Solutions & Molarity What is a solution? Solution – homogeneous mixture Solvent – substance present in largest amount Solutes – other substances in the solution Aqueous solution – solution with water as the solvent

Solubility Solubility of Ionic Substances Ionic substances breakup into individual cations and anions.

Solubility How Substances Dissolve A “hole” must be made in the water structure for each solute particle. The lost water-water interactions must be replaced by water-solute interactions. “like dissolves like”

Solution Composition: An Introduction The solubility of a solute is limited. Saturated solution – contains as much solute as will dissolve at that temperature Unsaturated solution – has not reached the limit of solute that will dissolve

Solution Composition: An Introduction Supersaturated solution – occurs when a solution is saturated at an elevated temperature and then allowed to cool but all of the solid remains dissolved Contains more dissolved solid than a saturated solution at that temperature Unstable – adding a crystal causes precipitation

Solution Composition: An Introduction Solutions are mixtures. Amounts of substances can vary in different solutions. Specify the amounts of solvent and solutes Qualitative measures of concentration concentrated – relatively large amount of solute dilute – relatively small amount of solute

Solution Composition: An Introduction Which solution is more concentrated?

Solution Composition: An Introduction Which solution is more concentrated?

Solution Composition: Molarity Concentration of a solution is the amount of solute in a given volume of solution.

Solution Composition: Molarity Consider both the amount of solute and the volume to find concentration.

Solution Composition: Molarity Standard solution - a solution whose concentration is accurately known To make a standard solution Weigh out a sample of solute. Transfer to a volumetric flask. Add enough solvent to mark on flask.

Boiling Point and Freezing Point The presence of solute “particles” causes the liquid range to become wider. Boiling point increases Freezing point decreases

Boiling Point and Freezing Point Why does the boiling point of a solution increase? Forming a bubble in a solution Solute particles block some of the water molecules trying to enter the bubble. Need higher pressure to maintain the bubble.

Boiling Point and Freezing Point Colligative property – a solution property that depends on the number of solute particles present