Why is isopropyl alcohol soluble in water?

1 Answer
Dec 20, 2015

Isopropyl alcohol is soluble in water because it can form strong hydrogen bonds to the water.


The solubility of an alcohol in water is a competition between two parts of the molecule: the polar #"OH"# group and the nonpolar hydrocarbon portion.

The molecule must push the water molecules apart to form a solution, breaking the hydrogen bonds in the water molecules in the process.

The energy required to break the hydrogen bonds in water is compensated by the energy that is released when water forms hydrogen bonds to the alcohol #"OH"# group.

But the alkyl portion of the molecule must separate the water molecules, with no compensating release of energy.

In isopropyl alcohol, more energy is released by forming hydrogen bonds at the #"OH"# "head" than is required to break them by the alkyl "tail".

So, isopropyl alcohol is soluble in water in all proportions.

If the alkyl group contains more than six carbon atoms, the alkyl group outweighs the #"OH"# group, and the alcohol becomes "insoluble" in water.