Problem 30 - Chemistry: The Central Science

Question

Would you expect alanine (an amino acid) to be more soluble in water or in hexane? Explain.

Step-by-Step Solution

Answer

Alanine is expected to be more soluble in water due to its polar nature, which is caused by the presence of polar amino (-NH2) and carboxyl (-COOH) groups in its structure. The polar nature of alanine makes it more compatible with the polar solvent water, adhering to the "like dissolves like" rule. Hexane, a nonpolar solvent, is less likely to dissolve alanine effectively.

Step 1: Analyze the structure of alanine

First, let us analyze the structure of alanine. Alanine is an α-amino acid with the chemical formula CH3CH(NH2)COOH. It has an amino group (-NH2) and a carboxyl group (-COOH) on the same carbon atom. Due to the presence of these polar groups, alanine exhibits some polar characteristics.

Step 2: Analyze the structure of the solvents (water and hexane)

Now we have to analyze the structure of the solvents water and hexane: 1. Water (H2O) is a polar molecule due to the electronegativity difference between oxygen and hydrogen atoms. The presence of polar OH bonds gives water a high polarity and its well-known ability to dissolve various substances. 2. Hexane (C6H14) is a nonpolar molecule with single bonds between carbon and hydrogen atoms. No significant electronegativity difference exists between these atoms, resulting in a nonpolar molecule. Nonpolar molecules typically dissolve nonpolar substances.

Step 3: Comparing the solubility of alanine in water and hexane

Now that we have analyzed the structures of alanine, water, and hexane, we can compare alanine's solubility in these solvents. - Alanine contains both polar groups (-NH2, -COOH), which makes it partially polar. - Water is a polar solvent, and hexane is a nonpolar solvent. Recalling the rule "like dissolves like", we would expect alanine to be more soluble in a polar solvent, like water, than in a nonpolar solvent, like hexane. Therefore, we can conclude that alanine should be more soluble in water than in hexane.