An electrochemical cell is constructed with a piece of copper wire in a 1.00 M solution of Cu(NO3)2 — Electrochemistry Chemistry Question
Problem Context
An electrochemical cell is constructed with a piece of copper wire in a 1.00 M solution of Cu(NO3)2 and a piece of chromium wire in a 1.00 M solution of Cr(NO3)3.
The standard reduction potentials for Cr3+(aq) and Cu2+(aq) are:
Cr3+(aq) + 3e– -⟶ Cr(s) –0.744 V
Cu2+(aq) + 2e– -⟶ Cu(s) 0.340 V
Write a balanced equation for the spontaneous reaction that occurs in this cell and calculate the potential it produces.
Model Answer
2Cr(s) + 3 Cu2+(aq) → 2 Cr3+(aq) + 3 Cu(s)
E o = Eox + Ered = 0.744 + 0.340 = 1.084 V
Sketch a diagram for this cell.
i. Label the anode.
ii. Show the direction of electron flow in the external circuit.
iii. Show the direction of movement of nitrate ions. Explain.
The cell is allowed to operate until the [Cu2+] = 0.10 M.
i. Find the [Cr3+].
Model Answer
[Cu2+] goes from 1.0 M to 0.10 M, so ∆[Cu2+] is –0.90
∆[Cr3+] = 0.90 × 2/3 = 0.60
so, [Cr3+] = 1.60
plug these values into the equation,
ii. Calculate the cell potential at these concentrations.