Question

Dry HCl gas does not change the colour of dry litmus paper. Why?

Answer 1

Dry Hydrochloric acid ( HCl) gas is not acidic in nature and so it does not change the colour of dry litmus paper.

It is because only when dissolved in water, it gets dissociated into its respective ions( H+ and Cl- ions) and shows its acidic character.

Only then it changes the colour of blue litmus paper into red as hydronium ions are formed in water.

Answer 2

Explanation:

Litmus paper is defined as the indicator which is used to determine the nature of the solution. Whether it is acidic or basic.

There are 2 types of litmus paper:

• Red litmus paper: This paper will turn blue if it is dipped in basic solution and it remains as such if it is dipped in acidic solution.
• Blue litmus paper: This paper will turn red if it is dipped in acidic solution and remains as such if it is dipped in basic solution.

HCl is an acid and when it is dissolved in water, it dissociates into $H^+\text{ and }Cl^-$ ions

So, dry HCl gas does no react with dry litmus paper because, no solution is formed and HCl does not dissociates into its ions.

Hence, dry HCl gas does not change the color of dry litmus paper.