Solubility & Saturation Section (8.5) Solubility & Saturation

Saturation of a Solution A saturated solution is formed when no more solute will dissolve in a solution, and excess solute is present It has the maximum amount of solute it can hold An unsaturated solution is a solution that is not yet saturated. It can still dissolve more solute

Solubility Solubility is defined as: The amount of solute that dissolves in a given quantity of solvent, at a certain temperature, to form a saturated solution Usually stated in grams of solute per 100 g of water at a given temperature. E.g. the solubility of sodium chloride in water at 20°C is 36g per 100mL of water Insoluble if solubility < 0.1g per 100 mL solvent

Solubility Recall, solubility defined as: The amount of solute that dissolves in a given volume of solvent, at a specific temperature, to form a saturated solution. For most solids: as T increases, solubility increases For most gases: as T increases, solubility decreases as P decreases, solubility decreases

Factors that Affect Rate of Dissolving Particle size: Finely divided substances have more surface area and dissolve more rapidly Motion: Stirring or shaking brings more solvent in contact with more solute particles, increasing solubility Temperature: The solubility of most solids increases with temperature. The solubility of gases decreases with temperature. It is important to note that the rate, at which a substance dissolves, does not alter the substance's solubility. If a solute is not soluble in a certain solvent, changing the conditions will not make it dissolve in the solvent.

Summary of Factors that Affect Solubility The polarity of the substances: LIKE dissolves LIKE The nature of the substances: Intermolecular bonds The temperature: Some substances only dissolve above certain temperatures The pressure: Some substances only dissolve under pressure

Solubility Curves It is possible to represent solubility visually by graphing the solubility of substances in function of temperature. The following graph, called a solubility curve, depicts the solubility of nine substances in water. Each substance is represented by its own coloured line. You will be asked to solve problems based on interpreting this graph.

Using Solubility Curves Which salt is least soluble at 40°C? NaCl K2Cr2O7 KClO3 KNO3 Which of the following decreases in solubility as the temperature increases? KCl Ce2(SO4)3 NaNO3

Using the Solubility Graph How many grams of lead (II) nitrate, Pb(NO3)2 are soluble in 100g of water at 30°C? 40g 45g 65g 130g At what temperature does the solubility of sodium chloride match the solubility of potassium chlorate? 25°C 60°C 90°C 100°C

Using the Solubility Graph When 70 g of calcium chloride are dissolved in 100 g of water at 20°C, the solution can be described as: saturated unsaturated A solution of potassium chloride has 35g of the salt dissolved in 200 g of water at 60°C. How many more grams of the salt can be added to the solution before reaching the saturation point? none, it is already saturated 15g 25g 50g