Solubility

Solubility in the general sense refers to the property of being soluble—being able to dissolve, usually in a liquid. Chemists, however, use the word solubility to also mean the maximum amount of a chemical substance that dissolves in a given amount of solvent at a specific temperature.

How much sugar could you dissolve in a cup of hot coffee? Certainly one teaspoonful would mix into the liquid and disappear quite easily. But after trying to dissolve several more teaspoonfuls, there will come a point where the extra sugar you add will simply not dissolve. No amount of stirring will make the sugar disappear and the crystals just settle down to the bottom of the cup. At this point the coffee is said to be saturated—it cannot dissolve any more sugar. The amount of sugar that the coffee now holds is "the solubility of sugar in coffee" at that temperature.

A sponge gets saturated when you are using it to wipe up spilled milk from a kitchen counter. At first, a dry sponge soaks up milk very quickly. But with further use, the sponge can only push milk along the counter-its absorbing action is lost. This sponge is now holding its maximum amount of milk. Similarly, a saturated solution is one that is holding its maximum amount of a given dissolved material.

The sugar you add to a cup of coffee is known as the solute. When this solute is added to the liquid, which is termed the solvent, the dissolving process begins. The sugar molecules separate and diffuse or spread evenly throughout the solvent particles, creating a homogeneous mixture called a solution. Unsaturated solutions are able to dissolve more solute, but eventually the solution becomes saturated.