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 need to use the Nernst equation:
Ecell = E°cell - (0.05916 V / n) * log(Q)
Where:
- Ecell is the cell potential after the reaction.
- E°cell is the standard cell potential.
- n is the number of electrons transferred in the balanced redox equation.
- Q is the reaction quotient.
Let's break down the problem step by step:
1. Identify the half-reactions:
- Fe3+ + e- -> Fe2+ (cathode reduction half-reaction)
- Pb2+ + 2e- -> Pb (anode oxidation half-reaction)
2. Determine the standard cell potential:
- Look up the standard reduction potentials in a table (values are usually given with respect to the standard hydrogen electrode, SHE).
- The standard reduction potential for Fe3+ to Fe2+ is +0.771 V.
- The standard reduction potential for Pb2+ to Pb is -0.126 V.
- E°cell = E°cathode - E°anode = (+0.771 V) - (-0.126 V)
3. Calculate the reaction quotient (Q):
- Q = (Pb2+)^3 / (Fe3+)^2
- Given the concentrations: [Pb2+] = 1.27 M (increased 3 times) and [Fe3+] = 2.29 M (decreased by 1.432 M).
- Q = (1.27 M)^3 / (2.29 M - 1.432 M)^2
4. Substitute the values into the Nernst equation:
- Ecell = (+0.771 V) - (0.05916 V / 6) * log(Q)
- Calculate log(Q) using the values of Q.
- Plug the values into the equation and solve for Ecell.
Based on the given information, the calculated cell potential should be 0.0794 V. If your calculated value differs, it is possible that there was a mistake in the calculation or rounding errors. Double-check your calculations and make sure to use the correct formula and values consistently throughout the process.