Acids, Base and Salts Class 7 Worksheet Science Chapter 2

Q.1. Q.1. True/False
(i) Nitric acid turns red litmus blue.

False

(ii) Sodium hydroxide turns blue litmus red.

False

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

True

(iv) 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

(vi) If an indicator changes colour with a base, it does not change colour with an acid.

False

Q.2. Fill in the blanks.
(i) Change of colour in an acid and a base depends on the type of the ____.

indicator

(ii) Acid turns ____ litmus red.

blue

(iii) Bases turn ___ litmus blue.

red

(iv) Litmus has a ____ colour in distilled water.

mauve (purple)

(v) In neutralisation reaction a new substance is formed. This is called ____.

salt

(vi)  Lemon juice is ____ in nature.

acidic

Q.3. Why curd, lemon juice, orange juice and vinegar taste sour?

These substances taste sour because they contain acids.

Q.4. Tom rubs a solution between fingers and feels soapy, what is the nature of that solution?

Basic

Q.5. What do you mean by neutral solution? Give examples.

The solutions which do not change the colour of either red or blue litmus are known as neutral solutions. Examples- sugar solution, distilled water, etc.

Q.6. How does rain become acidic?

The rain becomes acidic because carbon dioxide, sulphur dioxide and nitrogen dioxide (which are released into the air as pollutants) dissolve in rain drops to form carbonic acid, sulphuric acid and nitric acid respectively.

Q.7. State few properties of acids.

Properties of acids

• Acids are sour in taste
• Acid turns blue litmus red.
• China rose indicator turns acidic solutions to dark pink (magenta).
• Turmeric indicator does not change its colour with acid
• Gives burning sensation.
• Acids are usually sticky.
• When the solution is acidic, phenolphthalein remains colourless.

Q.8. Which acid is present in an ant sting?

Formic acid is present in an ant sting.

Q.9. What is the nature of distilled water?

The Distilled water is neutral.

Q.10. Where does the word acid come from?

The word acid comes from the Latin word acere which means sour.

Q.11. Which is the most commonly used natural indicator?

The most commonly used natural indicator is litmus.

Q.12. Name the acid which is present in each cell of our body.

Each cell in our body contains an acid, the deoxyribonucleic acid or DNA.

Q.13. Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.

The solution could be a base or neutral solution because blue litmus paper doesn’t change its colour in the neutral as well as in basic solution.

Q.14. Is the distilled water acidic/basic/neutral? How would you verify it?

Distilled water is neutral in nature. This can be verified by using red and blue litmus papers. Neither will show change in colour with distilled water. This proves that distilled water is neutral.

Q.15. Why factory waste is neutralised before disposing it into the water bodies?

The wastes of many factories contain acids. If they are allowed to flow into the water bodies, the acids will kill fish and other organisms. The factory wastes are, therefore, neutralised by adding basic substances.

Q.16. What is acid rain?

The rain containing excess of acids is called an acid rain.

Q.17. What is the role of hydrochloric acid in the stomach?

Hydrochloric acid (HCl) helps us to digest food.

Q.18. Hydrochloric acid (HCl) helps us to digest food.

Acids - Curd, lemon juice, vinegar, orange juice etc.
Base - baking soda, lime water etc

Q.19. What is the effect of the China rose indicator on acidic and basic solutions?

China rose indicator turns acidic solutions to dark pink (magenta) and basic solutions to green.

Q.20. Why a turmeric stain on my white shirt is turned to red when it is washed with soap.

A turmeric stain on my white shirt is turned to red when it is washed with soap because the soap solution is basic in nature.