Chapter 2, Problem 2.58P

Interpretation Introduction

Interpretation:

It is to be explained why hard water ions like ${\text{Ca}}^{\text{2+}}$ and ${\text{Mg}}^{\text{2+}}$ bind more strongly to carboxylate groups in soap than ${\text{Na}}^{\text{2+}}$ and ${\text{K}}^{+}$ ions.

Concept introduction:

Hard water contains a significant amount of ${\text{Ca}}^{\text{2+}}$ and ${\text{Mg}}^{\text{2+}}$ ions. These ions bind more strongly to the negative charge of carboxylate than ${\text{Na}}^{\text{2+}}$ and ${\text{K}}^{+}$ ions, causing the long-chain fatty acids to precipitate from water. Hard water does not form good lather with soap, hard water ions bond more strongly to the carboxylate group of soap to form insoluble scum resulting in a decrease in the cleaning property of hard water. Soft water ions form soluble lather with soap which are responsible for the cleaning property of soap in soft water.