NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts

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Updated at 2021-04-08


NCERT solutions for class 7 Science Chapter 5 Acids Bases Salts Exercise

Q.1 State differences between acids and bases.



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

ACID

(1) Acids are sour in taste.
(2) Acid turns blue litmus paper into the red.
(3) Acids do not change the color of the red litmus.
(4) Acids do not change the color of turmeric.
(5) With the china rose indicator, acids give dark pink color.
(6) Acid is a substance which contain H+

BASE

(1) Bases are bitter to taste.
(2) Base turns red litmus paper into the blue
(3) Bases dont change the color of blue litmus .
(4) Bases turn turmeric to red.
(5) With China rose indicator, bases give the green color.
(6) Base is a substance that contains OH?

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



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

Basic in nature.

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



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

1. Litmus solution is extracted from lichens.

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

3. It has a mauve (purple) color in distilled water. When added to an acidic solution, it turns red. When added to a basic solution, it turns blue.

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



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

Distilled water is neutral in nature.

We can verify it by showing that neither blue nor red litmus paper changes its color when dipped in it.

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



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

1. The reaction between an acid and a base is known as a neutralization reaction.

2. In this reaction, both acid and base cancel each other's effect.
Neutralization reaction results in the formation of salt and water.

3.During this reaction, energy in the form of heat is evolved.

For example:

When sodium hydroxide (NaOH) is added to hydrochloric acid (HCl), sodium chloride (NaCl) and water (H2O) are obtained and heat is evolved.

NaOH + HCl ? NaCl + H2O + Heat

Q.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)



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

(i) Nitric acid turns red litmus blue. (F)

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

(iii) Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T)

(iv) Indicator is a substance which shows different colours in acidic and basic solutions.(T)

(v) Tooth decay is caused by the presence of a base.(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?



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

1.

Dorji can use litmus paper to check if the drink is acidic, basic, or neutral and
can serve the correct drink as per the demand of the customers.

(i) If the drink turns red litmus to blue then that drink is basic in nature.

(ii) If the drink turns blue litmus to red then that drink is acidic in nature.

(iii) The drink which doesn't affect both red and blue litmus would be neutral.

2. Dorji can taste a few drops out of soft drinks bottles, the acidic solution is
sour in taste, the basic solution is bitter in taste, and the neutral solution has no taste.

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.



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

(a) Acidity is caused when an excess of acids is produced in the stomach.
The antacid tablet contains base-like milk of magnesia which neutralizes
the acid produced in the stomach, thus giving relief. Hence, it is used while suffering from acidity.

(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 to bring relief for the affected person.
Hence calamine neutralizes the effect of formic acid.

(c) Factory wastes contain acids. Therefore, these wastes, when thrown
directly to water bodies, harm aquatic lives. Hence, these wastes are
neutralized with basic chemicals before disposing to 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.



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

The following steps are taken to test the given liquids:

(1) Put a drop of provided liquid on the turmeric indicator. The solution that changes the color of the indicator to red, is sodium hydroxide, which is basic in nature.

(2) Now, to make two mixtures, add a drop of sodium hydroxide on the other two liquids individually. The drop of each combination added to the turmeric indicator one after another.

(3) The mixture that changes the indicator to red colour includes a neutral solution of sugar.

(4) While the mixture that does not show any color change in the indicator includes hydrochloric acid that has been neutralized by the addition of sodium hydroxide,

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



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

1. The solution is basic or neutral in nature.

2. We know acid turns blue litmus to red and neutral solution has no effect on the litmus paper.
As there is no change in color, so, the solution can be either basic or neutral.

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)



NCERT Solutions for Class 7 Science Chapter 5 Acids Bases Salts


Answer :

(iv) only (d)



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