WAEC Chemistry 2022 Paper

Concept:Soap is a salt of a long-chain fatty acid, and it loses its cleansing power in acidic water because the acid converts it to the fatty acid.Explanation:Soap molecules are typically sodium or potassium salts of long-chain fatty acids, such as $\mathrm{RCOO^-Na^+}$.In acidic water, the $\mathrm{H^+}$ ions from the acid react with the soap anion $\mathrm{RCOO^-}$.This reaction produces an unionized, insoluble long-chain fatty acid, $\mathrm{RCOOH}$.The insoluble fatty acid precipitates out of the solution, preventing lather and foam formation.Therefore, the cleansing effect is reduced because the soap is no longer available as soluble ions.Answer:A. the formation of unionized fatty acid.