Question

Rationalize the trend in water solubility for the following simple alcohols:

Short answer

The trend in water solubility for simple alcohols can be rationalized by considering the balance between hydrogen bonding and hydrophobic effects. Smaller alcohols have high solubility in water due to their ability to engage in hydrogen bonding with water molecules. However, as the size of the alcohol increases, the hydrophobic effect becomes more significant, causing the solubility to decrease. Larger alcohols have a greater tendency to aggregate due to their hydrophobic portions, further reducing their solubility in water.

Step-by-step solution

Identify the main factors affecting solubility in water for simple alcohols

To rationalize the trend in water solubility for simple alcohols, we need first to identify the main factors that affect solubility: 1. Hydrogen bonding: Alcohols can engage in hydrogen bonding with water molecules due to the presence of the hydroxyl (-OH) functional group. 2. Molecular size: As the number of carbon atoms in the alcohol's chain increases, its size and hydrophobicity also increase. 3. Hydrophobicity: Larger alcohols have a high tendency to aggregate together and separate from water due to the hydrophobic effect, thus leading to reduced solubility.

Understand the role of hydrogen bonding in water solubility

Hydrogen bonding occurs between the highly electronegative oxygen atom in the hydroxyl (-OH) group of the alcohol and the hydrogen atom of a water molecule. This interaction leads to the attraction between alcohol and water molecules, which promotes solubility. The ability to engage in hydrogen bonding is a significant factor in the solubility of small alcohols in water.

Examine the impact of molecular size on solubility

As the size of the alcohol's hydrocarbon chain increases, its solubility in water decreases due to the hydrophobic nature of the carbon chain. The nonpolar portion of larger alcohols minimizes interactions with polar water molecules, lowering their solubility. For example, the solubility of methanol (CH3OH) is high in water, while the solubility of octanol (C8H17OH) is lower.

Take hydrophobicity into account when analyzing solubility trends

Hydrophobicity further contributes to the decrease in solubility as the alcohol chain size increases. As more carbon atoms are added to the hydrocarbon chain, the nonpolar regions of the molecule interact with each other and aggregate, leading to the formation of clusters. This effect reduces the surface area available for hydrogen bonding with water molecules, which consequently decreases solubility.

Rationalize the trend in water solubility for simple alcohols

Now that we understand the factors affecting the solubility of alcohols in water, we can rationalize the trend by considering the balance between hydrogen bonding and hydrophobic effects: - Smaller alcohols have a high tendency to engage in hydrogen bonding, resulting in high solubility in water. - As the size of the alcohol increases, the hydrophobic effect becomes more significant, leading to reduced solubility in water. - Larger alcohols have a greater tendency to aggregate due to the hydrophobic portions of the molecules interacting, further reducing their solubility in water. In summary, the trend in water solubility for simple alcohols can be rationalized by comparing the strengthening of the hydrophobic effect to the relative importance of hydrogen bonding interactions as the size of the alcohol's hydrocarbon chain increases.