In the following pairs of compounds, which would you expect to be more soluble in water? Why?
a. C₈H₁₇COOH or CH₃CH₂CH₂COOH

Verified step by step guidance

Step 1: Understand the solubility principle. Solubility in water is influenced by the ability of a compound to form hydrogen bonds with water molecules. Compounds with polar functional groups (e.g., -OH, -COOH) are generally more soluble in water than nonpolar compounds.

Step 2: Analyze the functional group in both compounds. Both compounds contain the carboxylic acid group (-COOH), which is polar and capable of forming hydrogen bonds with water. This functional group contributes to water solubility.

Step 3: Consider the hydrocarbon chain length. The solubility of a compound in water decreases as the length of its nonpolar hydrocarbon chain increases. This is because the nonpolar portion of the molecule resists interaction with water.

Step 4: Compare the two compounds. C₈H₁₇COOH has a longer hydrocarbon chain (8 carbons) compared to CH₃CH₂CH₂COOH (3 carbons). The longer chain in C₈H₁₇COOH makes it more hydrophobic, reducing its overall solubility in water.

Step 5: Conclude which compound is more soluble. CH₃CH₂CH₂COOH, with its shorter hydrocarbon chain, is expected to be more soluble in water than C₈H₁₇COOH because it has a smaller nonpolar region and can interact more effectively with water molecules.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hydrophilicity vs. Hydrophobicity

Hydrophilicity refers to the affinity of a substance to interact with water, while hydrophobicity indicates a lack of such affinity. Compounds with polar functional groups, like carboxylic acids, tend to be more hydrophilic due to their ability to form hydrogen bonds with water. In contrast, long hydrocarbon chains are hydrophobic, which can reduce overall solubility in water.

Carboxylic Acids and Solubility

Carboxylic acids, characterized by the presence of the -COOH group, are generally more soluble in water than their hydrocarbon counterparts. The polar -COOH group can engage in hydrogen bonding with water molecules, enhancing solubility. The length of the hydrocarbon chain can influence this property, as longer chains can introduce hydrophobic characteristics that decrease solubility.

Chain Length and Solubility

The length of the carbon chain in organic compounds significantly affects their solubility in water. As the carbon chain length increases, the hydrophobic character of the molecule also increases, which can lead to decreased solubility. In comparing compounds, shorter chains typically result in higher solubility due to a greater proportion of polar functional groups relative to the nonpolar hydrocarbon portion.

In the following pairs of compounds, which would you expect to be more soluble in water? Why?a. C8H17COOH or CH3CH2CH2COOH