AP Chemistry
Name _______________________________
Ch 15 Acid-Base Reactions
B u f f e r s
C a l c u l a t i o n s
1. pH of a buffer weak acid/salt of conj. base: Calculate the pH of a buffer containing 0.75
M lactic acid HC3H5O3 (Ka = 1.4 x 10-4) and 0.25 M sodium lactate. Use the HendersonHasselbalch equation. If concentrations are very small, use ICE box.
[A - ]
pH = pKa + log
[HA]
2. pH of a buffer weak base/salt of conj. acid: Calculate the pH of a buffer containing 0.25
M NH3 (Kb = 1.8 x 10-5) and 0.40 M NH4Cl. Calculate Ka of conj. Acid (NH4+) Ka =
Kw/Kb. Use the Henderson-Hasselbalch equation with [Base]/[Conj. acid]
3. Adding strong acid to a buffer of B/BH+: Calculate the pH when 0.10 mol HCl is added
to 1.0 L of a buffer containing 0.25 M NH3 (Kb = 1.8 x 10-5) and 0.40 M NH4Cl. Calculate
initial moles B and BH+. The strong acid reacts completely with B.
H+ + B HB+
Calculate final moles of B and HB+ with stoichiometry. Calculate concentration of B and HB+
Calculate Ka of conj. Acid (NH4+) Ka = Kw/Kb. Use the Henderson-Hasselbalch equation.
4. Adding strong base to a buffer of B/BH+: Calculate pH when 0.10 mol NaOH is added
to .0 L of a buffer containing 0.25 M NH3 (Kb = 1.8 x 10-5) and 0.40 M NH4Cl. Calculate
initial moles B and BH+. The OH- reacts completely with HB+.
OH- + HB+ B
Calculate final moles of B and HB+ with stoichiometry. Calculate concentration of B and HB+
Calculate Ka of conj. Acid (NH4+) Ka = Kw/Kb. Use the Henderson-Hasselbalch equation.
5. Adding strong acid to a buffer of HA/A- OR adding strong base to a buffer of HA/A-.
Similar to above. 1. Calculate initial moles of HA and A-. 2. Use neutralization reaction
and stoichiometry to find final moles HA and A-. Use the Henderson-Hasselbalch
equation.
6. Amount of A- to add to HA for given pH: Calculate the mass of sodium acetate
NaC2H3O2 to add to 500.0 mL of 0.200 M acetic acid (Ka = 1.8 x 10-5) to give a pH of
5.00. Solve for [A-] in the Henderson-Basselbalch equation. Calculate moles A- needed
for 500.0 mL M1V1 = M2V2. Calculate grams with molar mass.