NCERT Solutions for Class 7 science Chapter 5

Acids, Bases and Salts

NCERT Solutions for Class 7 Science chapter 5 Exercise Question

Question 1

State differences between acids and bases.

Answer

Question 2

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

Answer

The basic in nature

Question 3

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

Answer

Litmus solution is extracted from lichens. It is used as an indicator find whether it acidic or basic nature of a solution.

Question 4

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

Answer

Distilled water is neutral , and this can be verify by using red and blue litmus paper because it not changes its colour when dipped in it.

Question 5

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

Answer

The reaction between an acid and a base are called neutralisation . For example
when hydrochloric acid(acid) and sodium hydroxide(base) react they form sodium chloride(salt) and water. heat also evolved.

Question 6

Mark ‘T’ if the statement is true and ‘F’ if it is false:

(i) Nitric acid turn 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)

(iv) 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)

Answer

i) False

ii) False

iii) True

iv True

v) False

Question 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?

Answer

Dorji can decide with the help of litmus paper. The drink which would turn a red litmus to blue would be basic. If the drink turns a blue litmus to red would be acidic. The drink which would not affect both red and blue litmus would be neutral.

Question 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.

Answer

a)The antacid tablet contains base like milk of magnesia which neutralises the acid produced in the stomach.

b)Ant injects formic acid inside the skin on biting. Calamine solution consists of Zinc carbonate which is basic in nature which neutralises the acid produced by ant in skin .

c)Factory wastes are acidic in nature which may cause harm to the aquatic life.So base are useing to neutralised the acid before disposing it into the water bodies.

Question 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.

Answer

Name of the substances effect on turmeric indicator.
1. If turmeric indicator turn Yellow to blue then the substance Hydrochloric acid.
2. If turmeric indicator turn Yellow to red then the substance Sodium hydroxide .
3. If turmeric indicator turn No change then the substance Sugar solution

Question 10

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

Answer

i)It may be base because bases change the colour of litmus paper to blue. As the color of blue litmus paper is not affected, the solution must be basic
ii) The solution may be neutral because solution not change the colour of the blue litmus paper.

Question 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, c and d

(iv) only d

Answer

Only d