Question

2) Desribe the effect of HCl (pH 4) in both a soap and a detergent solution. Include a chemical equation if a change occurred in either of the solutions.

Answer 1

Soap, in acidic media or acidic water loses its affinity towards cleaning action as it is reacting with salts of fatty acids present in soap.

Bath soaps contain sodium or potassium salts of fatty acids having -COOH group in it, where as detergents contain sodium or potassium salts of sulphonates or sulphates.

CH₃(CH₂)₁₄-COO⁻ K⁺ or CH₃(CH₂)₁₄-COO⁻ Na⁺ are present in bath soaps.

Detergents contain CH₃(CH₂)₁₂-OS(O)₂-O⁻ Na⁺

These salts when reacts with acid water, they become corresponding carboxylic acids or sulphates. Hence, they lose their affinity of cleaning action.

The reaction is as follows: C₁₇H₃₅COONa + HCl C₁₇H₃₅COOH + NaCl