A 0.140 M solution of a weak base has a pH of 11.25.
Determine Kb for the base.
We’re asked to determine the Kb for a 0.140 M solution of a weak base with a pH of 11.25.
Recall that the Equilibrium reaction of any weak base, B in water is given by:
B(aq) + H2O(l) ⇌ HB+(aq) + OH-(aq)
• B →weak base → proton acceptor
• H2O → will act as the weak acid → proton donor
We write the Kb expression for a weak base, B as:
Since we’re dealing with a weak base and Kb is an equilibrium expression we will have to create an ICE chart to determine the equilibrium concentration of each species: