The amount of solute that dissolves can vary SECTION 4.2

Low concentration: low amounts of dissolved solute A solution’s concentration depends on the amount of solute dissolved in a solvent at a particular temperature Low concentration: low amounts of dissolved solute High concentration: high amounts of dissolved solute

Degrees of concentration Dilute Solution: a solution that has a low concentration of solute Adding more solvent can dilute a solution (i.e. adding more water into a solution of salt water) Concentrated Solution: a solution that has a high concentration of solute Adding more solute raises the concentration of the solution Saturated Solution: a solution that contains the maximum amount of solute that can be dissolved in the solvent at a given temperature

Supersaturated solutions Sometimes, a solution contains more dissolved solute than is normally possible. Supersaturated Solution A saturated solution can become supersaturated if more solute is added while the temperature is raised

solubility Solubility: the amount of that substance that will dissolve in a certain amount of solvent at a given temperature Ex: a large amount of ammonia can dissolve in water (high solubility) Ex: only a small amount of carbon dioxide can dissolve in water (low solubility in water) Ex: Oils do not dissolve at all (insoluble) The amount of solute needed to make a saturated solution depends on the solubility of a solute in a particular solvent.

Solubility can change: Temperature Temperature increasing with a solid solute: Solute dissolves more quickly A greater amount of solute dissolves in the solvent Temperature increasing with a gaseous solute: Gas is less soluble in water

Solubility can change: pressure Pressure does not have an effect on a solid solute’s solubility. The solubility of a gas: Increases at higher pressures Decreases at lower pressures

Temperature and pressure effects on solubility Solute Increased Temperature Decreased Temperature Increased Pressure Decreased Pressure Solid Increase in solubility; faster dissolving Decrease in solubility; slower dissolving No effect on solubility Gas Decrease in solubility Increase in solubility

Solubility depends on molecular structure Water is polar, oil is nonpolar: their molecules are not attracted to each other “Like dissolves Like” Polar solvents (water) will dissolve polar solutes (sugar and salt) Nonpolar solvents will dissolve nonpolar solutes (gasoline mixtures)