Question

Calculate the pH of 1.00 x 10^-2 M oxalic acid solution. Calculate the pH of 1 x 10^-2 M solution of sodium oxalate. Ka1 = 5.62 x 10^-2, Ka2 = 5.42 x 10^-5

Answer 1

For the vast majority of polyprotic acid pH questions, onemust only consider the disassociation of the first proton, thesecond/third/etc protons are much harder to lose and thus theconcentration of H+ from those disassociations are negligible forall practical purposes.

First, we do an ICE table:

1 x 10^-2-x +x +x

Ka1=5.62e-2=(x^2)/( 1 x 10^-2-x)

x^2+5.62e-2*x-5.62e-4=0

Then, solve this quadratic equation, we get x = [H+]= 0.065M

pH = -log[H+] = 1.19