Electrochemistry Regarding Electrolysis

Question

How long must a 15.0 A current flow through a solution of zinc sulfate (ZnSO₄) in order to form 16.3 g of Zn solid?

Answer 1

Hi Tasha!

Electrochemistry can be tricky, but let's see if I can help you out a bit.

So we need to find out how long it will take to form 16.3 g of Zn solid. The good news is that we can use dimensional analysis to get to our answer. Conceptually, our plan will look like this:

g Zn solid → mol Zn → mol e^- → Coulombs → sec → minutes

To go from grams of zinc into moles of zinc, we will use zinc's molar mass (65.38 g/mol)

Using the half-reaction of Zn solid to its ionic state of Zn²⁺, we can find the number of moles of electrons.

Zn → Zn²⁺ + 2e^-

We can then use Faraday's constant to calculate Coulombs.

Since current is a measure of charge per unit time, we can use the given current to find the amount of time in seconds (1 A = 1 C/s). If your answer needs to be in minutes, a simple unit conversion from seconds to minutes can be used.

So all in all, this is what the overall process should look like.

16.3 g Zn x (1 mol Zn/65.38 g Zn) x (2 mol e^-/1mol Zn) x (96,485 C/1 mol e^-) x (1 sec/15.0 C) x (1 min/60 sec) = 53.5 min

Please reach out if you need any further explanation!

Best,

Bradley