In galvanization, a protective zinc coating is applied to steel or iron. The pro

Question

In galvanization, a protective zinc coating is applied to steel or iron. The process for making the molten zinc used for galvanization is complex, but we will consider a simplified version for this problem: In order to prepare the zinc metal for galvanization, electrolysis is performed on an aqueous znSO_4 solution, causing zinc meta to deposit at the cathode and oxygen to form at the anode. What is the minimum voltage required to drive this reaction under standard conditions? If you wish to produce 1.0 kg of zinc metal from an aqueous ZnSO_4 solution, how long would you need to run a cell with a current of 3,000 A?

Explanation / Answer

cathode reaction:-

Zn2+(aq) + 2e- -----> Zn(s) ; E0 = -0.763 V

Anode reaction:-

2H2O(l) -----> O2(g) + 4e- + 4H+; E0 = -1.229 V

Overall reaction :-

2Zn2+(aq) + 2H2O(l) -----> O2(g) + 2Zn(s) + 4H+(aq) ; E0cell = -0.763- (-1.229) = 0.466 V

2) Equivalent mass of Zn in ZnSO4 = molar mass/2 = 65.38/2 = 32.69 g

Now, equivalents of Zn in 1000 g of it = mass/equivalent mass = 1000/32.69 = 30.59

Now, Total charge required = number of equivalents*Faraday's constant = 30.59*96500 = 2951973.08 C

Thus, time = charge/current = 2951973.08/3000 = 984 sec = 16.4 minutes.

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