Iodine solution

As iodine is a non-polar molecule it is only sparingly soluble in water (which is polar) giving a pale yellow solution. In the laboratory we usually use iodine in potassium iodide solution. Iodine is much more soluble in potassium iodide solution as it interacts with the iodide ion to produce an ion which dissolves readily in water:

I₂(aq) + I^-(aq) ⇒ I₃^-(aq)

The colour of this solution depends on the quantity of iodine dissolved and can vary from pale yellow to dark brown.

Iodine also dissolves readily in ethanol. This solution is called tincture of iodine, and is used in the home as an antiseptic.

We shall see that iodine also dissolves readily in non-polar, hydrocarbon solvent. This is useful in distinguishing between solutions of iodine and bromine.