Class 7 Science NCERT Solutions for Chapter – 5 Acids, Bases and Salts

Acids, Bases and Salts

Question 1.
State differences between acids and bases.

Solution:

S. NoAcidsBases
(i)Acids are sour to taste.Bases are bitter to taste.
(ii)Acid turns blue litmus to red.Base turns red litmus to blue.
(iii)Acid is a substance which containsBases are substances which contain
(iv)hydrogen ion (H+).hydroxyl ion (OH)

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

Solution:
Basic.

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

Solution:
Lichens. It is used as indicator.

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

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

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

Solution:
The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
Acid + Base → Salt + Water
Heat is also evolved in this process.
The following reaction is an ,
example :
NCERT Solutions for Class 7 Science Chapter 5 Acids, Bases and Salts image 1

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)

Solution:
(i) F
(ii) F
(iii) T
(iv) T
(v) F

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 Doiji decide which drink is to be served to whom?

Solution:
He can decide by the use of indicator. If the sample of drink turns red litmus blue, it is basic. If it turns blue litmus red, it is acidic. If it does not effect litmus, it 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 where an ant bites.
(c) Factory waste is neutralised before disposing it into the water bodies.

Solution:
(a) Antacids are nothing but bases. When there is excess of acid in stomach, antacid are taken. Antacids neutralise acids and relieves us.
(b) Ant injects an acidic liquid into the skin during bite which causes the burning sensation. Calamine solution is basic in nature. It neutralises the acid and relieves us from the pain.
(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 off 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.

Solution:
Following steps are taken to test the given liquids :
(a) Place a drop of each liquid on turmeric indicator. The solution which changes the colour of the indicator to red is basic in nature, i.e., it is sodium hydroxide.
(b) Now put a drop of sodium hydroxide on the other two liquids separately to obtain two mixtures.
(c) One by one place the drop of each mixture on turmeric indicator. The mixture that changes the colour of indicator red contains neutral sugar solution. While the mixture which does not show any colour change in indicator contains hydrochloric acid which was neutralised on addition of sodium hydroxide.

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

Solution:
The solution may be neutral or basic. Both types of substance have no effect on blue litmus. Put a drop of this solution on a red litmus paper. If it turns blue, then the above solution is basic in nature and if no colour change occurs, then it is 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)

Solution:
(iv) only (d).

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