Soaps consist of compounds such as sodium stearate, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{COO}^{-} \mathrm{Na}^{+},$ that have both hydrophobic and hydrophilic parts. Consider the hydrocarbon part of sodium stearate to be the "tail" and the charged part to be the "head." (a) Which part of sodium stearate, head or tail, is more likely to be solvated by water? (b) Grease is a complex mixture of (mostly) hydrophobic compounds. Which part of sodium stearate, head or tail, is most likely to bind to grease? (c) If you have large deposits of grease that you want to wash away with water, you can see that adding sodium stearate will help you produce an emulsion. What intermolecular interactions are responsible for this?

Step by step solution

01

Understanding Sodium Stearate Structure

Sodium stearate has a hydrocarbon part (tail) \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16}\) and a charged part (head) \(\mathrm{COO}^{-} \mathrm{Na}^{+}\). The tail is a long-chain hydrocarbon, which is hydrophobic (non-polar), while the head is ionic, consisting of a carboxylate group and a sodium ion, and it is hydrophilic (polar).

02

Solvation by water

(a) Solvation mainly depends on the compatibility of substances. Water is a polar solvent; thus, it solvates polar or hydrophilic parts of a compound. In the case of sodium stearate, its head (the charged part \(\mathrm{COO}^{-} \mathrm{Na}^{+}\)) is hydrophilic and more likely to be solvated by water.

03

Grease binding

(b) Grease, a complex mixture of hydrophobic compounds, will interact more with hydrophobic compounds or non-polar parts of a molecule. In sodium stearate, the tail (the hydrocarbon part \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16}\)) is hydrophobic and more likely to bind to grease.

04

Emulsion formation

(c) Introducing sodium stearate into a mixture of grease and water creates an emulsion, in which small droplets of grease are surrounded by sodium stearate molecules. The intermolecular interactions responsible for this process are: 1. Hydrogen bonding and ion-dipole interaction between the sodium stearate's head and water molecules. 2. London dispersion force between the sodium stearate's tail and grease molecules. These interactions result in the formation of an emulsion, thus allowing the removal of grease while washing with water.

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