Acid/Base Titrations

Titrations Titration Curve – always calculate equivalent point first Strong Acid/Strong Base Regions that require “different” calculations B/F any base is added Half-way point region At the equivalence point After the equivalence point

Strong Acid/Strong Base 50 mL of M KOH Titrated with M HBr First -find Volume at equivalence M 1 V 1 = M 2 V 2 (0.050 L)( M) = V V = 10.0 mL

Strong Acid/Strong Base mL of M KOH Titrated with M HBr Second – find initial pH pH = - logA H ~ -log [H + ] pOH = -logA OH ~ -log [OH - ] pH = 12.30

Strong Acid/Strong Base 50 mL of M KOH Titrated with M HBr Third– find pH at mid-way volume KOH (aq) + HBr (aq) -> H 2 O (l) + KBr(aq) Before After mol mol mol0 mol Limiting Reactant mol pH = 11.8 (~6 ml)

Strong Acid/Strong Base 50 mL of M KOH Titrated with M HBr Fourth – find pH at equivalence point KOH (aq) + HBr (aq) -> H 2 O (l) + KBr(aq) Before After mol mol 0 mol mol pH = 7.0

Strong Acid/Strong Base 50 mL of M KOH Titrated with M HBr Finally – find pH after equivalence point KOH (aq) + HBr (aq) -> H 2 O (l) + KBr(aq) Before After mol mol 0 mol mol mol pH = ml Limiting Reactant

Titration of WEAK acid with a strong base

Titration of a weak acid solution with a strong base mL of M acetic acid K a = 1.8 x Titrant = M NaOH First, calculate the volume at the equivalence-point M 1 V 1 = M 2 V 2 ( L) M = M (V 2 ) V 2 = L or 25.0 mL

Titration of a weak acid solution with a strong base mL of M acetic acid K a = 1.8 x Titrant = M NaOH Second, Calculate the initial pH of the acetic acid solution

Titration of a weak acid solution with a strong base mL of M acetic acid K a = 1.8 x Titrant = M NaOH Third, Calculate the pH at some intermediate volume

Titration of a weak acid solution with a strong base mL of M acetic acid K a = 1.8 x Titrant = M NaOH Fourth, Calculate the pH at equivalence

Titration of a weak acid solution with a strong base mL of M acetic acid K a = 1.8 x Titrant = M NaOH Finally calculate the pH after the addition 26.0 mL of NaOH

Initial pH Buffer Region Equivalence point M 1 V 1 =M 2 V 2 equivalence? pH after equivalence?

Initial pH Buffer Region Equivalence point M 1 V 1 =M 2 V 2 equivalence pH after equivalence?

Initial pH Buffer Region Equivalence point M 1 V 1 =M 2 V 2 equivalence pH after equivalence Dominated by remaining [OH - ]

Weak Base titrated with strong acid Consider a 100 ml of a M base with M HCl K b = 1 x 10 -5

Initial pH Buffer Region equivalence pH after equivalence Dominated by remaining [H + ]