CN- is the conjugate base of a weak acid and NH4+ is the
conjugate acid of a weak base
CNHCN(aq) + H2O(l) ⇌ H3O+(aq) + CN-(aq) Ka = 6.2x10-10
NH4+
NH3(aq) + H2O(l) ⇌ NH4+(aq) + OH-(aq) Kb = 1.8x10-5
Will the following solutions be acidic, basic, or neutral?
1. NaCl(aq)  Na+(aq) + Cl-(aq)
2. KCN(aq)  K+(aq) + CN-(aq)
3. NH4NO3(aq)  NH4+(aq) + NO3-(aq)
1
Example Problem
What is the pH of a 0.035M solution of Ca(NO2)2?
2