S OLUBILITY AND C ONCENTRATION Chapter 7.3

O BJECTIVES Explain the meaning of solubility and compare the solubility of various substances. Describe dilute, concentrated, saturated, unsaturated, and super-saturated solutions. Relate changes in temperature and pressure to changes in solubility of solid and gaseous solutes. Express the concentration of a solution as molarity, and calculate the molarity of a solution given the amount of solute and the volume of the solution.

S OLUBILITY Insoluble – will not dissolve in a solvent. Soluble – dissolves easily in a solvent. Solubility – the maximum amount of a solute that will dissolve in a given quantity of solvent at a given temperature and pressure. Not all substances are soluble in water. The solubility of any substance in water depends on the strength of the forces acting between water molecules and solute particles compared to the forces acting between the solute particles.

C ONCENTRATION Concentration refers to the amount of a particular substance in a given quantity of a mixture, solution, or ore. Concentrations are not specific… Concentrated – refers to a solution that contains a large amount of solute. Dilute – refers to a solution that contains only a small amount of solute.

U NSATURATED S OLUTIONS An unsaturated solution contains less solute than a saturated solution and is capable of dissolving additional solute. When you add more solute to an unsaturated solution, it dissolves. Eventually, adding more solute to an unsaturated solution will cause it to become saturated.

S ATURATED S OLUTIONS At some point, most solutions become saturated with solutes – meaning they will not dissolve any more solute under the given conditions. Adding more solute to a saturated solution will have zero effect on the solution. The added solute will settle to the bottom of the solution. Heating a saturated solution will enable the solution to dissolve more solute, which forms a super-saturated solution.

S UPER - SATURATED S OLUTIONS Super-saturated solution – a solution that holds more dissolved solute than is required to reach equilibrium at a given temperature. When a super-saturated solution cools down, the excess dissolved solute stays in solution. It will only crystalize if additional solute is added after the solution has cooled down.

T EMPERATURE AND P RESSURE Gaseous solutes are less soluble in warm water - meaning less solute dissolves in warm water compared to cold water. Pressure also affects the amount of gaseous solute that will dissolve. Increasing the pressure increases the amount of solute that will dissolve.

M OLARITY Molarity – an expression of the concentration of a solution in moles of dissolved solute per liter of solution. Molarity = (moles of solute)/(liters of solution) M = mol/L