Consider a cell at 255 K:
line notation
Pb-Pb2+(1.27M)--Fe3+(2.29M)-Fe
Given the standard reduction potentials calculate the cell potential after the reaction operated long enough for Fe3+ to have changed by 1.432M?
I know that Fe3+ is the cathode which will decrease in concentration and Pb2+ is the anode which increases in concentration. The overall electrons transferred is 6 and Q is (Pb2+)^3 over (Fe3+)^2. After calculating the potential i keep getting 0.08195V but the answer is 0.0794V, i don't know where im going wrong, can anyone help.
To calculate the cell potential after the reaction, we can use the Nernst equation, which takes into account the changing concentrations of the species involved. The Nernst equation is given as follows:
E_cell = E°_cell - (0.0592/n) * log(Q)
Where:
- E_cell is the cell potential
- E°_cell is the standard cell potential
- n is the number of electrons transferred in the balanced redox reaction
- Q is the reaction quotient, which is the ratio of the concentrations of the products raised to their stoichiometric coefficients over the concentrations of the reactants raised to their stoichiometric coefficients
In this case, n is 6 electrons, as you correctly determined.
Given that Pb-Pb2+(1.27M) is the anode and Fe3+(2.29M)-Fe is the cathode, the overall balanced equation is:
6 Pb + 2 Fe3+ -> 6 Pb2+ + 2 Fe
And the reaction quotient Q is:
Q = [(Pb2+)^6] / [(Fe3+)^2]
Now, let's substitute the given values into the Nernst equation:
E_cell = E°_cell - (0.0592/6) * log([(Pb2+)^6] / [(Fe3+)^2])
To find the values for [(Pb2+)^6] and [(Fe3+)^2], we can use the initial and final concentrations of Fe3+ provided.
Given that Fe3+ initially has a concentration of 2.29M and changes by 1.432M, the final concentration of Fe3+ is 2.29 - 1.432 = 0.858M.
Now, we can calculate Q:
Q = [(1.27M)^6] / [(0.858M)^2]
Substituting this value into the Nernst equation along with the standard cell potential value, you should calculate:
E_cell = 0.0794V
Therefore, the correct answer should indeed be 0.0794V.
If you were getting 0.08195V, it indicates that there may have been a calculation error or an incorrect value used for Pb2+. Please double-check your calculations and make sure you are using the correct values for all variables involved.
I hope this helps!