CLASS 7 Chapter 5 Acids, Bases and Salts

Question1 State the difference between acids and bases

Solution1

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

Solution 2. ammonia that is found in many household products and turns red litmus blue has basic nature.

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

Solution 3. litmus is a natural indicator which is extracted from lichens. Litmus solution is used to determine whether the given solution is acidic or basic.

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

Solution 4. Distilled water is neutral. We would verify that distilled water is neutral by showing that when we dip red or blue litmus paper neither of them changes its colour.

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

Solution 5.  When an acid reacts with a base this process is called neutralisation. Salt and water are produced in the process of neutralisation with the evolution of heat.

To reduce acidity in the stomach when excessive acid is released by glands, we use antacids like milk of magnesia, baking soda, etc. which is basic in nature.

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 neutralize and form salt and water. (T/F)
(id) The 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)

Solution 6. (i) Nitric acid turns red litmus blue. False
(ii) Sodium hydroxide turns blue litmus red. False
(iii) Sodium hydroxide and hydrochloric acid neutralize and form salt and water. The true
(id) Indicator is a substance which shows different colours in acidic and basic solutions. True
(v) Tooth decay is caused by the presence of a base. False

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

Solution 7. Dorji can decide which drink is to be served to whom by using a litmus paper

1. The drink which turns the red litmus paper into blue in colour would be a basic drink.
2. The drink which turns the blue litmus paper red in colour would be an acidic drink
3. The drink which does not affect any of the litmus paper 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 neutralized before disposing it into the water bodies.

Solution 8. a) We take antacids to neutralize the excessive acid released in the stomach.

1. b) Ant injects an acidic liquid into the skin on biting which causes inflammation to the skin to neutralize the acidic liquid in the skin calamine solution is used which contains zinc carbonate which is a very weak base and causes no harm to the skin.
2. c) the wastes from the factory contain acid which harms the organisms if disposed of in the water. So factory waste is neutralized by adding essential substances before disposing of it.

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

Solution 9.  Note the effect of these substances on turmeric

1. Hydrochloric acid turns yellow into blue.
2. Sodium hydroxide turns yellow into

• Sugar solution does no effect.

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

Solution 10. If a blue litmus paper is dipped in a solution and it remains blue then the solution is neutral.

Question 11. Consider the following statements:
(a) Both acids and bases change the 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)

Solution 11. ii) (a) and (d)