Determine whether a NH4C2H3O2 solution is acidic or basic based on Ka and Kb values. Show all calculations and reasoning.

Question

Determine whether a NH₄C₂H₃O₂ solution is acidic or basic based on Ka and Kb values. Show all calculations and reasoning.

Answer 1

is essentially the result of reaction between a weak base (NH₄OH) and a weak acid (HC₂H₃O₂), i.e. between ammonium hydroxide and acetic acid. In solution we will have NH₄⁺ and C₂H₃O₂^- (along with H2O, etc.).

So, we want to look at the hydrolysis of NH4+ and C₂H₃O₂^- and compare Ka to Kb:

NH₄⁺ + H2O ==> NH₃ + H3O⁺

The K_b for NH₃ is 1.77 x 10¯⁵ so Ka NH₄⁺ = 1x10^-14/1.77x10^-5 = 5.6x10^-10

C₂H₃O₂^- + H2O ==> HC₂H₃O₂ + OH^-

The Ka for HC₂H₃O₂ is 1.76x10^-5 so Kb C₂H₃O₂^- = 1x10^-14/1.76x10^-5 = 5.7x10^-10

Since the Ka and Kb are virtually the same, the solution should be neutral.