The following electrochemical cell can be used to calculate the formation constant Kf for a metal and EDTA. The cell has a voltage of -0.262V. The right half cell contains a metal (M^2+) with a standard reduction potential of -0.236V. Calculate the Kf for the metal EDTA complex.

Question

The following electrochemical cell can be used to calculate the formation constant Kf for a metal and EDTA.  The cell has a voltage of -0.262V.  The right half cell contains a metal (M^2+) with a standard reduction potential of -0.236V.  Calculate the Kf for the metal EDTA complex.  
Citric acid=Pka3=6.396
Anode:
PH2bar=0.40
30mL of 0.010M citric acid
70.0mL of 0.010 NaOH M
Cathode:
30.0mL of 0.010 M M^2+
70.0mL of 0.010M EDTA
alphaY4-=0.81 at pH 11.00
I am trying to get the [H+] concentration first.  Then plug into equation...  I keep getting 1.99E-07 but not sure if it's right... I think I can do the math from there..
Thanks,

DrBob222 · Accepted Answer

I think the pH comes from the reaction of citric acid with NaOH. That is a buffer.
...........H3C + NaOH ==> NaH2C + H2O
I..........0.3...0..........0
add..............0.7...........
C.........-0.3..-0.3.........0.3
E...........0.....0.4........0.3
pH = pKa3 + log (base)/(acid)
pH = 6.396 + log (0.3/0.4) = 6.27 in the anode. Of course the cathode pH is 11.00