NCERT Solutions for Class 7 Science Chapter 4 Acids, Bases and Salts

NCERT Solutions Class 7 Science Chapter 4 Acids, Bases and Salts are provided here to help students in understanding the topic thoroughly. All these solutions are solved by experts with a detailed explanation. Class 7 NCERT Solutions for Science Chapter 4 includes all the textbook exercise questions and answers. These solutions will help students complete their assignments & homework.

Class 7 Science Acids, Bases and Salts Questions and Answers

Exercise Questions

Question 1: State differences between acids and bases.


Acids are sour in tasteBases are bitter in taste
Acids turn blue litmus paper into red colourThe base does not change the colour of blue litmus paper
Acids do not change the colour of the red litmusBases turn red litmus paper to blue colour
Acids do not change the colour of turmeric indicator.Bases turn the colour of turmeric indicator to red.
Examples: Curd, lemon juice and vinegar.Examples: Baking soda, Soap and lime water.

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

Answer: Bases turn red litmus blue, so nature of ammonia is basic.

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. Litmus solution is used as an indicator to find acidic and basic nature of a solution.

Question 4: Is the distilled water acidic/basic/neutral? How would you verify it?

Answer: Distilled water is neutral by nature. We can verify it by litmus test. Water does not change the colour of either red or blue litmus.

Question 5: Describe the process of neutralisation with the help of an example.

Answer: 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.

Acid + Base → Salt + Water + Heat

For example, when sodium hydroxide (NaOH) is added to hydrochloric acid (HCl), sodium chloride (NaCl) and water (H2O) are obtained.

 NaOH + HCl → NaCl + H2O + Heat

Question 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)

(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 use litmus test on these drinks. Just drop few drops of drink on litmus paper and take the decision according to the following:

  • If it turns blue, drink is basic.
  • If it turns red, drink is acidic.
  • If it turns green, drink is 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.


(a) Due to the release of excess of hydrochloric acid, we suffer from acidity. An antacid tablet consists of a base like Milk of Magnesia (magnesium hydroxide). It neutralizes the effect of excessive acid and brings 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) The wastes of factories contain acids. If acids are disposed off in the water body, the acids may harm the aquatic organisms. Hence, these wastes are neutralised with basic chemicals before disposing to 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: Add solution to container with turmeric indicator. If the solution is NaOH, it would turn turmeric indicator to red. To the same container, add test solution number 2. If the added solution is sugar solution indicator remains red because mixture of basic and neutral solution will remain basic in nature.

Similarly, add the test solution number 3 to another container with turmeric indicator. If the indicator remains red then the solution will be hydrochloric acid.

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

Answer: If a blue litmus paper when dipped in a solution, remains blue, it implies the solution is either basic or neutral.

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) and (c)
(iv) only (d)

Answer: (ii) (a) and (d)

Having a good grasp over CBSE NCERT Solutions for Class 7 Science will further help the students in their preparation for board exams and other competitive exams. NCERT Solutions for Class 7 Science Chapter 4 Acids, Bases and Salts provided by CBSE Path help students to clear their doubts and to obtain good marks in the exams. All the solutions provided in this article are strictly based on the CBSE syllabus and curriculum.

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