Question

A student tested the pH of distilled water and found that the colour of pH paper changed to green. He checked the pH again after dissolving a pinch of common salt in water. The colour of pH paper this time was:
A.Green
B.Yellow
C.Red
D.Blue

Answer 1

Hint: Distilled water is one type of purified water. Its impurities are removed by boiling normal water. Litmus paper is a \[pH\]paper/filter paper. It is a very easily understood and popular \[pH\]indicator. It is used to test whether a solution is acidic or basic. It indicates red colour when \[pH\]is below 4.5, green colour when the solution is neutral and blue colour when \[pH\] is above 8.5. The \[pH\] scale varies from 0 to 14.

Complete step by step answer:
The student tested the pH of distilled water. Since distilled water is neither acidic nor basic, the colour of the \[pH\]paper changed to green indicating that it is neutral in nature.
The\[pH\]of the distilled water is around 7.
When a pinch of common salt is added in water, the colour of the \[pH\]paper does not change. This is because common salt is a combination of strong acid-strong base that is a combination of hydrochloric acid (HCl) – sodium hydroxide (NaOH).
So, the colour of the \[pH\]paper was green.
So, the correct option is A.

Note:
If a red litmus paper is dipped into the distilled water, it remains red and if a blue litmus paper is dipped into the distilled water, it remains blue. If a red litmus paper is dipped into an acidic solution, it remains red. If a blue litmus paper is dipped into a basic solution, it remains blue.