Lesson 4: Solubility and Saturation

Degrees of Saturation

Unsaturated solution is a solution in which more solute can be dissolved at a given temperature and pressure.

Saturated solution is a solution that contains the maximum quantity of solute at a given temperature and pressure.

Supersaturated solution is a solution that contains more than the maximum quantity of solute that it should at a given temperature and pressure.

Solubility Curves

A solubility curve is a graph of the solubility of a substance over a range of temperature.

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Solubility Curves of Ionic Compounds

Determining a Solute Mass

A potassium sulfate solution, K2SO4(aq) containing 11.8 g/100 g H2O at 20 ℃ is warmed to 60℃. What additional mass is required to saturate the solution?

Saturation mass at 60 ℃ = 18.4 g/100g H2O

Saturation mass at 20℃ = 11.8 g/100g H2O

Find the difference

18.4 - 11.8 = 6.6 g/100 g H2O

Therefore, an additional 6.6 g/100g H2Oof potassium sulfate is required to make a saturated solution

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Solubility Curves of Gases

Unlike with solids, the solubility of gases decreases as the temperature rises.

This happens due molecules of gas being dissolved are able to escape the solution as the temperature increases and float away in the atmosphere

Summary

The solubility of a solution is expressed as the mass of the solute required to form a saturated solution in 100g (100 mL) of water at a given temperature.

Solutions may be unsaturated, saturated, or supersaturated depending on the quantity of solute they hold at a given temperature and pressure.

A solubility curve  shows the solubility of a solute in a specific solvent over a range of temperatures.

The solubility of solids generally increases as the temperature increases, while the solubility of gases decreases.

The solubility of a gas increases as the applied pressure increases.  Pressure has no significant effect on the solubility of solids and liquids