Physical Properties of Alkohols

Boiling Points

1. The boiling point of alcohol is always much higher than that of the alkane with the same number of carbon atoms.
2. This is because, the presence of the hydroxyl group gives extra force between the molecules, hence more heat energy is needed to overcome the intermolecular force when boiling.
3. The boiling points of the alcohols increase as the number of carbon atoms increases.
4. This can be explained by the following:
1. the number of carbon increases, the size of the molecule increases.
2. intermolecular force increases.
3. more heat energy is needed to overcome the intermolecular force.

The solubility of Alcohols in Water

1. The small alcohols are entirely soluble in water.
2. However, solubility falls as the length of the hydrocarbon chain in the alcohol increases.
3. Explanation:
1. Every alcohol consists of two parts, the hydrocarbon chain which is not soluble in water, and the hydroxyl functional group, which is soluble in water.
2. In short-chain alcohol, the hydroxyl group plays a significant part in forming forces (hydrogen bond) in between water and alcohol molecule, therefore they are soluble in water.
3. For the long-chain alcohol, the hydroxyl group is just a small part of the molecule. Therefore, the insoluble long hydrocarbon chain contributes more to the forces between water and alcohol molecule, causes the solubility to decrease.