Question

(a) What is an indicator? Name three common indicators.
(b) Name the acid-base indicator extracted from lichen.
(c) What colour does the turmeric paper turn when put in an alkaline solution?

Answer 1

Hint:A substance will be known as an acid if it gives out hydrogen ions that is ${H^ + }$ ions when dissolved in water. A substance will be known as a base if it gives out hydroxide ions that is $O{H^ - }$ ions when dissolved in water. In order to find whether a solution is acidic or basic, indicators are used.

Complete answer:
(a) Indicator is a substance which changes its colour when it comes in contact with an acid or a base. An acidic substance is a substance which includes acid within itself. A basic substance is a substance which includes base within itself. An indicator is used to differentiate between an acidic substance and a basic substance. There is a range of different indicators. Among all, the common indicators are as follows; litmus, china rose, turmeric and phenolphthalein.
(b) The acid-base indicator which is extracted from lichen is litmus. Litmus can be used as a litmus solution or litmus paper.
(c) The colour of turmeric paper is yellow. When put in an alkaline or basic solution, the turmeric paper changes its colour to red. The turmeric paper does not change its colour when put in an acidic solution.

Note:
Indicators are subdivided into two types which are as follows; natural indicators and synthetic indicators. The examples of natural indicators are litmus, china rose and turmeric. The example of a synthetic indicator is phenolphthalein.