EPTThis one lab was basically about electrochemical cells. This particular problem involves with the redox reaction:
Cu2+(aq) + Zn -> Zn2+(aq) + Cu
So in the end I'm supposed to calculate the formation constant K of this equation:
Cu2+(aq) + 4 NH3(aq) -> (Cu(NH3)4)2+
The first step is to calculate the concentration of Cu2+ using the nernst equation. The voltage potential recorded from the lab is .414 while the standard was calculated to be 1.781. Note that these values were based on using zinc as the standard electrode. n is equal to 2 because 2 electrons were transferred in the redox reaction.
So using the nernst equation:
.414 = 1.781 - (0.592/2)*log(Q)
Q = 41,500
So using Q I used that with the known concentration of Zn2+ (which is 1.0 M) to finally calculate the concentration of Cu2+.
41500 = 1.0/X
X = .000024 M
So the next step is to calculate the concentration of Cu(NH3)4 2+. In this lab, my teacher told me to assume that since the concentration of NH3 is very high (6.0 M), all the Cu2+ will react to form the Cu(NH3)4 2+. The intial moles before the reaction of Cu2+ was calculated to be .0009 (from before) So...
.0009 moles Cu2+ = .0009 moles Cu(NH3)4 2+
.0009 moles / .109 liters (found beforehand) = .0826 M
So now we can finally calculate the formation constant K knowing that NH3 is 6.0 M and will not change because it is in excess amounts.
K = [Cu(NH3)4 2+]/[Cu2+][NH3]^4
Using the three numbers... K = 2.655
So here's the problem, 2.655 is not even close to the accepted value which is 2x10^13. I'm pretty sure I screwed up something, help me TL.net!
edit: nvm I found the problem.
