Salt Solutions & Titration - Chemistry PDF

Salt solutions Reactions of ions with water: hydrolysis  Hydrolysis Hydration: the interaction of ions with water molecules. Solvation: the interaction of ions with the molecules of a solvent. Hydrolysis: the reaction of an ion with water. An ion can react with water, so ca...

Salt solutions Reactions of ions with water: hydrolysis  Hydrolysis Hydration: the interaction of ions with water molecules. Solvation: the interaction of ions with the molecules of a solvent. Hydrolysis: the reaction of an ion with water. An ion can react with water, so can hydrolyze only if it is the conjugate pair of a weak acid or a weak base.  Reactions of ions with water: hydrolysis Ka  Kb = Kw Strong acid shifted to the right HA + H2O ⇌ H3 O+ + A acid conjugate base Weak acid shifted to the left If HA is strong, its Ka is immeasurable large  Kb of A- is zero, so A- cannot hydrolyze. If HA is weak, its Ka is measurable  Kb of A- bigger than zero, so A- can hydrolyze. B + H2O ⇌ BH+ + OH Strong base shifted to the right base conjugate acid Weak base shifted to the left If B is strong, its Kb is immeasurable large  Ka of BH+ is zero, so BH+ cannot hydrolyze. If B is weak, its Kb is measurable  Ka of BH+ bigger than zero, so BH+ can hydrolyze.  Conjugate pairs of strong acids and bases Conjugate pairs of strong acids and strong bases cannot hydrolyze. Examples: Cl + H2O no reaction NO3 + H2O no reaction Na+ + H2O no reaction K+ + H2O no reaction  Conjugate pairs of weak acids and bases Conjugate pairs of weak acids and weak bases can hydrolyze. Examples: F + H2O ⇌ HF + OH base acid NO2 + H2O ⇌ HNO2 + OH base acid NH4+ + H2O ⇌ NH3 + H3O+ acid base  Acidity-basicity of aqueous solutions of salts Conjugate acids or bases having Ka or Kb bigger than zero can react with water, so can hydrolyze. Salt of a... Example Cation Anion Hydrolysis Solution strong A & NaCl Ka  0 Kb  0 No. neutral strong B strong A & cation: NH4Cl Ka > 0 Kb  0 acidic weak B BH+ + H2O ⇌ B + H3 O+ weak A & anion: NaHCO3 Ka  0 Kb > 0 basic strong B A + H2O ⇌ HA + OH Both the cation and the Depends weak A & anion hydrolyze: NH4HCO3 Ka > 0 Kb > 0 on Ka weak B H3O+ and OH and Kb  Examples NaHCO3 Na+ + H2O no reaction HCO3 + H2O ⇌ H2CO3 + OH Basic solution base acid NH4NO3 NH4+ + H2O ⇌ NH3 + H3O+ acid base Acidic solution NO3 + H2O no reaction KBr K+ + H2O no reaction Neutral solution Br + H2O no reaction Answer the questions Acid-base titration  Acid-base titration Titration is a procedure for determining the amount of a substance by adding a measured volume of a solution with known concentration of another substance until the reaction of the substances is just complete. (Volumetric analysis.) Titration is a method of quantitative chemical analysis. Acid-base titration: a titration that is based on an acid-base (neutralization) reaction.  Acid-base titration Stock solution: End point: aliquot indicator Three-four parallel measurements should be made:  Acid-base titration curve An acid-base titration curve is a plot of the pH of the solution of acid (or base) against the volume of added base (or acid). Equivalence point: the point of the titration when stoichiometric amount of reactant has been added. Titration of a strong acid by a strong base Equivalence point at pH 7: salt of a strong acid and a strong base Answer the questions