Question

What will be the action of the following substances on litmus paper? Dry HCl gas, Moistened NH₃ gas, Lemon juice, Carbonated soft drink, Curd, Soap solution.

Answer 1

A type of paper that changes colour in reaction to the acidity of the solution it is dipped in, making it useful for measuring acidity.

1. Dry HCl gas has no effect on the paper because they are both devoid of water.
2. When wet, NH₃ gas turns red litmus blue because it forms Ammonium ion $\left({\mathrm{NH}}_4^{+}\right)$ and hydroxyl ion(OH⁻).
3. Lemon juice contains Citric acid$\left({\mathrm{C}}_6{\mathrm{H}}_8{\mathrm{O}}_7\right)$, which allows it to turn blue litmus red.
4. When a carbonated soft drink is consumed, blue litmus turns red because carbonated soft drinks contain carbonic acid that reacts with the litmus paper.
5. When the curd is added, the lactic acid present in the curd turns blue litmus red.
6. When soap is dissolved in water, alkaline NaOH or KOH is formed that change the red litmus to blue.