CHEMISTRY · Multi-part · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry
Problem
During the electrolytic refining of copper, the cathode mass increases while oxygen gas is simultaneously evolved at the anode. In one trial, the cathode gains 56.0 g of Cu(s), and 19.2 g of O2(g) is collected at 25 °C and 1 atm. The process lasts exactly 3.25 h.
Relevant half-reactions:
Cu2+ + 2 e− → Cu(s)
2 H2O(l) → O2(g) + 4 H+ + 4 e−
Molar masses: Cu = 63.55 g mol−1; O2 = 32.00 g mol−1
Faraday constant: F=9.6485×104 C mol−1
(a) Using the observed mass change at the cathode, calculate the number of moles of electrons that enter the cathode during the trial.
(b) Based on the mass of O2 collected, determine the number of moles of electrons released at the anode.
(c) Evaluate whether the electron counts from parts (a) and (b) are stoichiometrically consistent with the listed half-reactions. Provide a quantitative justification for your answer.
(d) Assuming the larger of the two electron counts from parts (a) and (b) represents the total charge that actually flowed through the external circuit, calculate the average current sustained during the 3.25 h run.
(e) If subsequent analysis shows the cathode deposition efficiency was only 92.0 %, determine the theoretical mass of Cu(s) that should have been gained under ideal (100 %) efficiency.