Concentration limits

Solubility is the maximum amount of solute that will dissolve in a given amount of a solvent at a specified temperature. You know from your own experiences, I’m sure, that there’s a limit to how much solute you can dissolve in a given amount of solvent. Most people have been guilty of putting far too much sugar in iced tea. No matter how much you stir, some undissolved sugar stays at the bottom of the glass.

Solubility normally has the units of grams solute per 100 milliliters of solvent (g/100 mL), and it’s related to the temperature of the solvent:

✓ Solids in liquids: For solids dissolving in liquids, solubility normally increases with increasing temperature. For instance, if you heat that iced tea, the sugar at the bottom will readily dissolve.

✓ Gases in liquids: For gases dissolving in liquids, such as oxygen dissolving in lake water, the solubility goes down as the temperature increases. This is the basis of thermal pollution, the addition of heat to water that decreases the solubility of the oxygen and affects the aquatic life.