If the solubility of KCl in 100 mL of H₂O is 34 g at 20 °C and 43 g at 50 °C, label each of the following solutions as unsaturated, saturated, or supersaturated. If more solid is added then can dissolve in the solvent, assume undissolved solid remains at the bottom of the flask.

a) adding 30 g to 100 mL of H₂O at 20 °C

b) adding 65 g to 100 mL of H₂O at 50 °C

c) adding 42 g to 100 mL of H₂O at 50 °C and slowly cooling to 20 °C to give a clear solution with no precipitate

a) Unsaturated

b) Supersaturated

c) Unsaturated

Explanation:

A saturated solution contains the maximum amount of a solute that will dissolve in a given solvent at a specific temperature.

An unsaturated solution contains less solute than it has the capacity to dissolve.

A supersaturated solution, contains more solute than is present in a saturated solution. Supersaturated solutions are not very stable. In time, some of the solute will come out of a supersaturated solution as crystals.

According to these definitions and considering that the solubility of KCl in 100 mL of H₂O at 20 °C is 34 g, and at 50 °C is 43 g we can label the solutions:

a) 30 g in 100 mL of H₂O at 20 °C ⇒ unsaturated

b) 65 g in 100 mL of H₂O at 50 °C ⇒ supersaturated

c) 42 g in 100 mL of H₂O at 50 °C and slowly cooling to 20 °C to give a clear solution with no precipitate ⇒ unsaturated (if it were saturated it would have had precipitate)