NCERT Solution class 7 Science Chapter-5

NCERT Solution class 7 Science Chapter-5

Chapter – 5 Acids, Bases and Salts

Chapter Exercise

Page No. – (56)

 

Q.1-  State differences between acids and bases.

Ans.1-

Acids Bases
Acids are sour in taste Bases are bitter in taste
Acids turn blue litmus paper into red colour Bases turn red litmus paper into blue colour
Acids does not change red litmus paper Bases does not change blue litmus paper

 

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

Ans.2- Ammonia has basic nature.

 

Q.3- Name the source from which litmus solution is obtained.

What is the use of this solution?

Ans.4- Litmus solution is extracted from lichens. It is used as an indicator to find is acidic or basic.

 

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

Ans.4- Distilled water is neutral in nature. We can verify it by showing that neither blue nor red litmus paper changes its colour when dipped in it.

 

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

Ans.5- The reaction between an acid and a base are known as neutralization. Salts and water are produced in this process with evolution of heat.

HCL + NaOH_NaCl + H2O.

 

Q.6- Mark ‘T’ if the statement is true and ‘F’ if it is false:-

  1. Nitric acid turns red litmus blue. (T/F)
  2. Sodium hydroxide turns blue litmus red. (T/F)
  3. Sodium hydroxide and hydrochloric acid neutralise each other and form salt and water. (T/F)
  4. Indicator is a substance which shows different colours in acidic and basic solutions. (T/F)
  5. Tooth decay is caused by the presence of a base. (T/F)

Ans.6-

i. F

ii. F

iii. T

iv . T

v. 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?

Ans.7- Dorji can decide with the help of indicator (litmus Paper).

Sample 1:- if turn blue litmus paper into red, so it is Acidic.

Sample 2:- if turn red litmus paper into red, so it is Basic.

Sample 3:- if litmus does not effect, so it is Neutral.

 

Q.8- Explain why:-

  1. An antacid tablet is taken when you suffer from acidity.
  2. Calamine solution is applied on the skin when an ant bites.
  3. Factory waste is neutralised before disposing it into the water bodies.

Ans.8- a) We take an antacid such as milk of magnesia to neutralises the excessive acid released in stomach.

  1. B) When an ant bites, it inject formic acid in skin. Calamine solution contain zinc carbonate which is a basic in nature. Therefore, it is applied on skin to neutralize the effect of formic acid.
  2. c) Factory wastes are acidic or much in nature which may cause harm to the aquatic life. So, they are neutralised by using a base 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.9- Turmeric Solution turn red in contact with bases. Also It is not affected by the acids and natural substances.

First we will identify the Base.

Turmeric add in base, it will turn red. Then, next another solution added slowly. If the solution turn in yellow colour so, added colour is Hydrochloric. If not, so added liquid is Sugar solution.

 

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

Ans.10- Bases or Neutral in Nature. Because both type can’t affect on blue litmus Paper.

 

Q.11- Consider the following statements:-

  1. Both acids and bases change colour of all indicators.
  2. If an indicator gives a colour change with an acid, it does not give a change with a base.
  3. If an indicator changes colour with a base, it does not change colour with an acid.
  4. Change of colour in an acid and a base depends on the type of the indicator. Which of these statements are correct?
  5. All four
  6. a and b
  • b, c and d
  1. Only d.

Ans.11- iv. Only d.

 

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