something strange. i made an electrochemistry experiment in which i have measured the potential of cell: Ag, AgCl | (1M)KCl ║ [Fe(CN)6] 3-, [Fe(CN)6] 4- | Pt
with different concentrations of Fe+2/Fe+3 .
from the results i have found the faraday constant:
96181 Coulon /mol
very close to the published value (99.7% accuracy).
the intercept of the graph of E (v) against ln(Fe+2/Fe+3) is:
intercept: 0.198985714 V
(the intercept is also the standard potential for the cell)
yet, when i tried to find the standard potential of
Fe3+ +e- -> Fe2+
i got the result of +0.423 V which is almost half of the published value (+0.77 V)
E_cathode =E^° + E_anode E_cathode=0.198985+0.224= +0.423 V
how can it be that the faraday constant is almost accurate and in the same time the result of the standard potential is far from the real one.? i'm sure i don't have any calculation mistakes, if it's necessary i can describe the method of work here.