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
See your post above.
To determine the concentration of [-OOCCOO-] in the solution, you need to consider the ionization reactions of oxalic acid and the equilibrium expressions associated with each dissociation step.
The ionization reactions are as follows:
HOOCCOOH(aq) ⇌ HOOCCOO-(aq) + H+(aq) (equation 1)
HOOCCOO-(aq) ⇌ -OOCCOO-(aq) + H+(aq) (equation 2)
Given the equilibrium constants Ka1 and Ka2 for equations 1 and 2, we have:
Ka1 = [HOOCCOO-][H+]/[HOOCCOOH] (equation 3)
Ka2 = [-OOCCOO-][H+]/[HOOCCOO-] (equation 4)
You are given the initial concentration of oxalic acid, [HOOCCOOH] = 0.139 M.
First, let's find the concentration of [H+] at equilibrium for equation 1.
Using the ICE table for equation 1:
I: 0 0.139 0
C: -x +x +x
E: -x 0.139+x x
Substituting these values into equation 3:
0.0560 = (x)(x)/(0.139-x)
We neglect the +x term in the denominator, so:
0.0560 = x^2/0.139
Solving for x, we find x = 0.0587 M, which represents the concentration of [H+] at equilibrium.
Next, let's use this concentration of [H+] to find the concentration of [HOOCCOO-] at equilibrium using equation 2.
Using the ICE table for equation 2:
I: 0 0 0
C: -x +x +x
E: -x x x
Substituting these values into equation 4:
0.0145 = (x)(x)/(-x)
Simplifying the equation:
0.0145 = x
So, we find that the concentration of [HOOCCOO-] at equilibrium is x = 0.0145 M.
Finally, to determine the concentration of [-OOCCOO-], we subtract the concentration of [HOOCCOO-] at equilibrium from the initial concentration of oxalic acid:
[-OOCCOO-] = [HOOCCOO-] at equilibrium = 0.0145 M.
Therefore, the concentration of [-OOCCOO-] in the solution is 0.0145 M.