Question

Sudha took a small amount of sulphur in a deflagrating spoon and heated it over a burner. As soon as it started burning she put it in a gas jar and covered it with a lid. After sulphur stopped working she added a small amount of water in it and dissolved the gas in water by shaking it. She then tested the solution with red and blue litmus paper and what she observed.
(A) In the solution, the blue litmus paper turns red.
(B) In the solution, the red litmus paper turns blue.
(C) There was no change in color of litmus paper.
(D) Blue litmus paper turns red and red litmus paper turns blue.

Answer 1

Hint:Sulphur burns in presence of oxygen to give a colorless toxic gas which on further reaction with water gets converted into a dibasic acid and yields hydrogen ions. When you dip a litmus paper it changes its colour.


Complete solution:
The atomic number of Sulphur is $16$. It is non-metal. It is abundant, odorless, and tasteless. It exists in nature as yellow crystals. It reacts with all the metals except Gold and Platinum. When sulphur is burned, it reacts with oxygen to form sulphur dioxide ($S{O_2}$) gas.
$S + {O_2}(g) \to S{O_2}(g)$
 Sulfur dioxide is a colorless gas with a rotten egg smell. It is a toxic gas and a major air pollutant, hence it is very toxic to human beings. It can be used as an oxidizing agent as well as a reducing agent. When you add water to sulfur dioxide gas, It reacts with ${H_2}O$ and gets converted into sulfurous acid. In the presence of water, Sulfur dioxide works as a bleaching agent and makes the solution acidic.
$S{O_2} + {H_2}O \to {H_2}S{O_3}$
Since the solution is acidic so when you put blue litmus paper in it. It will turn blue litmus red. This is the observation that will be observed by Sudha when she put blue litmus in the solution.

Thus, the correct option is (A) .


Note:Sulfurous acid is a weak dibasic acid and a strong reducing agent. It is also a part of acid rain, so it reacts with oxygen present in the atmosphere to get converted into Sulphuric acid. Both of these acids are very harmful to living beings.