What is an indicator? Give two examples along with their action in acids and bases.

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Solution

An indicator is a substance that changes it colour, depending on whether it is added to an acid or a base.
Examples of indicators are:

Litmus paper: Blue litmus paper turns red in the presence of an acid, while red litmus turns blue in the presence of a base.

Turmeric: It is a natural indicator that turns yellow in the presence of an acid and red in the presence of a base.

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Q. What is an acid-base indicator? Give one example.

Olfactory indicators with examples and their changes when react with acid or base

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?

Q. (a) Define an acid and a base. Give two examples of each.
(b) Give the names and formulae of two strong bases and two weak bases.
(c) What type of ions are formed:
(i) when an acid is dissolved in water?
(ii) when a base (or alkali) is dissolved in water?
(d) Write the neutralisation reaction between acids and bases in terms of the ions involved.
(e) Write any two important uses of bases.

Q. Match the following indicator types with their colour in acids/bases.

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