The following graph shows the solubility of some alkan-1-ols in water at 20°C - HSC - SSCE Chemistry - Question 29 - 2023 - Paper 1

As the molar mass of alkan-1-ols increases, the chain length of the alcohols also increases. This trend shows that the solubility of alkan-1-ols in water decreases with longer chain lengths.

Short-chain alkan-1-ols, which have fewer carbon atoms, are able to form stronger hydrogen bonds between the hydroxyl (–OH) group and the water molecules. These interactions promote solubility in water. However, as the chain length increases, the hydrophobic character of the alkyl groups becomes more pronounced, leading to a decrease in solubility.

The intermolecular forces involved include:

• Hydrogen bonds: Present in the interactions between the hydroxyl group of the alcohols and water, facilitating solubility in shorter chains.
• Dispersion forces: These forces become more significant as the length of the carbon chain increases, counteracting the hydrogen bonding effect and reducing solubility. Thus, the trend illustrated in the graph can be attributed to the competition between these types of intermolecular forces.