# NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

Written by Team Trustudies
Updated at 2021-02-11

## NCERT solutions for class 7 Science Chapter 5 Acids Bases Salts Exercise

Q.1 State differences between acids and bases.

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

##### acid
(1) Acids are sour in taste.
(2) Acid turns blue litmus to red (3) Acid is a substance which contain ${{\text{\H}}}^{+}$
##### base
(1) Bases are bitter to taste.
(2) Base turns red litmus to blue
(3) Base is a substance which contain ${{\text{\OH}}}^{?}$

Q.2 Ammonia is found in many household products, such as window cleaners. It turns red litmus blue. What is its nature?

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

Basic in nature

Q.3 Name the source from which litmus solution is obtained. What is the use of this solution?

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

Litmus solution is extracted from lichens. It is used to determine whether the given solution is acidic or basic.

Q.4 Is the distilled water acidic/basic/neutral? How would you verify it?

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

Distilled water is neutral in nature. We can verify it by showing that neither blue nor red litmus paper changes its colour when dipped in it.

Q.5 Describe the process of neutralisation with the help of an example.

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

The reaction between an acid and a base is known as neutralization reaction. In this reaction, both acid and base cancel each other's effect. Neutralisation reaction results in the formation of salt and water. During this reaction, energy in the form of heat is evolved.
Example : NaOH + HCl $?$NaCl + H2O + Heat

Q.6 Mark ‘T’ if the statement is true and ‘F’ if it is false:
(i) Nitric acid turns red litmus blue. (T/F)
(ii) Sodium hydroxide turns blue litmus red. {T/F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
(id) Indicator is a substance which shows different colours in acidic and basic solutions. . (T/F)
(v) Tooth decay is caused by the presence of a base. (T/F)

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

(i) Nitric acid turns red litmus blue. (F)
(ii) Sodium hydroxide turns blue litmus red. {F)
(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T)
(id) Indicator is a substance which shows different colours in acidic and basic solutions. . (T)
(v) Tooth decay is caused by the presence of a base. (F)

Q.7 Dorji has a few bottles of soft drink in his restaurant. But, unfortunately, these are not labelled. He has to serve the drinks on the demand of customers. One customer wants acidic drink, another wants basic and third one wants neutral drink. How will Dorji decide which drink is to be served to whom?

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

Dorji can decide with the help of litmus paper:
(i) If the drink which would turn a red litmus to blue than that is basic in nature.
(ii) If the drink turns a blue litmus to red than that is acidic in nature.
(iii) The drink which would not affect both red and blue litmus would be neutral.

Q.8 Explain why:
(a) An antacid tablet is taken when you suffer from acidity.
(b) Calamine solution is applied on the skin when an ant bites.
(c) Factory waste is neutralised before disposing it into the water bodies.

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

(a) This is because during acidity, an excess of acids is produced in the stomach. An antacid contains base, such as milk of magnesia. These bases react with excess of acids and neutralize their effect, thus giving us relief. (b) When an ant bites, it injects formic acid into the skin. Calamine solution contains zinc carbonate which is basic in nature. Therefore, it is applied on the skin to neutralize the effect of formic acid. (c) Factory wastes contain acids. Therefore, these wastes, when thrown directly to water bodies, harm aquatic lives. Hence, these wastes are neutralised with basic chemicals before disposing to water bodies.

Q.9 Three liquids are given to you. One is hydrochloric acid, another is sodium hydroxide and third is a sugar solution. How will you identify them? You have only turmeric indicator.

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

1. Hydrochloric acid turn Yellow to blue
2. Sodium hydroxide turn Yellow to red
3. Sugar solution No change

Q.10 Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

The solution is basic in nature. Bases change the colour of litmus paper to blue. As the colour of blue litmus paper is not affected, the solution must be basic.

Q.11 Consider the following statements:
(a) Both acids and bases change colour of all indicators. (b) If an indicator gives a colour change with an acid, it does not give a change with a base.
(c) If an indicator changes colour with a base, it does not change colour with an acid.
(d) Change of colour in an acid and a base depends on the type of the indicator.
Which of these statements are correct?
(i) All four
(ii) (a) and (d)
(iii) (b) and (c)
(iv) only (d)

NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts