Solubility

Common Measuring Units

Solubility is often expressed in grams of solute per 0.2 lb (100 g) of solvent, usually water. At 122°F (50°C), the solubility of sugar in water is approximately 130 g/sugar in 100 g water. If you were to add 0.26 lb Figure 1. Solubility curve for various solutes in water. Illustration by Hans & Cassidy. Courtesy of Gale Group. (130 g) of sugar to 0.2 lb (100 g) of water at 122°F (50°C), the resulting solution would be saturated. Adding 0.26 lb (131 g) would mean that even with continuous stirring, 0.002 lb (1 g) of sugar would remain at the bottom of your container.

Sometimes, solubility is expressed as grams of solute per 0.2 lb (100 g) of solution. In this case the value of the solubility of sugar in 0.2 lb (100 g) of solution at 122°F (50°C) would be less than 0.26 lb (130 g), because unlike the previous example where the weight of the solvent was fixed, the weight of a solution changes as solute is added.

Other commonly used units include g/L (grams of solute per liter of solution) and m/L (moles of solute per liter of solution). Solubility units always express the maximum amount of solute that will dissolve in either a given amount of solvent, or a given amount of solution, at a specific temperature.