Chapter 2, Problem 2.29P

Interpretation Introduction

Interpretation:

Whether the given hypothetical compound can act as soap is to be determined.

Concept introduction:

Soaps are sodium or potassium salts of fatty acids. They are ionic molecules that contain a hydrophilic group at one end and a hydrophobic group at the other end of the molecule. The hydrophobic end is typically a hydrocarbon group with a 12 to 18 carbon chain. It interacts with nonpolar substances like dirt, grease, and oil, bonding strongly because they are also nonpolar. The hydrophilic end is the carboxylate ion, a polar group that forms strong dipole-dipole interactions as well as hydrogen bonds with water.

An oil droplet for example, will dissolve the hydrophobic tail of the fatty acid anions, and be surrounded by them. The polar carboxylate groups of the soap molecules will be on the outside of this droplet and will interact strongly with water molecules, forming an emulsion, which can then be washed off by excess water.