Why does dry hcl gas not change the colour of the dry litmus paper

General
1

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

2

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

Answer:
Dry hydrogen chloride (HCl) gas does not change the colour of dry litmus paper because it does not exhibit acidic properties in the absence of water. Here’s a detailed explanation:

Solution By Steps:

  1. Nature of HCl gas:

    • Hydrogen chloride (HCl) is a diatomic molecule consisting of hydrogen and chlorine atoms. In its gaseous state, HCl exists as simple molecules without dissociation into ions.

  2. Role of Water in Acidic Behavior:

    • The characteristic acidic behavior of HCl is observed only when it is dissolved in water. In aqueous solution, HCl dissociates completely to form hydrogen ions (H⁺) and chloride ions (Cl⁻).

      \text{HCl} (g) \rightarrow \text{HCl} (aq) \rightarrow \text{H}^+ (aq) + \text{Cl}^- (aq)

    • The presence of hydrogen ions (H⁺) or hydronium ions (\text{H}_3\text{O}^+) in water is what gives acidic properties to substances and leads to the change in colour of pH indicators like litmus paper.

  3. Dry Litmus Paper:

    • The litmus paper contains litmus, a dye that changes colour in the presence of an acid (turning red) or a base (turning blue). However, for the litmus paper to show a colour change, the acidic or basic substance needs to be in a solution where ions are present.

  4. Interaction Between Dry HCl Gas and Dry Litmus Paper:

    • When HCl gas is dry and the litmus paper is also dry, there is no medium (water) for the HCl to ionize.
    • Therefore, dry HCl gas cannot produce hydrogen ions (\text{H}^+) and thus cannot exhibit its acidic properties. Consequently, the dry litmus paper remains unchanged in colour.

Conclusion:

In summary, dry HCl gas does not change the colour of dry litmus paper because the gas does not dissociate into hydrogen ions without the presence of water. The absence of water means there is no formation of \text{H}^+ ions, which are responsible for the acidic behavior that changes the colour of litmus paper. Thus, both the HCl gas and the litmus paper need to be in the presence of water for the colour change to occur.