Question

about this time you may be wishing you had an aspirin. Aspirin is an organic acid with a ka of 3.27E-4 for the reaction HC9H7O4(aq) +H2O(L) <--> C9H7O4-(aq) +H3O+(aq) If you have two tablets each containing 0.325g of asprin (mixed with a neutral "binder" to hold the tablet together), and you dissolve them in a glass of water to give 225ml of solution, what is the ph of the solution?

Answer 1

HC9H7O4(aq) +H2O(L) <--> C9H7O4-(aq) +H3O+(aq)

Concentration of aspirin = (0.325/180.16)*(1000/225) = 0.008

HC9H7O4(aq) +H2O(L) <--> C9H7O4-(aq) +H3O+(aq)

0.008                                      0                    0

0.008-x                                   x                    x

Ka = x^2/(0.008-x)

3.27*10^-4 = x^2/(0.008-x)

x = 0.00146

[H3O+] = 0.00146

pH = -log(0.00146) = 2.83