0.1 mole of CH3NH2(Kb=5 × 10−4 is mixed with 0.08 mole of HCl and
diluted to one litre. What will be the H+ concentration in the solution?
8 x 10-11 M
CH3NH2 + HCl → CH3NH+3Cl−
Initially,
CH3NH2 = 0.1, HCl = 0.08, CH3NH+3Cl− = 0
At Equilibrium,
CH3NH2 = 0.02, HCl = 0, CH3NH+3Cl− = 0.08
pOH = pK + log0.080.02
= pK + 0.602
= 3.30 + 0.602 = 3.902
∴ pH = 10.1
[H+] = 7.99 × 10−11