ACIDS , BASES AND SALTS COMPLETE QUESTION ANSWERS

IV. 1. What is an acid?

Ans: Acid is a compound that contains hydrogen , dissolves in water , sour in taste and corrosive in nature.

2. Name two food items that contains weak acids.

Ans: Lemons and curd

3. What is a base ?

Ans: Base is a compound that reacts with an acid and produces salt and water .

4. Name any two bases.

Ans: Sodium hydroxide and Ammonia

5. What happens when an acid reacts with a base ?

Ans: Salt is produced when an acid reacts with a base .

6. What is an alkali?

Ans: A base that readily dissolves in water is known as alkali.

Eg: Washing soda.

7. Why should a bee sting be treated with a base?

Ans: Bee sting contains formic acid and in order to neutralise it a base is used.

V. 1. What are indicators? Give two examples of natural indicators.

Ans: Indicators are those which are used to test if a given substance is an acid or a base.

Two examples of natural indicators are – Turmeric powder and Red cabbage extract .

2. What is meant by neutralisation of an acid by a base?

Ans: Neutralisation of an acid by a base means that the acid loses its acidity and the base its alkalinity.

3. How do toothpaste protect your teeth?

Ans: Bacteria present in the mouth feed on sugar particles and produces weak acids which damages teeth and gums . To prevent these damages toothpaste are used as they contain an alkali which neutralises the acid produced by the bacteria.

4. What are salts?

Ans: These are compounds formed when an acid and a base react.

Some naturally occurring salts are – Sodium chloride and Magnesium sulphate.Also some salts are soluble in water and some are not.

5. Why is rain water slightly acidic?

Ans: Rain water is slightly acidic because carbon dioxide from the air dissolves in water and forms mild carbonic acid , a weak acid.

VIII. 1. Write short note on different types of acid base indicators.

Ans: Indicators are those substances which changes colour when placed in acidic or basic conditions.

Acid – base indicators are dyes found in natural matter , whose acidic form has one colour and basic form has another colour. Eg: Colourless extract of bryophyllum leaves produces pink colour with an acid an yellow colour with a base.

Litmus is another acid – base indicator used in laboratories which is a natural dye obtained from lichens. This dye has two forms – red and blue . Acids turn blue litmus red and bases turn red litmus blue.

Other commonly used acid- base indicators are Methyl orange , Phenolphthalein .

2. How is the process of neutralisation helpful in agriculture?

Ans: Neutralisation plays an important role in agriculture.

Most plants grow well in natural soil , so if soil is more or too alkaline it will lessen the production of plants. If the soil is acidic , it is treated with bases like quicklime or slaked lime . Similarly if the soil is basic it is treated with organic manure which releases acids and neutralises the basic nature of soil.

3. Name any two useful salts and mention their uses.

Ans: Salts are compounds formed when an acid reacts with a base.

Two useful salts and their uses are –