Question

If you keep a blue litmus paper in hcl gas it does not change colour.while hcl acid turns blue litmus red what is the reason for this anomaly

Answer 1

The colour of litmus paper changes only in the presence of ions like hydrogen (H+) or hydronium (H3O+) ions. HCl can produce these ions only in the form of aqueous solution. Hence dry HCl gas does not change the colour of dry litmus paper.