Solubility of khp in water is greater than many fatty acids because khp is a polar substance while fatty acids are non-polar. Khp has positive and negative charges which help it to dissociate into ions when it dissolves in water. Fatty acids on the other hand contain long unbranched hydrocarbons with one end having a carboxylic acid group. This make water molecules to repel from them because no part of the fatty acid molecules have any charge.
