Ch 13 Ions in Aq Soln and Colligative Properties 13 Ch 13 Ions in Aq Soln and Colligative Properties 13.1 Compounds in Aq Solns Dissociation: separation of ions when it dissolves Use the coefficients on the balanced eqn NaCl (s)  Na + (aq) + Cl – (aq)

Precipitation Rxns Figure 1.3 (pg 413) Not all ionic compounds are soluble in water Ionic compounds with very low solubility are insoluble Use basic rules to predict solubility Ex: soluable NaNO3 K3PO4 (NH4)2S insoluable HgCl BaSO4

Net Ionic Eqns Only compounds that undergo chemical change, removes spectator ions Spectator ions not involved in chemical reaction Example pg 416

Ionization: solute dissolved in solvent that forms ions When molecular compounds form ions in soln These molecular compounds tend to be polar Not same as dissociation bc there were already ions present in dissociation reaction Ionization makes ions from previously neutral Hydronium Ion: H+ ion forms H3O+ ion When molecular compounds ionize they release H+ H+ ions attracts other ions/molecules so strongly it doesn’t typically exist alone

An electrolyte’s strength depends on how many dissolved ions it has! Strong Electrolytes: conduct electricity well, all/most dissolved compound is ions HF(aq) + H2O(l) ↔ H3O+(aq) + F-(aq) Weak Electrolytes: conduct electricity poorly, small amount dissolved compound is ions CH3COOH(aq) + H2O(l) ↔ CH3COO-(aq) + H3O+(aq)

13.2 Colligative Properties of Solutions Recall: colligative properties depend on concentration of solute particles Lowering vapor pressure depends on nonelectrolyte solute concentration Nonvolatile substance is unlikely to become a gas under current conditions 2.1 pg 422

Solutions with nonelectrolyte solute will have: Lowered freezing points Molal Freezing-point constant: Kf Freezing point depression: Δtf = Kfm *Just change in temp subtract from normal freezing pt Higher boiling points Molal boiling-point constant: Kb Boiling point depression: Δtb = Kbm *Just change in temp ADD to normal boiling point!

Freezing point depression prob 425-426 “Steps” Convert g to mol Calculate molality Write net ionic equn Calculate molality of solution for # moles ions Substitute values into formula (freezing/melting) Freezing point depression prob 425-426

Recall: Osmosis is the movement from high to lower concentration of solute Osmotic Pressure Determined by concentration of dissolved solute Pressure that must be added to stop osmosis (movement through membranes) Semipermeable membrane: allows passage of some particles and blocks other particles

Total molality Determines changes in colligative properties Calculated values are only expected values, actual values may be different because of how ions behave PD 3 STOPED HERE