Solutions

Some definitions…. Solution: homogeneous mixture of at least two substances where each retains its own chemical identity Solvent: the component of a solution that is in greatest amount Solute: the component(s) of a solution that is/are less abundant than the solvent

Solubility The maximum amount of solute that will dissolve in a given amount of solvent under a given set of conditions

How do the following factors influence solubility? Temperature (solid in a liquid) (gas in a liquid) Pressure (gas in a liquid) Amount of solute present

Saturation Saturated: solution has the maximum amount of solute dissolved under the conditions it is at Unsaturated: solution has less than the maximum amount of solute that can be dissolved under the conditions it is at Supersaturated: unstable solution that has more solute than can normally be held under the given conditions

Dissolving and Saturation At saturation, the dissolving process does not stop. Rather it reaches a dynamic equilibrium (solute enters and leaves the solution at the same rate)

Concentrated vs Dilute Concentrated vs dilute: depends on the amount of solute present compared to how much is capable of dissolving

Aqueous solutions and the dissolving process Aqueous solutions: solutions in which water is the solvent i.e. NaCl (aq) Hydration: water molecules interrupt attractions within the solute and surround the solute components bringing them into solution Ionic compounds “dissociate” into ions while covalent compounds stay intact

Dissolving Process Rule of thumb: “likes dissolve likes” Polar solvents typically dissolve: Polar solutes or ionic solutes What types of interactions are occurring?

Solubility “Rules”

Using solubility rules to predict precipitation reactions Write the compounds present on the reactant side Dissociate them into ions Ask if the cation of one will precipitate (form an insoluble solid) with the anion of the other If so: it is a solid product If not: spectator ions Write the net equation

Units of concentration Percent by mass: g solute / 100 g solution Percent by volume: mL solute / 100 mL solution Mass-volume percent: g solute / 100 mL solution Molarity: (M) moles solute / liter solution

Calculations Concentration x volume = solute amount Re-write % as g / 100 mL Re-write M as moles / L Try some

Dilution calculations C 1 V 1 = C 2 V 2 C can be molar or percent but must be the same on both sides Volume can be any unit but must be the same on both sides Try some

Colligative properties Properties of solutions that depend on the concentration of dissolved solute particles present but not its identity Hypertonic Hypotonic Isotonic Osmosis Dialysis

More Colligative Properties Boiling point elevation Freezing point depression

Electrolytes Solutes that when dissolved, conduct electricity Must ionize Examples: ionic compounds, acids and bases