Answer to Question #164754 in General Chemistry for John Lawrence

Question

 354.50 mL of the following solutions are kept in equilibrium at 250C. Write the pertinent chemical equilibria involved and calculate for their pH.

a. 0.25M maleic acid in 0.05M sodium maleate;

b. 2.71 x 10-3M succinic acid;

c. 0.050M citric acid

Answer 1

pH is the negative log of the concentration of H3O+. If you are given the Ka of a weak acid, the equation is Ka=[(concentration of conjugate base)*(concentration of H3O+) ]/[(concentration of conjugate acid -concentration of conjugate base)]. This can be simplified (assuming Ka is quite small) to

Ka= [concentration of H3O]^2 / [concentration of conjugate acid]

Then, rearrange the equations to get the concentration of H3O+. Take the negative log of that number and that is your pH.