NCERT Solutions for Class 7th Science

Chapter 5 – ACIDS, BASES AND SALTS

(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)

 

Q.1      State differences between acids and bases.

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

Ans     Since ammonia turns red litmus blue, it is basic in nature.

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

Ans     Litmus is extracted from lichens. It has a mauve (purple) colour in distilled water. It is used to detect                    acidic or basic solution. When added to an acidic solution, it turns red and when added to a basic                          solution, it turns blue.

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

Ans     Distilled water is neutral in nature. It can be verified by using litmus paper. Distilled water neither                         changes colour of blue litmus paper to red nor red litmus paper to blue.

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

Q.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)

Ans     (i) Nitric acid turn red litmus blue. (F)

           (ii) Sodium hydroxide turns blue litmus red. (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?

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.

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.

Ans      1. Take all the liquids in different beakers or test tubes.

            2. We will put drops of all the liquids on the turmeric indicator. The liquid which shows colour change of             turmeric indicator to red is the basic solution i.e. sodium hydroxide whereas the acidic and neutral                       solution will not show any colour change.

            3. Now we will mix basic liquid i.e. sodium hydroxide with the other two liquids in two different beakers.

            4. The beaker which becomes hot due to neutralization reaction is the one with the mixture of basic and               acidic liquid i.e. hydrochloric acid whereas the second one is with basic and neutral solution i.e. sugar                 solution.

            5. In this way all the three are identified.

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

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