Calculate the pH of a solution that is 0 Calculate the pH of a solution that is 0.150 M in Benzoic acid (HC7H5O2) and 0.050 M in potassium benzoate (KC7H5O2). The pKa of benzoic acid is 4.20) This is a buffer solution since it contains a weak acid and its conjugate base (a salt of the acid). What is the equilibrium chemical equation? KC7H5O2 dissociates in water to K+ and C7H5O2- The acid establishes an equilibrium. HC7H5O2 + H2O ↔ H3O+ + C7H5O2- Since this is a buffer solution, the Henderson-Hasselbalch equation can be used: pH = pKa + Log{[conj. Base])/[Acid]}

pOH = 5.29 and pH = 8.71 X = [OH1-] = 5.1 x 10-6 Calculate the pH of a solution that is 0.150 M in hydrazine (N2H4) and 0.050 M in its conjugate acid (N2H5Cl ). The Kb of hydrazine is 1.7 x 10-6. What the chemistry? Dissociate the salt: N2H5Cl → N2H5+ + Cl- Write equilibrium expression for the weak base: N2H4 + H2O ↔ N2H5+ + OH- I. 0.150 0.050 0 C. -x +x +x E. 0.150 – x 0.050 + x +x pOH = 5.29 and pH = 8.71 X = [OH1-] = 5.1 x 10-6 Or with the Henderson Hasselbach equation: