Question

how many grams of chromium will be obtained when an aqueous Cr₂(SO₄)₃(aq) solution is electrolyzed for 15.00 min with a constant current of 2.40A? (molar mass of chromium 52g/mol)

Answer 1

First we have to estimate the amount of charges flow through the solution. It can be estimated from the following equation

Q= I*t where Q is the charge, I is current is amperes (A) and t is time is second

In this case, Q = 2.40*15*60 Coulomb = 2160 C

We know 1 Faraday current yields 1 mol electron/charge. 1 F = 96500 C. So 2160 C will yield 2160/96500 = 0.0224 mol e

Now Cr has 3+ charge is the compound. So reduction of Cr is a three electron process. So 1 mol e will yield 1/3 mol Cr from the compound. So 0.0224 mol e^- will yiled 0.0224/3 = 0.0075 mol Cr.

Molecular weight of Cr is 52g/mol. So 0.0075 mol Cr means 0.0075*52 = 0.39 g chromium.

So the amount of chromium obtained will be 0.39g.