Question

What happens to the colour of litmus paper when you put a drop of an acid on it?
A. it gets destroyed
B. from red it turns blue
C. from blue it turns red
D. it is unaffected by acid

Answer 1

Hint: As we know that litmus paper is used to test the pH balance of a substance or liquid. Most of the substances are either acid or alkali. It is found that blue litmus is used to test acidic pH level and red litmus is used to test acidic pH level

Complete answer:
- As we know that the main use of litmus is to test whether a solution is acidic or basic.
- PH of a substance is the measure of its acidic or alkaline medium, that has the range from 1-14 pH.
- Acidic medium have a range of pH about less than 7, and basic medium is found to have pH range higher than 7.
- When we put a drop of acid on blue litmus paper then it turns red. Whereas, we put a drop of acid on red litmus paper then it remains red.
- Under basic or alkaline conditions red litmus paper turns blue, with colour change occurring over the pH range of 4.5-8.3.

Hence, we can conclude that the correct option is (c), that is from blue it turns red.

Additional information:
- We have seen that blue and red litmus paper can detect the acidic or basic nature of the other substances by change in its colour. Hence, we can call it an acid-base indicator.
- We should not taste any substance in the laboratory soluble because it can be harmful. Hence, we can say that these are economically very much important to check whether a given substance is acid or a base.

Note:
- We must always remember that pH of 7 is neutral, a pH greater than 7 is basic and less than 7 is acidic.
- Blue litmus turns red in acidic medium, but remains unchanged in basic or neutral medium. Whereas, Red litmus turns blue in basic medium, but remains unchanged in acidic or neutral medium.