How much will dissolve: saturated and unsaturated

Keep spooning sugar into your tea and at some point it just won't dissolve: it sits at the bottom. The tea has had all it can take. Is there a limit for salt in water too?

Find out (Activity 9.1). Half-fill a clean glass with water, add one spoon of salt, and stir until it disappears. Keep adding one spoon at a time, stirring each time. Count how many spoons dissolve completely, and record it in Table 9.1.

At first each spoonful vanishes. After a few, the salt stops dissolving and settles at the bottom. The water can't dissolve any more: it has reached its limit.

How much solute is in a fixed amount of solution (or solvent) is its concentration. A solution with little solute is dilute; one with a lot is concentrated. These are relative words: one spoon of salt makes a solution dilute compared with two or more spoons in the same water.

Try this: which is more concentrated, 2 spoons of salt in 100 mL of water or 4 spoons in 50 mL? Compare them over the same volume: the first is the same as 1 spoon per 50 mL, the second 4 spoons per 50 mL. The second is four times as concentrated.

The most solute that can dissolve in a fixed amount of solvent is its solubility. Solubility is always given at a particular temperature, for a reason you'll see next.