Sunday, June 19, 2022

Class 10 Science | Chapter-end Exercise & Answers | 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


Answer:
(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


Answer:
(b) HCl


3.  10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HC1. If we take 20 mL of the same solution of NaOH, the amount of HC1 solution (the same solution as before) required to neutralise it will be

(a) 4 mL       

(b) 8 mL              

(c) 12 mL            

(d) 16 mL


Answer:
(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


Answer:
(c) Antacid


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 filing


Answer:

a)     Zinc + dilute sulphuric acid Zinc sulphate + Hydrogen

Zn (s) + H2SO4 (aq) ZnSO4 (aq) + H2 (g)

b)     Magnesium ribbon + dil. Hydrochloric acid Magnesium chloride + Hydrogen

Mg (s) + 2 HCl (aq) MgCl2 (aq) + H2 (g)

c)     Aluminium powder + dil. Sulphuric acid Aluminium sulphate + Hydrogen

2Al (s) + 3H2SO4 (aq) Al2 (SO4)3 (aq) + 3H2 (g)

d)     Iron filings + Dilute hydrochloric acid Ferric chloride + Hydrogen

2Fe (s) + 6HCl (aq) 2FeCl3 (aq) + 3H2 (g)


6.  Compounds such as alcohol and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.


Answer:

·    Take solutions of alcohols and glucose.

·    Fix two nails on a cork and place it in 100 mL beaker.

·    Connect the nails to the two terminals of a 6 volt battery through a bulb and a switch.

·    Pour alcohol in the beaker and switch on the current.

·    The bulb does not glow.

·    Repeat the experiment with glucose. The bulb does not glow in this case also.

·    It means no ions or H+ ions are present in the solution.

This shows that alcohols and glucose are not acids.


7.   Why does distilled water not conduct electricity, whereas rainwater does?


Answer:
Distilled water does not contain any ionic compound (like acids, bases or salts).

Rainwater contains carbonic acid (H2CO3) formed as a result of reaction with CO2 in atmosphere. Carbonic acid provides hydrogen ions, H+ (aq) to rainwater. Hence the rainwater conducts electricity.


8.   Why do acids not show acidic behaviour in the absence of water?


Answer:

The acidic behaviour is due to the presence of hydrogen ions, [H+ (aq)]. Acid produces H+ ions only in the presence of water. So in the absence of water, an acid will not show 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.

Answer:

(a) D             

(b) C                    

(c) B

(d) A             

(e) E

Increasing order of H+ ion concentration:

11 < 9 < 7 < 4 < 1


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. In which test tube will the fizzing occur more vigorously and why?


Answer:

Fizzing will occur more vigorously in test tube A.

Hydrochloric acid (HCl) is a strong acid and so contains greater amount of H+ ions. But acetic acid (CH3COOH) is a weak acid containing lesser amount of H+ ions.

So fizzing occurs vigorously in test tube A. Fizzing is due to evolution of hydrogen gas.


11.Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.


Answer:

Yes. pH of milk falls below 6 as it turns into curd due to the formation of lactic acid. Lactic acid present reduces its 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?


Answer:

a.  Milk is made slightly alkaline so that it may not get sour easily due to the formation of lactic acid in it.

b.  Because the lactic acid formed has to first neutralise the alkali present in it.


13.Plaster of Paris should be stored in a moisture proof container. Explain why?


Answer:

The moisture causes slow setting of plaster of Paris due to hydration. This makes plaster of Paris useless.


14.What is a neutralisation reaction? Give two examples.


Answer:
It is the reaction between an acid and a base to form salt and water. E.g.

·    NaOH (aq)    +    HCl (aq)       NaCl (aq) + H2O (l)

Sodium hydroxide      Hydrochloric acid        Sodium chloride

·    NaOH (aq) + CH3COOH (aq) CH3COONa + H2O (l)

Sodium hydroxide      Acetic acid                  Sodium acetate


15.Give two important uses of washing soda & baking soda.


Answer:

Uses of washing soda:

(i)    Used in glass, soap and paper industries.

(ii)   To remove permanent hardness of water.

Uses of baking soda:

(i)    Used as an antacid to remove acidity of the stomach.

(ii)    To make baking powder.


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