Question

Why dry HCL do not change bule litmus to red litmus.

Answer 1

because there is no intermediate for the ions to dissociates so dry hcl will do not change blue litmus to red. Acids shows acidic properties only when dissolved in water and they produce hydronium ions.

Answer 2

Because it is not dissipated into h+ ions without the presence of water .
HCl + H2O ------> H3O(+) + H(+) + Cl(-)