorine reacts with lime water to give bleaching powder.

$$\mathrm{Ca}(\mathrm{OH})_{2}+\mathrm{Cl}_{2} \rightarrow \mathrm{CaOCl}_{2}+\mathrm{H}_{2} \mathrm{O}$$

X is chlorine. Y is bleaching powder.

Salt A commonly used in bakery products on heating gets converted into another salt B which itself is used for removal of hardness of water and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B, and C.

Salt A is sodium hydrogen carbonate (baking soda). When it is heated, it turns into sodium carbonate; Baking soda is obtained by the reaction of brine with carbon dioxide and ammonia.
This is known as the Solvay process.

$$\mathrm{NaCl}+\mathrm{CO}_{2}+\mathrm{NH}_{3}+\mathrm{H}_{2} \mathrm{O} \rightarrow \mathrm{NH}_{4} \mathrm{Cl}+\mathrm{NaHCO}_{3}$$

In this process, calcium carbonate is used as the source of $$CO_{2}$$, and the resultant calcium oxide is used to recover ammonia from ammonium chloride.which is salt B. In this reaction, carbon dioxide gas is also produced; which is the gas C.

$$2 \mathrm{NaHCO}_{3}+\mathrm{Heat} \rightarrow \mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O}$$
Sodium hydrogen carbonate is used in bakery products. Sodium carbonate is used for removing the hardness of water.

Classify the following as physical or chemical property
Most metal oxides form alkalis on interacting with water.

Chemical property of metallic oxides: Metallic oxides react with water and form alkalies.

Water turns the colour of anhydrous copper sulphate to _______.

Answer is $$blue$$.

Fill in the blanks :
The number of molecules of water of crystallization in washing soda is .........

Formula for washing soda is $$Na_2CO_3.10H_2O$$
The number of molecules of water of crystallization in washing soda is $$ 10 $$

What are salts?

The substance formed (in addition to water) when acid and base react with each other is called salt. Examples: Sodium sulphate, copper sulphate, sodium chloride, sodium nitrate, and sodium carbonate.

$$Acid + Base \rightarrow {Salt + Water} $$

Give the $$pH$$ value of pure water. Does it change if common salt is added to it?

$$pH$$ of pure water is 7 at $$ 25^{\circ} C $$. No, the pH does not change when common salt is added because common salt is neutral in nature.

What would you observe when red litmus paper is introduced in a sodium carbonate solution?

Sodium carbonate when dissolved in water forms a weak acid, carbonic acid and a strong base sodium hydroxide. Hence the overall solution is basic in nature. Hence, red litmus paper introduced to a sodium carbonate solution will turn blue.

Write the name, method of production and uses of following:
$$NaOH$$

Name: Sodium hydroxide

Method of production: This is made by chlor-alkali process. An aqueous solution of sodium chloride(brine) is electrolyzed to obtain $$NaOH$$.

$$2 NaCl+2H_2O\xrightarrow{electrolysis} 2NaOH+Cl_2+H_2$$

Uses: It is used for making paper, soap, detergents, and artificial fibres.

What are olfactory indicators? Give examples.

Olfactory indicators are the substances whose odour changes in acidic or basic media.

Example: Vanilla extract, onion.

Take $$5mL$$ water in a test tube and slowly add concentrated sulphuric acid to it. Touch the bottom of the test tube. What do you feel? Is the reaction exothermic or endothermic?

The bottom of the test tube feels hot because it is an exothermic reaction.

A student heated a few crystals of copper sulphate in a dry boiling tube.
(a) What will be the colour of the copper sulphate after heating?
b) Will you notice water droplets in the boiling tube?
(c) Where do these water droplets come from?
(d) After adding $$2-3$$ drops of water on the sample of copper sulphate obtained after heating. What do you observe? Is the blue colour of copper sulphate restored?

a) White

b) Yes

c) Copper sulphate crystals that seem to be dry contain water of crystallization ($$CuSO_4.5H_2O$$) which on heating gets lost. Hence, we get white coloured anhydrous crystals ($$CuSO_4$$) and water droplets on the test tube.

(i) Dry pellets of a base ‘$$X$$’ when kept in open, absorb moisture and turn sticky. The compound is also formed by chlor-alkali process. Write the chemical name and formula of X. Describe chlor-alkali process with a balanced chemical equation. Name the type of reaction that occurs when X is treated with dilute hydrochloric acid. Write the chemical equation.
(ii) While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?

(i) $$X$$ is sodium hydroxide ($$NaOH$$)
When sodium chloride solution (brine solution) is electrolysed, sodium hydroxide solution is formed $$H_2$$ and $$Cl_2$$ gases are liberated. this is chlor-alkali process.
$$2NaCl+2H_2O\xrightarrow{electrolysis}2NaOH+H_2+Cl_2$$

$$NaOH+HCl\rightarrow NaCl+H_2O$$
$$'X'$$
The above reaction is the neutralization reaction
(ii) It is because the process of dilution is highly exothermic. If the water is added to the acid, the amount of heat released can cause a lot of damage.

Hydrated calcium sulphate has the formula of $$CaSO_{4}.2H_{2}O$$.
(i) What is the name given to the water molecules present in the salt?
(ii) Calculate the percentage of water molecules in hydrated calcium sulphate.
[Ca = 40; S = 32; O = 16; H = 1]

$$\textbf{Part (1): Name of the water molecules present in the salt}$$

The chemical name of hydrated calcium sulphate $$(CaSO_{4}.2H_{2}O)$$ is calcium sulphate dihydrate. It is commonly known as Gypsum. The name given to the water molecules present in calcium sulphate salt is the "water of crystallization".

$$\textbf{Part (2): Percentage of water molecules in hydrated calcium sulphate}$$

The molecular mass of $$CaSO_{4}.2H_{2}O$$ can be calculated as,

$$\begin{align*}CaS{O_4}.2{H_2}O &= (1 \times Ca) + (1 \times S) + (4 \times O) + (4 \times H) + (2 \times O)\\ &= (1 \times 40) + (1 \times 32) + (4 \times 16) + (4 \times 1) + (2 \times 16)\\ &= 40 + 32 + 64 + 4 + 32\\ &= 172\end{align*}$$

The molecular mass of water of crystallization present in salt can be calculated as,

$$\begin{align*}2{H_2}O &= 2\left( {2 \times H + 1 \times O} \right)\\ &= 2\left( {2 + 16} \right)\\ &= 36\end{align*}$$

The percentage of water molecules in hydrated calcium sulphate can be calculated as shown below.

$$\begin{align*}\% \;of\;water\;of\;crystallization &= \dfrac{{Mass\,of\;water}}{{Total\;mass\;of\;hydrated\;salt}} \times 100\% \\ &= \dfrac{{36}}{{172}} \times 100\% \\ &= 20.93\% \end{align*}$$

Therefore, the percentage of water molecules in hydrated calcium sulphate is $$20.93\ \%.$$

A cloth strip dipped in onion juice is used for testing a liguid $$\mathrm{X}$$. The liquid '$$\mathrm{X}$$' changes its odour. Which type of an indicator is onion juice? The liquid '$$\mathrm{X}$$' turns blue litmus red. List the observations the liquid '$$\mathrm{X}$$'
will show on reacting with the following:
(a) Zinc granules
(b) Solid sodium carbonate
Write the chemical equations for the reactions involved.

$$\bullet$$ Onion juice is an olfactory indicator.

$$\bullet$$ As liquid $$'X'$$ turns blue litmus red, and hence it is acidic in nature.

(a) When liquid $$'X'$$(acid) reacts with zinc granules(metal), it produces salt with the evolution of colourless and odourless hydrogen gas.

$$Acid + Zn\rightarrow Salt + H_2(g)$$

(b) When liquid $$'X'$$(acid) reacts with solid sodium carbonate, it produces salt and water along with the production of colourless and odourless carbon dioxide gas.

$$Acid + Na_2CO_3(s)\rightarrow Salt + H_2O(l) + CO_2(g)$$

$$\text{Additional information}$$

$$\bullet$$ Olfactory indicators are those indicators that change their smell rather than their colour to help determine whether a given solution is acidic or basic.

$$\bullet$$ An acidic solution turns the blue litmus paper red

$$\bullet$$ The basic solution turns the red litmus paper blue.

Bleaching powder is produced when chlorine reacts with?

Answer: dry slaked lime, $$Ca(OH)_2$$

Bleaching powder ($$CaOCl_2$$) is produced when chlorine reacts with dry slaked lime $$[Ca(OH)_2]$$.

$$Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$$

The products obtained in a neutralization reaction of an acid and a base are .......... and water.

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Read the information given in the table and answer the following questions.
Solution
pH Value
Reaction with Phenolphthalein solution
Reaction with Methyl orange solution
HCl
1
No colour change.
Turns into red
Distilled water
7
No colour change. No colour change.
NaOH
13
Turns into pink colour.
Turns into yellow colour.
Lemon juice
2.5
No colour change. Turns into red colour.
NaCl
7
No colour change. No colour change.
Baking Soda
8
Turns into pink colour.
Turns into yellow colour.
(a) List out the acids in the above table.
(b) What is the nature of the solution which gives pink colour with Phenolphthalein solution?
(c) List out the neutral solutions in the above table.
(d) Name the strongest acid and the strongest base among the given solutions.

(a) Acids are HCl and lemon juice because the pH is less than 7.

(b) Alkaline or basic solution turns phenolphthalein pink.

(d) HCl is the strongest acid and NaOH is the strongest base.

What is meant by water of crystallization of a substance? Describe an activity to show the water of crystallization.

Water of crystallization or the water of hydration is the water that occurs in the crystals. It is denoted as hydrated compound $$nH_2O $$. For example, gypsum is a soft mass having the formula $$ CaSO_4.2H_2O$$. On heating gypsum, plaster of paris is formed by losing the water of crystallization. Plaster of paris is a hard mass with the formula $$ CaSO_4.\dfrac{1}{2}H_2O$$.

Name the four chemicals that are obtained from common salt and write their molecular formulae.

Chemicals are:

1) Sodium hydroxide. $$(NaOH)$$

2) Baking soda ( $$NaHCO_3$$)

3) Washing soda ( $$Na_2CO_3. 10H_2O $$ )

4) Bleaching powder ($$ CaOCl_2$$).

Oxide of a metal M was water-soluble.
When a blue litmus strip was dipped in this solution, it did not undergo any change in its colour, Predict and explain the nature of oxide.

The metal oxide is basic in nature as blue litmus does not undergo any change in colour in the basic medium.
The metal oxide dissolves in water to give a basic metal hydroxide solution, hence the nature of the metal oxide is basic.

Write the name, method of production and uses of $$NaHCO_3$$.

$$\text{Name:}$$ Sodium bicarbonate or baking soda

$$\text{Method of Production:}$$ It is made by the reaction between sodium chloride, ammonia, carbon dioxide and water.

$$NaCl+H_2O+NH_3+CO_2\rightarrow NH_4Cl+NaHCO_3$$

$$\text{Uses}$$: It is used as an antacid, in soda-acid fire extinguisher and for making baking powder.

Give the properties and uses of bleaching powder.

Chlorine is produced during the electrolysis of aqueous sodium chloride (brine). This chlorine gas is used for the manufacture of bleaching powder. Bleaching powder is produced by the action of chlorine on dry slaked lime [Ca(OH)2]. Bleaching powder is represented as $$CaOCl_2$$.

It's uses are:

$$(i)$$ Bleaching powder used in bleaching cotton, wood pulp, clothes.

$$(ii)$$ Oxidising agent used in chemical industries.

$$(iii)$$ Disinfectant to kill germs in drinking water.

Solution	pH Value	Reaction with Phenolphthalein solution	Reaction with Methyl orange solution
HCl	1	No colour change.	Turns into red
Distilled water	7	No colour change.	No colour change.
NaOH	13	Turns into pink colour.	Turns into yellow colour.
Lemon juice	2.5	No colour change.	Turns into red colour.
NaCl	7	No colour change.	No colour change.
Baking Soda	8	Turns into pink colour.	Turns into yellow colour.

Acids, Bases And Salts - Class 10 Chemistry - Extra Questions

Give one word or phrase for the following statement.The property by which certain hydrated salts, when left exposed to atmosphere, lose their water of crystallization and crumble into powder.