Question

(a) What is a universal indicator? For what purpose is it used?
(b) How does a universal indicator work?
(c) Water is a neutral substance. What colour will you get when you add a few drops of universal indicator to a test-tube containing water?

Answer 1

(a) A universal indicator is a combination of different dyes that show colour change with solutions of different pH values on the complete pH scale.
A universal indicator paper is used to differentiate between acids and bases. It also differentiates between strong acids and bases and between weak acids and bases on the basis of the intensity of colour change.

(b) When one or two drops of an acid or a base solution are added to a universal indicator paper, it generates a new colour. By comparing the colour with the pH scale, the pH of the added solution is known. From the pH value, we can identify the strength of the acid or base solution.

(c) A neutral substance has a pH value of 7. When we add a few drops of a universal indicator to a test tube of water (which is a neutral substance), we get a green colour, indicating the neutrality of water.