Question #20ab2

1 Answer
Sep 25, 2016

Clearly, we speak of water solubility.


Alkanes have no functional group that can be effectively solvated by the water molecule. On the other hand, an aldehyde possesses a terminal carbonyl group #RC(=O)H# that can be solvated by water to allow some solubility. On the other, other hand, short chain alcohols, methanol, and ethanol, are effectively half a water molecule, and the influence of the hydroxyl group dictates their miscibility with water.

From the earliest lessons in chemistry, we learn that #"like dissolves like"#. This is certainly illustrated by the water solubility of #"ethane"#, which is much less water soluble than #"acetaldehyde"#, which is much less water soluble than #"ethanol"#.

As the chain length of the alcohol grows, the solubility of #ROH# will likewise DECREASE in water, as the interaction between the hydrocarbyl tails becomes significant. On the other hand, while #"ethanol"# is miscible with hexanes, #"methanol"# is immiscible with this solvent, and will form a layer below the hydrocarbon, just as water would. Can you account for these phenomena?