Answer to Question #248678 in Physical Chemistry for Abhishek

Question

How did you account for the abnormally high mobility of OH- ions in water?

Answer 1

The hydrogen ion, because of its small size and therefore, high charge density, is heavily hydrated. Experimental evidence suggest that H+ ion in aqueous solution is hydrated to form H9O4+ ion that's a trihydrate H3O+.3H2O.

This structure because of the large size and shape, should predict the mobility of H+ ion to be lower. The high mobility of H+ ions in hydroxylic solvents such as H2O can be explained by Grothus mechanism in which a proton moves rapidly from H3O+ to a hydrogen bonded water molecule and is transferred further along a series of hydrogen bonded water molecules. This accounts for the high mobility of H+ ions in water.