Question

why does dry HCL gas not change the colour of dry litmus paper

Answer 1

This is under normal conditions, not anhydrous conditions. Dry Hcl gas does not contain any hydrogen ions in it, so itdoes not show acidic behaviour. Dry HClgas does not change the colour of dry litmus paper as it has no hydrogen ions [H+(aq) ions] in it. ... And changes the color of litmus paper to RED.

Answer 2

Explanation: Colour of the litmus paper is changed by the hydrogen ions. Dry HCl gas does not contain H+ ions. It is only in the aqueous solution that an acid dissociates to give ions. Since in this case, neither HCl is in the aqueous form nor the litmus paper is wet, therefore, the colour of the litmus paper does not change.