Question

Oxalic acid , HOOCCOOH (aq) , is a diprotic acid with Ka1= 0.0560 and Ka2=0.0145. Determine the [-OOCCOO-] in a solution with an initial concentration of 0.139 M oxalic acid.

HOOCCOOH(aq) = HOOCCOO-(aq) + H+(aq)
HOOCCOO-(aq) = -OOCCOO-(aq) + H+(aq)

I have tried a ICE diagram:

HOOCCOO^- <=> ^-OOCCOO^-+ H^+
I: 0......0.139......0
C: -X......+X.......+X
E: -X......0.139+x......X

K= 0.139+X *X / -X
0.0145 = 0.139+X *X /-X
X= 0.03823
[-OOCCOO-] = 0.139-.03823= 0.10077

Not sure where I went wrong. Please help

Amanda

Answer 1

Where did you get these Ka values. The literature gives values that are about 1000 between k1 and k2 but your values have a ratio of about 4 and not 1000.

Answer 2

the Ka values are given in the question from the homework.

Ka1 = 0.0560, for the equation: HOOCCOOH(aq) = HOOCCOO-(aq) + H+(aq)

While Ka2 = 0.0145, for the equation:
HOOCCOO-(aq) = -OOCCOO-(aq) + H+(aq)