Question

Dry hydrogen chloride gas does not affect a dry strip of blue litmus paper but it turns red in the presence of a drop of water why?

Answer 1

Answer:

Any acid is said to be an acid if there is a proton acceptor. Since, water is a proton acceptor and form hydronium ion or in another words, acid molecules are ionized and release protons.

Dry strip of litmus and dry HCl do not contain any water, so do not get ionize, but in the presence of a drop of water, HCl is ionized and release proton, that turns blue litmus to red.

It so happens because any two or more element reacts with each other only in presence of hydrogen ions . Thus a dry litmus paper will not show any effect in the presence of dry HCL due to the absence of moisture(H+ ions) in the the litmus paper , whereas on putting a drop of water,the blue litmus paper immediately turns to red due to the presence of water in it hence presence of hydrogen ions(H+ ions).