Question

A .175 M weak acid solution has a pH of 3.25. Calculate the K_a for the acid. (hint your answer should contain three significant figures and be written in scientific notation ex. 4.67E-2 )

Answer 1

PH    = 3.25

-log[H^+]   = 3.25

    [H^+]     = 10^-3.25   = 0.000562

              HA(aq) ------------------> H^+ (aq)    + A^- (aq)

I             0.175                            0                    0

C              -0.000562                  0.000562       0.000562

E           0.174438                     0.000562         0.000562

                Ka     = [H^+][A^-]/[HA]

                        = 0.000562*0.000562/0.174438

                          = 1.81*10^-6    >>>>>answer