Chapter 2: Acids Bases and Salts

1. A solution turns red litmus blue, its pH is likely to be
(a) 1
(b) 4
(c) 5
(d) 10
Solution : (d) 10

2. A solution reacts with crushed egg-shells to give a gas that turns lime-water milky. The solution contains
(a) NaCl
(b) HCl
(c) LiCl
(d) KCl
Solution : (b) The solution contains HCI.

3. 10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount HCl solution (the same solution as before) required to neutralise it will be
(a) 4 mL
(b) 8 mL
(c) 12 mL
(d) 16 mL
Solution : (d) 16 mL

4. Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic

Solution : (c) Antacid is used for treating indigestion.

5. Write word equations and then balanced equations for the reaction taking place when –
(a) dilute sulphuric acid reacts with zinc granules.
(b) dilute hydrochloric acid reacts with magnesium ribbon.
(c) dilute sulphuric acid reacts with aluminium powder.
(d) dilute hydrochloric acid reacts with iron filings.

Solution :
(a) Zinc + Sulphuric acid  Zinc sulphate +Hydrogen
H₂SO4(aq) + Zn(s)  ⟶ ZnSO₄(aq) + H₂ (g)
(b) Magnesium +  Sulphuric acid  magnesium chloride +Hydrogen gas
Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
(c) Aluminum + Sulphuric acid  Aluminum sulphate +Hydrogen gas
3H₂SO₄ + 2Al → Al₂(SO₄)₃ + 3H2
(d) Iron + Hydrochloric acid  Iron chloride +Hydrogen
6HCl(aq) + 3Fe(s) → 3FeCl₂(aq) + 3H₂(g)

6. Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an Activity to prove it.
Solution : lcohol and glucose both contain hydrogen but not categorized as acids. This can be proved by following activity.

Material required :- Beaker, nails, battery, connecting wires, bulb, switch and alcohols.
Procedure :
1. Set up the experiment as follows
2. Take ethyl alcohol in the beaker in the beaker.
3. When the switch is turned on, the bulb does not glow.
4. Take glucose solution in place of alcohols but bulb does not glow.

7. Why does distilled water not conduct electricity, whereas rain water does?
Solution : Distilled water is a pure form of water and is devoid of any ionic species. Therefore, it does not conduct electricity. Rain water, being an impure form of water, contains many ionic species such as acids and therefore it conducts electricity.

8. Why do acids not show acidic behaviour in the absence of water?
Solution : Acids do not show acidic behaviour in the absence of water because the dissociation of hydrogen ions from an acid occurs in the presence of water only. It is the hydrogen ions that are responsible for the acidic behaviour.

9. Five solutions A,B,C,D and E when tested with universal indicator showed pH as 4,1,11,7 and 9, respectively. Which solution is
(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration
Solution :
(a) D
(b) C
(c) B
(d) A
(e) E

10. Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH₃COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?
Solution : HCl is stronger acid than CH₃COOH. Therefore, H+ ions concentration in test tube A will be more than that in test tube B. hence, reaction will take place faster in test tube A than in test tube B. so, fizzing will occur more vigorously in test tube B.

11. Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Solution : The pH of milk is 6. As it changes to curd, the pH will reduce because curd is acidic in nature. The acids present in it decrease the PH.

12. A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
(b) Why does this milk take a long time to set as curd?

Solution :
(a) The milkman shifts the pH of the fresh milk from 6 to slightly alkaline because in alkaline condition, milk does not set as curd easily.
(b) Since this milk is slightly basic than usual milk, acids produced to set the curd are neutralized by the base. Therefore, it takes a longer time for the curd to set.

13. Plaster of Paris should be stored in a moisture-proof container. Explain why?
Solution : Plaster of Paris reacts with moisture to form gypsum and sets to a hard mass. Therefore, it should be stored in moisture-proof container.

14. What is a neutralisation reaction? Give two examples.
Solution : A reaction in which an acid and base react with each other to give a salt and water is termed as neutralization reaction. In this reaction, energy is evolved in the form of heat.
For example :- NaOH + HCl ⟶ NaCl+H₂O

(ii) During indigestion (caused due to the production of excess of hydrochloric acid in the stomach), we administer an antacid (generally milk of magnesia, Mg(OH)2 which is basic in nature). The antacid neutralizes the excess of acids and thus gives relief from indigestion.
Mg(OH)₂ + 2HCl → MgCl₂+2H₂O

15. Give two important uses of washing soda and baking soda.
Solution :
Uses of washing soda :
(i) As cleansing agent.
(ii) Removing permanent hardness of water.
(iii) Used in glass, soap and paper industries.
Uses of baking soda :
(i) For making baking powder

(ii) As ingredient of antacid.