Question

In a 0.57 M solution of propanoic acid HOC6H5, 0.0684% of the acid has dissociated.

a. Find the concentrations of all aqeous species in the solution at equilibrium.

b. Find the pH of the solution

c. What concentration of HBr would produce a solution with the same pH as a 0.57 M solution of propanoic acid HOC6H5. Justify your answer.

Answer 1

First of all, there is error in the question. Propanoic acid is HO2C3H5 and not HOC6H5. Thus we will solve the question using correct formula of propanoic acid i.e.

Dissociation will take place as:

Initial concentrations are: = 0.57 M and initial concentration of reactants is 0

(a) After 0.0684% dissociation, concentrations are to be decreased(-) and increased(+) as:

Thus, concentrations at equilibrium would be:

(B) pH = -log(H+) = = 3.42

(C) Same pH means pH should be 3.42 which directly concludes that

HBr is a strong acid, it ionizes completely in the solution. When acid ionizes completely, all molecules of acid donate proton to water.

This means, if acid ionized completely, the initial concentration of HBr should be equal to H+ and Br- concentration.

Thus here