3 Cu+(aq) + Au3+(aq) → 3 Cu2+(aq) + Au(s) A student studying the reaction represented above construc — Electrochemistry Chemistry Question
Problem Context
3 Cu+(aq) + Au3+(aq) → 3 Cu2+(aq) + Au(s)
A student studying the reaction represented above constructs a voltaic cell as shown in the diagram below.
[VISUAL]
The cell contains an Au(s) electrode in a beaker containing 1.00 M Au(NO3)3(aq) and a Pt(s) electrode in a beaker containing 1.00 M CuNO3(aq) and 1.00 M Cu(NO3)2(aq).
The standard reduction potentials associated with the cell are given in the following table.
| Half-reaction | E° (V) |
|---|---|
| Cu2+(aq) + e− → Cu+(aq) | 0.16 |
| Au3+(aq) + 3 e− → Au(s) | 1.50 |
Model Answer
E° = 1.50 V – 0.16 V = 1.34 V
1 point is earned for the correct answer.
Model Answer
The mass of the Pt(s) electrode remains the same because the Pt does not react and no Cu atoms will be deposited on the Pt electrode.
1 point is earned for the correct answer and a valid justification.
Model Answer
In a redox reaction, the number of electrons lost must equal the number gained, so the net charge must be zero. The total charge of the cations is less than the total charge of the anions.
1 point is earned for a valid explanation.
Model Answer
0.185 g Au × (1 mol Au / 196.97 g Au) = 9.39 × 10^−4 mol Au
1 point is earned for the correct calculation of the number of moles. || I = q / t
q = 9.39 × 10^−4 mol Au × (3 mol e− / 1 mol Au) × 96,485 C/mol e−
t = 30.0 min × (60 sec / 1 min)
I = [9.39 × 10^−4 mol Au × 3 × 96,485 C/mol e−] / [30.0 × 60 s] = 0.151 C/s = 0.151 A
1 point is earned for the correct number of electrons transferred (may be implicit).
1 point is earned for the correct calculation of the current.
Model Answer
For CuCl: CuCl(s) ⇄ Cu+(aq) + Cl−(aq)
Ksp = [Cu+][Cl−]
1.7 × 10^−7 = x^2
x = 4.1 × 10^−4 M = solubility of CuCl
CuCl has a lower solubility compared to CuCl2 and will precipitate first.
1 point is earned for a correct calculation of the solubility of CuCl.
1 point is earned for identifying the precipitate with the lower solubility.
Model Answer
Cu+(aq) + Cl−(aq) → CuCl(s)
1 point is earned for the equation consistent with the answer to part (e).
Model Answer
Disagree.
The precipitate will decrease [Cu+], which will cause Q to increase and become closer to the value of K. Therefore, the voltage of the cell will decrease.
1 point is earned for a correct choice and a valid justification.