1. Calculate the pH of a solution that is 0
Calculate the pH of a solution that is M in Benzoic acid (HC7H5O2) and 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]}

2. pOH = 5.29 and pH = 8.71 X = [OH1-] = 5.1 x 10-6
Calculate the pH of a solution that is M in hydrazine (N2H4) and M in its conjugate acid (N2H5Cl ). The Kb of hydrazine is 1.7 x 10-6.
What the chemistry?
Dissociate the salt:
N2H5Cl → N2H Cl-
Write equilibrium expression for the weak base:
N2H4 + H2O ↔ N2H OH- I
C. -x x x
E – x x x
pOH = and pH = 8.71
X = [OH1-] = 5.1 x 10-6
Or with the Henderson Hasselbach equation: