Question

(a) Would you expect stearic acid, \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{COOH}\), to be more soluble in water or in carbon tetrachloride? Explain. (b) Which would you expect to be more soluble in water, cyclohexane or dioxane? Explain.

Short answer

(a) Stearic acid would be more soluble in carbon tetrachloride because it has a long nonpolar hydrocarbon tail that is better suited to dissolve in nonpolar solvents. (b) Dioxane, a polar compound, would be more soluble in water, a polar solvent, than nonpolar cyclohexane.

Step-by-step solution

Understand the principle of "like dissolves like"

The principle "like dissolves like" states that polar substances tend to dissolve in polar solvents, while nonpolar substances tend to dissolve in nonpolar solvents. This is because solute-solvent interactions should replace solute-solute or solvent-solvent interactions without losing too much energy. Now, use this principle to answer both parts of the exercise.

(a) Determine the polarity of stearic acid, water, and carbon tetrachloride.

Stearic acid has a polar carboxylic acid group (COOH) and a nonpolar hydrocarbon tail. Water is a highly polar solvent due to its hydrogen bonding capability. Carbon tetrachloride is a nonpolar solvent, having no net dipole moment.

(a) Compare the solubility of stearic acid in water and carbon tetrachloride.

Since stearic acid has a long nonpolar hydrocarbon tail, it would be more soluble in the nonpolar solvent, carbon tetrachloride. The polar carboxylic acid group does not dominate stearic acid's polarity due to the length of the nonpolar tail. Therefore, stearic acid would be more soluble in carbon tetrachloride than in water.

(b) Determine the polarity of cyclohexane and dioxane.

Cyclohexane is a nonpolar compound, as it consists of only carbon and hydrogen atoms in a ring structure. Dioxane, on the other hand, has oxygen atoms and has polar C-O bonds, making it a polar compound.

(b) Compare the solubility of cyclohexane and dioxane in water.

Following the principle of "like dissolves like," the polar compound dioxane would be more soluble in water, as water is a polar solvent. Cyclohexane, being nonpolar, would be less soluble in water.