Question

Explain why methyl alcohol is soluble in water in all proportions, while stearyl alcohol \(\left[\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16} \mathrm{OH}\right]\) is a waxy solid that is not soluble in water.

Short answer

Methyl alcohol is soluble in water in all proportions because both are polar molecules and can form strong hydrogen bonds. On the other hand, stearyl alcohol is insoluble in water due to its long nonpolar hydrocarbon chain which dominates the molecule, making it primarily hydrophobic. While the small polar hydroxyl group in stearyl alcohol can form hydrogen bonds with water, the unfavorable interactions between the hydrocarbon chain and water prevail, resulting in its insolubility in water.

Step-by-step solution

Analyze the structure of methyl alcohol and water.

Methyl alcohol, or methanol, has a molecular formula of \(\mathrm{CH}_{3}\mathrm{OH}\). Water has a molecular formula of \(\mathrm{H}_{2}\mathrm{O}\). Both molecules are polar, due to the electronegativity difference between oxygen and hydrogen or carbon atoms. The presence of oxygen in both molecules creates an effective dipole (separation of positive and negative charges).

Explain the interactions between methyl alcohol and water molecules.

Since both methyl alcohol and water are polar molecules, they form strong hydrogen bonds between the hydroxyl groups (\(\mathrm{-OH}\)) of their respective molecules. The hydrogen bond is a strong intermolecular force that helps to facilitate the dissolution of polar compounds in water. As a result, methyl alcohol is soluble in water in all proportions.

Analyze the structure of stearyl alcohol.

Stearyl alcohol has the molecular formula \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{16}\mathrm{OH}\). The molecule consists of a long hydrocarbon chain with one hydroxyl group at the end. The long hydrocarbon chain is nonpolar due to the similar electronegativity values of the carbon and hydrogen atoms. While the hydroxyl group is polar, the majority of the molecule is dominated by the nonpolar characteristics of the hydrocarbon chain.

Explain the interactions between stearyl alcohol and water molecules.

Since stearyl alcohol molecule consists of a large nonpolar hydrocarbon chain and only a small polar hydroxyl group, it is primarily hydrophobic. This hydrophobicity means that the nonpolar part of stearyl alcohol does not interact favorably with polar water molecules. While the hydroxyl group can still form hydrogen bonds with water, the unfavorable interactions between the hydrocarbon chain and water dominate, making stearyl alcohol insoluble in water.

Summarize the findings from the analysis.

In summary, methyl alcohol is soluble in water because it is a polar compound that can form hydrogen bonds with water molecules. In contrast, stearyl alcohol is a waxy solid that is insoluble in water due to the hydrophobic nature of its long hydrocarbon chain, which dominates over the ability of its hydroxyl group to hydrogen bond with water.