Class 7 Acids-Bases-Salts Questions-Answers

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Short Type Questions.

1. Define indicator. Name three indicators.

Ans: The indicator is a substance that shows the acidic or basic nature of a substance by a change in its colour.
Litmus, China rose and Phenolphthalein

2. Give three uses of mineral acids.

2.Ans: We use mineral acid in our daily life. The three uses of mineral acids are:-
 (i) hydrochloric acid is used in cleaning kitchen sinks and bathroom sanitary ware (like wash basin and toilets etc.).
(ii) Sulphuric acid is used in making storage batteries for cars, buses, trucks and inverters.
(iii) Goldsmiths use nitric acids for cleaning gold and silver ornaments.

3. Give three basic differences between acid and bases.

Differences between Acids and Bases

Acids Bases
1. Acids have a sour
1. Bases have a bitter
2. Acids are not
soapy to touch.
2. Bases feel soapy
to touch.
3. Acid turns blue
litmus to red.
3. Bases turn red
litmus to blue.

4. What do you mean by neutralization reaction?

Ans:  The reaction in which an acid reacts with a base to form salt and water. Heat is also evolved during this process and this heat is termed as the heat of neutralisation. A neutralisation reaction can be represented as :
Acid + Base Salt + Water
In a Neutralisation reaction, two new substances, salt and water, are formed. The salt formed during a neutralisation reaction depends on which acid and which base are reacting with each other.

5. What happens when an ant stings? What is its remedy?

Ans:. Ants have formic acid in their sting. So when an ant bites a person, it injects an acidic liquid into the skin of the person. This causes painful irritation and swelling. The effect of an acid can be neutralized by rubbing a mild base like baking soda solution (or calamine lotion) on the stung area on the skin. This is because, being a base, baking soda solution neutralizes the acidic liquid injected by the ant and cancels its effect.

6. What material should be added to a soil which is too acidic? How does this material help in reducing the acidic nature of the soil?
Ans:  When soil becomes acidic, it is treated with bases such as quicklime (calcium oxide) or slaked lime (calcium hydroxide). Bases like quicklime (or slaked lime) neutralize the action of excess acid present in the soil. Thus, a farmer should add bases like quicklime under acidic conditions of the soil.

7. What are the three types of salts? Give one example of each type of salt.

7.Ans: Three types of salts are :
(i) Neutral salts, example Sodium chloride (NaCl)
(ii) Acidic salts, example sodium carbonate (Na2CO3)
(iii) Basic salts, example sodium sulphate (Na2 SO4)

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Class 7 Science NCERT SOLutions and Additional Questions answers