Identify the compound in each group that is most soluble in water. Explain.
b. ethanoic acid (acetic acid), hexanoic acid, octanoic acid

Verified step by step guidance

1. Step 1: Understand the concept of solubility in water. Water is a polar solvent, meaning it dissolves polar compounds and those capable of hydrogen bonding more effectively than nonpolar compounds.
2. Step 2: Analyze the molecular structure of each compound. Ethanoic acid (acetic acid), hexanoic acid, and octanoic acid are all carboxylic acids, which contain a polar carboxyl (-COOH) group capable of hydrogen bonding with water molecules.
3. Step 3: Consider the impact of the hydrocarbon chain length on solubility. As the hydrocarbon chain length increases, the compound becomes more nonpolar, reducing its overall solubility in water. Ethanoic acid has the shortest chain, hexanoic acid has a medium chain, and octanoic acid has the longest chain.
4. Step 4: Compare the compounds based on their polarity. Ethanoic acid, with its shorter chain, is more polar and has a higher proportion of its structure capable of interacting with water molecules compared to hexanoic acid and octanoic acid.
5. Step 5: Conclude that ethanoic acid (acetic acid) is the most soluble in water among the three compounds due to its shorter hydrocarbon chain, which minimizes the nonpolar portion of the molecule and maximizes its ability to hydrogen bond with water.

Key Concepts

Polarity

Polarity refers to the distribution of electrical charge over the atoms in a molecule. Polar molecules, which have a significant difference in electronegativity between their atoms, tend to dissolve well in water due to hydrogen bonding. In the context of the given acids, the more polar the molecule, the higher its solubility in water.

Hydrogen Bonding

Hydrogen bonding is a type of intermolecular force that occurs when a hydrogen atom covalently bonded to a highly electronegative atom, like oxygen, interacts with another electronegative atom. This interaction significantly increases the solubility of compounds in water, as seen with ethanoic acid, which can form hydrogen bonds with water molecules, enhancing its solubility compared to less polar compounds.

Chain Length and Solubility

The chain length of a fatty acid affects its solubility in water. Shorter-chain fatty acids, like ethanoic acid, are more soluble due to their ability to interact more effectively with water molecules. In contrast, longer-chain fatty acids, such as hexanoic and octanoic acids, have increased hydrophobic character, which reduces their solubility in water.