In a gas jar containing hydrogen chloride gas, a dry blur litmus paper is dropped. What change is observed ? Now a blur litmus paper is moistened and dropped into the gas jar. State what is observed and give a reason for this.

Explanation

Dry blue litmus remains unchanged in colour in the gas jar containing hydrogen chloride gas but when blue litmus paper is moisoned, its colour changes to red. Actually, in the absence of moisture, hydrogen chloride gas does not release `H^(+)` ions and can not behave as an acid. But in the presence of moisture, the gas dissolves to from hydrochloride acid. It releases `H^(+)` ions and as a result, the colour of blue litmus changes to red.