Lesson: Acids, Bases and Salts

Question: 1

What happens when a solution of an acid is mixed with a solution of a base in a test tube?

(i) The temperature of the solution increases

(ii) The temperature of the solution decreases

(iii) The temperature of the solution remains the same

(iv) Salt formation takes place

(a) (i) only

(b) (i) and (iii)

(d) (i) and (iv)

Solution:

(d)

Question:2

An aqueous solution turns red litmus solution blue. Excess addition of which of the following solution would reverse the change?

(a) Baking powder

(b) Lime

(d) Hydrochloric acid

Solution:

(d)

Question:3

During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to

(a) Absorb the evolved gas

(b) Moisten the gas

(d) Absorb $C l^{-}$ ions from the evolved gas

Solution:

(c)

Question: 4

Which of the following salts does not contain water of crystallisation?

(a) Blue vitriol

(b) Baking soda

(d) Gypsum

Solution:

(b)

Question: 5

Sodium carbonate is a basic salt because it is a salt of

(a) Strong acid and strong base

(b) Weak acid and weak base

(d) Weak acid and strong base

Solution:

(d)

Question:6

Calcium phosphate is present in tooth enamel. Its nature is

(a) Basic

(b) Acidic

(d) Amphoteric

Solution:

(a)

Question:7

A sample of soil is mixed with water and allowed to settle. The clear supernatant solution turns the pH paper yellowish-orange. Which of the following would change the colour of this pH paper to greenish-blue?

(a) Lemon juice

(b) Vinegar

(d) An antacid

Solution:

(d)

Question: 8

Which of the following gives the correct increasing order of acidic strength?

(a) Water < Acetic acid < Hydrochloric acid

(b) Water < Hydrochloric acid < Acetic acid

(d) Hydrochloric acid < Water < Acetic acid

Solution:

(a)

Question: 9

If a few drops of a concentrated acid accidentally spills over the hand of a student, what should be done?

(a) Wash the hand with saline solution

(b) Wash the hand immediately with plenty of water and apply a paste of sodium hydrogen carbonate.

(d) Neutralise the acid with a strong alkali.

Solution:

(b)

Question: 10

Sodium hydrogen carbonate when added to acetic acid evolves a gas. Which of the following statements are true about the gas evolved?

(i) It turns lime water milky.

(ii) It extinguishes a burning splinter.

(iii) It dissolves in a solution of sodium hydroxide.

(iv) It has a pungent odour.

(a) (i) and (ii)

(b) (i), (ii) and (iii)

(d) (i) and (iv)

Solution:

(b)

Question: 11

Common salt besides being used in kitchen can also be used as the raw material for making

(i) Washing soda

(ii) Bleaching powder

(iii) Baking soda

(iv) Slaked lime

(a) (i) and (ii)

(b) (i), (ii) and (iv)

(d) (i), (iii) and (iv)

Solution:

(c)

Question: 12

One of the constituents of baking powder is sodium hydrogen carbonate, the other constituent is

(a) Hydrochloric acid

(b) Tartaric acid

(d) Sulphuric acid

Solution:

(b)

Question: 13

To protect tooth decay, we are advised to brush our teeth regularly. The nature of the toothpastes commonly used is

(a) Acidic

(b) Neutral

(d) Corrosive

Solution:

(c)

Question: 14

Which of the following statements is correct about an aqueous solution of an acid and of a base?

(i) Higher the pH, stronger the acid

(ii) Higher the pH, weaker the acid

(iii) Lower the pH, stronger the base

(iv) Lower the pH, weaker the base

(a) (i) and (iii)

(b) (ii) and (iii)

(d) (ii) and (iv)

Solution:

(d)

Question: 15

The pH of the gastric juices released during digestion is

(a) Less than 7

(b) More than 7

(d) Equal to 0

Solution:

(a)

Question: 16

Which of the following phenomena occur, when a small amount of acid is added to water?

(i) Ionisation

(ii) Neutralisation

(iii) Dilution

(iv) Salt formation

(a) (i) and (ii)

(b) (i) and (iii)

(d) (ii) and (iv)

Solution:

(b)

Question: 17

Which one of the following can be used as an acid $-$ base indicator by a visually impaired student?

(a) Litmus

(b) Turmeric

(d) Petunia leaves

Solution:

(c)

Question: 18

Which of the following substance will not give carbon dioxide on treatment with dilute acid?

(a) Marble

(b) Limestone

(d) Lime

Solution:

(d)

Question: 19

Which of the following is acidic in nature?

(a) Lime juice

(b) Human blood

(d) Antacid

Solution:

(a)

Question: 20

In an attempt to demonstrate electrical conductivity through an electrolyte, the following apparatus (Figure) was set up. Which among the following statement(s) is(are) correct?

(i) Bulb will not glow because electrolyte is not acidic

(ii) Bulb will glow because $N a O H$ is a strong base and furnishes ions for conduction.

(iii) Bulb will not glow because circuit is incomplete

(iv) Bulb will not glow because it depends upon the type of electrolytic solution

(a) (i) and (iii)

(b) (ii) and (iv)

Solution:

(c)

Question: 21

Which of the following is used for dissolution of gold?

(a) Hydrochloric acid

(b) Sulphuric acid

(d) Aqua regia

Solution:

(d)

Question: 22

Which of the following is not a mineral acid?

(a) Hydrochloric acid

(b) Citric acid

(d) Nitric acid

Solution:

(b)

Question: 23

Which among the following is not a base?

(a) $N a O H$

(b) $K O H$

(d) $C_{2} H_{5} O H$

Solution:

(d)

Question: 24

Which of the following statements is not correct?

(a) All metal carbonates react with acid to give a salt, water and carbon dioxide

(b) All metal oxides react with water to give salt and acid

(d) Some non-metal oxides react with water to form an acid

Solution:

(b)

Question: 25

Match the chemical substances given in Column (A) with their appropriate application given in Column (B)

Column (A)	Column (B)
(A) Bleaching powder	(i) Preparation of glass
(B) Baking soda	(ii) Production of $H_{2}$ and $C l_{2}$
(C) Washing soda	(iii) Decolourisation
(D) Sodium chloride	(iv) Antacid

(a) A $—$ (ii), B $—$ (i), C $—$ (iv), D $—$ (iii)

(b) A $—$ (iii), B $—$ (ii), C $—$ (iv), D $—$ (i)

(d) A $—$ (ii), B $—$ (iv), C $—$ (i), D $—$ (iii)

Solution:

(c)

Question: 26

Equal volumes of hydrochloric acid and sodium hydroxide solutions of same concentration are mixed and the pH of the resulting solution is checked with a pH paper. What would be the colour obtained? (You may use colour guide given in Figure)

(a) Red

(b) Yellow

(d) Blue

Solution:

(c)

Question: 27

Which of the following is(are) true when $H C l (g)$ is passed through water?

(i) It does not ionise in the solution as it is a covalent compound.

(ii) It ionises in the solution

(iii) It gives both hydrogen and hydroxyl ion in the solution

(iv) It forms hydronium ion in the solution due to the combination of hydrogen ion with water molecule

(a) (i) only

(b) (iii) only

(d) (iii) and (iv)

Solution:

(c)

Question: 28

Which of the following statements is true for acids?

(a) Bitter and change red litmus to blue.

(b) Sour and change red litmus to blue.

(d) Bitter and change blue litmus to red.

Solution:

(c)

Question: 29

Which of the following are present in a dilute aqueous solution of hydrochloric acid?

a) $H_{3} O^{+} + C l^{-}$

b) $H_{3} O^{+} + O H^{-}$

c) $C l^{-} + O H^{-}$

d) $U n i o n i s e d H C l$

Solution:

(a)

Question: 30

Identify the correct representation of reaction occurring during chloralkali process.

a) $2 N a C l (l) + 2 H_{2} O (l) \to 2 N a O H (l) + C l_{2} (g) + H_{2} (g)$

b) $2 N a C l (a q) + 2 H_{2} O (a q) \to 2 N a O H (a q) + C l_{2} (g) + H_{2} (g)$

c) $2 N a C l (a q) + 2 H_{2} O (l) \to 2 N a O H (a q) + C l_{2} (a q) + H_{2} (a q)$

d) $2 N a C l (a q) + 2 H_{2} O (l) \to 2 N a O H (a q) + C l_{2} (g) + H_{2} (g)$

Solution:

(d)

Question: 31

Match the acids given in Column (A) with their correct source given in Column (B).

Column (A)	Column (B)
a) Lactic acid	i) Tomato
b) Acetic acid	ii) Lemon
c) Citric acid	iii) Vinegar
d) Oxalic acid	iv) Curd

Solution:

(a) $—$ (iv)

(b) $—$ (iii)

(d) $—$ (i)

Question: 32

Match the important chemicals given in Column (A) with the chemical formulae given in Column (B).

Column (A)	Column (B)
a) Plaster of Paris	i) $C a {(O H)}_{2}$
b) Gypsum	ii) $C a S O_{4} . \frac{1}{2} H_{2} O$
c) Bleaching Powder	iii)
d) Slaked Lime	iv) $C a O C l_{2}$

Solution: $C a S O_{4} .2 H_{2} O$

(a) $—$ (ii)

(b) $—$ (iii)

(d) $—$ (i)

Question: 33

What will be the action of the following substances on litmus paper? Dry gas, Moistened $N H_{3}$ gas, Lemon juice, carbonated soft drink, Curd, Soap solution. $H C l$

Solution:

Substance	Action on Litmus paper
Dry $H C l$ gas	No change
Moistened $N H_{3}$ gas	Turns red to blue
Lemon juice	Turns blue to red
Carbonated soft drink	Turns blue to red
Curd	Turns blue to red
Soap solution	Turns red to blue

Question: 34

Name the acid present in ant sting and give its chemical formula. Also give the common method to get relief from the discomfort caused by the ant sting.

Solution:

The acid present in ant sting is methanoic acid (formic acid) and its chemical formula is $H C O O H$ .

The ant’s sting can be neutralised by rubbing a mild basic like baking soda $(N a H C O_{3})$ on the affected area.

Question: 35

What happens when nitric acid is added to egg shell?

Solution:

When nitric acid is added to egg shell, it reacts with calcium carbonate present in the egg shell to give carbon dioxide, calcium nitrate, and water. The reaction can be given as:

$C a C O_{3} + 2 H N O_{3} \to C a {(N O_{3})}_{2} + H_{2} O + C O_{2}$

Question: 36

A student prepared solutions of (i) an acid and (ii) a base in two separate beakers. She forgot to label the solutions and litmus paper is not available in the laboratory. Since both the solutions are colourless, how will she distinguish between the two?

Solution:

The student can distinguish between the two solutions by using chemical indicator like phenolphthalein or natural indicators like turmeric, china rose etc.

	In acidic solution	In basic solution
Phenolphthalein	Colourless	Fuchsia
Turmeric	Yellow	Bright red
China rose	Dark pink	Green

Question: 37

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

Solution:

The chemical formula of baking powder is sodium hydrogen carbonate $(N a H C O_{3})$ and that of washing soda is sodium carbonate $(N a_{2} C O_{3} .10 H_{2} O)$ .

On heating, sodium hydrogen carbonate produces $C O_{2}$ gas. $C O_{2}$ turns lime water milky.

$2 N a H C O_{3} \overset{H e a t}{\to} N a_{2} C O_{3} + H_{2} O + C O_{2}$

On heating sodium carbonate, the following reaction takes place.

$N a_{2} C O_{3} .10 H_{2} O \overset{H e a t}{\to} N a_{2} C O_{3} + 10 H_{2} O$

In this case, no such gas is obtained from sodium carbonate.

Question: 38

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.

Solution:

Salt A is baking powder $(N a H C O_{3})$ or sodium hydrogen carbonate. It is commonly used in bakery products.

Salt B, which is used for removal of hardness in water, is sodium carbonate.

When sodium hydrogen carbonate is heated, sodium carbonate $(N a_{2} C O_{3})$ is formed. In the process, $C O_{2}$ gas is released. When $C O_{2}$ gas is passed through lime water, it turns the lime water milky.

The balanced equation for this heating is

$2 N a H C O_{3} \overset{H e a t}{\to} N a_{2} C O_{3} + H_{2} O + C O_{2}$

Therefore,

A is $N a H C O_{3}$

B is ${Na}_{2} {CO}_{3}$

C is ${CO}_{2}$ gas.

Question: 39

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

Solution:

Sodium chloride is used in the manufacture of sodium hydroxide. In this process, chlorine and hydrogen gases are formed as by-products along with sodium hydroxide.

When chlorine gas reacts with lime water, it forms calcium oxychloride, which is used as a bleaching agent in chemical industries.

$\begin{array}{l} 2 N a C l (a q) + 2 H_{2} O (l) \to 2 N a O H (a q) + C l_{2} (g) + H_{2} (g) \\ C a {(O H)}_{2} (s) + C l_{2} (g) \to C a O C l_{2} (s) + H_{2} O \end{array}$

Therefore,

X is chlorine gas

Y is calcium oxychloride (bleaching powder)

Question: 40

Fill in the missing data in the following table

Name of the salt	Formula	Salt obtained from
Name of the salt	Formula	Base	Acid
(i)Ammonium chloride	$N H_{4} C l$	$N H_{4} O H$	$—$
(ii)Copper sulphate	$—$	$—$	$H_{2} S O_{4}$
(iii)Sodium chloride	$N a C l$	$N a O H$	$—$
(iv)Magnesium nitrate	$M g {(N O_{3})}_{2}$	$—$	$H N O_{3}$
(v)Potassium sulphate	$K_{2} S O_{4}$	$—$	$—$
(vi)Calcium nitrate	$C a {(N O_{3})}_{2}$	$C a {(O H)}_{2}$	$—$

Solution:

Name of the salt	Formula	Salt obtained from
Name of the salt	Formula	Base	Acid
(i) Ammonium chloride	$N H_{4} C l$	$N H_{4} O H$	$H C l$
(ii) Copper sulphate	$C u S O_{4}$	$C u {(O H)}_{2}$	$H_{2} S O_{4}$
(iii) Sodium chloride	$N a C l$	$N a O H$	$H C l$
(iv) Magnesium nitrate	$M g {(N O_{3})}_{2}$	$M g {(O H)}_{2}$	$H N O_{3}$
(v) Potassium sulphate	$K_{2} S O_{4}$	$K O H$	$H_{2} S O_{4}$
(vi) Calcium nitrate	$C a {(N O_{3})}_{2}$	$C a {(O H)}_{2}$	$H N O_{3}$

Question: 41

What are strong and weak acids? In the following list of acids, separate strong acids from weak acids.

Hydrochloric acid, citric acid, acetic acid, nitric acid, formic acid, sulphuric acid.

Solution:

Strong acids:

In aqueous solutions, strong acids ionise completely and provide hydronium ions.

Examples: Hydrochloric acid, sulphuric acid, nitric acid.

Weak acids:

Weak acids do not ionize completely in aqueous solutions.

Examples: Citric acid, acetic acid, formic acid.

Question: 42

When zinc metal is treated with a dilute solution of a strong acid, a gas is evolved, which is utilised in the hydrogenation of oil. Name the gas evolved. Write the chemical equation of the reaction involved and also write a test to detect the gas formed.

Solution:

When zinc metal is treated with a dilute solution of a strong acid, it forms salt and hydrogen gas. The hydrogen gas is utilized in the hydrogenation of oil. Therefore, the evolved gas is hydrogen.

$Z n + 2 H C l \to Z n C l_{2} + H_{2}$

Test to detect the hydrogen gas: When a burning candle is brought near the mouth of the test tube containing hydrogen gas, it burns with a pop sound which confirms the presence of hydrogen gas.

Question: 43

In the following schematic diagram for the preparation of hydrogen gas as shown in the given below Figure, what would happen if following changes are made?

(a) In place of zinc granules, same amount of zinc dust is taken in the test tube

(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken

(d) Sodium hydroxide is taken in place of dilute sulphuric acid and the tube is heated.

Solution:

a) If zinc dust is used, hydrogen gas will evolve faster than in case of zinc granules.

b) Almost the same amount of hydrogen gas is evolved when dilute hydrochloric acid is taken instead of dilute sulphuric acid.

$Z n + 2 H C l \to Z n C l_{2} + H_{2} O$

c) Copper does not react with dilute acids in normal condition because copper is less reactive. Thus, if copper turnings are taken in place of zinc, no reaction will take place.

d) If sodium hydroxide is taken in place of sulphuric acid, sodium zincate will be formed and hydrogen gas will be evolved.

$Z n + 2 N a O H \to N a_{2} Z n O_{2} + H_{2}$

Question: 44

For making cake, baking powder is taken. If at home your mother uses baking soda instead of baking powder in cake,

(a) How will it affect the taste of the cake and why?

(b) How can baking soda be converted into baking powder?

Solution:

(a) The chemical name of baking soda is sodium bicarbonate or sodium hydrogen carbonate. On heating, it converts into sodium carbonate which is bitter in taste.

$2 N a H C O_{3} \overset{H e a t}{\to} N a_{2} C O_{3} + H_{2} O + C O_{2}$

Thus, if baking soda is used, the cake will taste slightly bitter.

(b) Baking soda can be converted into baking powder by adding tartaric acid to it.

Question: 45

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, a gas G that is obtained at 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.

Solution:

On reacting with hydrochloric acid, calcium carbonate gives carbon dioxide gas.

$C a C O_{3} + 2 H C l \to C a C l_{2} + C O_{2} + H_{2} O$

When carbon dioxide, so formed, is passed through lime water, the lime water

turns milky because of the formation of calcium carbonate.

$C a {(O H)}_{2} + C O_{2} \to C a C O_{3} + H_{2} O$

The gas evolved at the anode during electrolysis of brine is chlorine.

When passed through dry calcium hydroxide, chlorine gas produces bleaching powder. This is used for disinfecting drinking water.

$C a {(O H)}_{2} + C l_{2} \to C a O C l_{2} + H_{2} O$

Therefore,

X is calcium carbonate

Y is lime water

G is chlorine gas

Y is dry calcium hydroxide

Z is bleaching powder.

Question: 46

A dry pellet of a common base B, when kept in open absorbs moisture and turns sticky. The compound is also a by $-$ product of chloralkali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide? Write a balanced chemical equation for one such solution.

Solution:

Sodium hydroxide $(N a O H)$ is a commonly used base. It absorbs moisture from the atmosphere and becomes sticky.

The acidic oxides react with base to give salt and water.

The reaction between $N a O H$ and $C O_{2}$ can be given as:

$2 N a O H + C O_{2} \to N a_{2} C O_{3} + H_{2} O$

Question: 47

A sulphate salt of Group 2 element of the Periodic Table is a white, soft substance, which can be moulded into different shapes by making its dough. When this compound is left in open for some time, it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt and why does it show such a behaviour? Give the reaction involved.

Solution:

The sulphate salt discussed here is Plaster of Paris $(C a S O_{4} . \frac{1}{2} H_{2} O) .$

The two formula units of $C a S O_{4}$ share one molecule of water. As a result, it is soft.

When it is left for some time in the open, it absorbs moisture from the atmosphere and forms a hard, solid mass of gypsum.

Reaction involved:

$C a S O_{4} . \frac{1}{2} H_{2} O + 1 \frac{1}{2} H_{2} O \to C a S O_{4} .2 H_{2} O$

Question: 48

Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formulae of A, B and C.

Solution:

$\begin{array}{l} 2 N a O H + Z n \to N a_{2} Z n O_{2} + H_{2} \\ N a O H + H C l \to N a C l + H_{2} O \\ N a O H + C H_{3} C O O H \to C H_{3} C O O N a + H_{2} O \end{array}$

Therefore,

X is $N a O H$ (Sodium hydroxide)

A is $N a_{2} Z n O_{2}$ (Sodium zincate)

B is $N a C l$ (Sodium chloride)

C is $C H_{3} C O O N a$ (Sodium acetate).