Titrations In a titration a solution of accurately known concentration (titrant) is added gradually added to another solution of unknown concentration (analyte) until the chemical reaction between the two solutions is complete. Equivalence point – the point at which the reaction is complete - balance point. Indicator – substance that changes color at (or near) the equivalence point. Slowly add base to unknown acid UNTIL The indicator changes color (pink) 4.7

Strong Acid-Strong Base Titrations NaOH (aq) + HCl (aq) H 2 O (l) + NaCl (aq) OH - (aq) + H + (aq) H 2 O (l) 0.10 M NaOH added to 25 mL of 0.10 M HCl 16.4 => Neutral pH small buffer zone

Weak Acid-Strong Base Titrations CH 3 COOH (aq) + NaOH (aq) CH 3 COONa (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq) CH 3 COO - (aq) + H2O (l) CH 3 COO - (aq) + H 2 O (l) OH - (aq) + CH 3 COOH (aq) At equivalence point (pH > 7): 16.4 Inflection point (steepest slope) Basic pH large buffer zone => slow change in pH

Strong Acid-Weak Base Titrations HCl (aq) + NH 3 (aq) NH 4 Cl (aq) NH 4 + (aq) + H 2 O (l) NH 3 (aq) + H + (aq) At equivalence point (pH < 7): 16.4 H + (aq) + NH 3 (aq) NH 4 Cl (aq) Acidic pH large buffer zone => slow change in pH

Titrations Acid + Base Salt + Water Can do any combination Strong Acid Strong Base Weak Acid Weak Base Weak acid with weak base is not preferable (two buffer zones). Can start with either acid or base in flask. => Looking to calculate the equivalence point where acid concentration = base concentration Polyprotic acids will have multiple equivalence points.

Effect of K a on Titration Curve Relatively flat Much more curvature and equivalence point rises as K a gets smaller