Question

Would you expect octane to be soluble in cyclohexane (another hydrocarbon)? Explain your answer.

As the number of carbons in a linear alcohol increases from one C in methanol to 8 C in 1-octanol, what do you predict occurs with water solubility?

As the number of carbons in a linear alcohol increases from one C in methanol to 8 C in 1-octanol, what do you predict occurs with cyclohexane solubility?

As the number of alcohol groups in a molecule increases, what do you expect happens to the water solubility?

In general, if the solubility in water decreases, what do you expect happens to solubility in cyclohexane?

Predict cyclohexanol solubility in water and in cyclohexane. Explain your predictions

Answer 1

Like dissolves like. According to this theory, polar solvents dissolve polar compounds and non-polar compounds dissolves non-polar compounds. Octane and cyclohexane, both are hydrocarbons and also both non-polar in nature, hence octane is expected to be soluble in cyclohexane.

Increasing number of carbons from methanol to 1-octanol increases non-polar nature in the alcohol. Water being a polar solvent, should have a decreasing dissolving power for 1-octanol compared to methanol i.e. water solubility will decrease from methanol to 1-octanol.

Cycolhexane is a non-polar solvent, so increasing non-polar nature should increase its solubility in cyclohexane-like non-polar solvent. Hence, as explained earlier, cyclohexane solubility will increase from methanol to 1-octanol.

As the number of alcohol groups in a molecule increase, the polar nature of the whole molecule also increase because the hydroxyl group adds to the polar nature of the molecule (O-H being highly polarised due to difference in electronegativity). That is expected to increase its solubility in water like polar solvent. Also, with increasing number of -OH groups, there are higher probability of intermolecular hydrogen bond formation between the -OH of the solute and -OH of the solvent. This increasing nonbonding interaction also favours the increasing solubility of the compound in water.

Increased solubility in water(polar solvent) means the increased polar nature of the solute compound. Hence, the same compound should show a reduced trend of solubility in a non-polar solvent like cyclohexane.

Cyclohexanol contains the cyclohexane ring and a -OH group. Due to the presence of the -OH group (high electronegativity difference between O and H) which is highly polarized itself, the compound is expected to be quite soluble in water, another polar compound. But, in cyclohexane, which is a highly non-polar compound, the solubility is expected to be much less or insignificant (at most, they will be miscible) due to their opposite nature.