Faraday's Constant

You may find the section on current in the physics tutorial helpful.

Redox reactions have many important uses. One of these is electrolysis, the conversion of electrical energy to chemical energy.
Do you remember this table? (From the electrodes segment)

Anode	Oxidation
Cathode	Reduction

In electrolysis, oxidation still occurs at the anode, and reduction still occurs at the cathode, but the polarity of the electrodes is different.

Cells	Anode	Oxidation	-
	Cathode	Reduction	+
Electrolysis	Anode	Oxidation	+
	Cathode	Reduction	-

Keep this in mind as we go.

Faraday's constant is the charge carried by one mole of electrons. There are 6.02214e23 electrons per mole of electrons. (Avogadro's number)
Each electron has a charge of 1.602177e-19 coulombs per electron.
So Faraday's constant is 1.602177e-19 coulombs per electron * 6.02214e23 electrons per mole of electrons = 9.64853e4 coulombs / mole of electrons.
This constant is useful to us when we are doing problems in electrolysis.

Let's work a problem.
A current of .01 amperes is passed through a solution of AgNo₃ for eight hours.
What mass of silver accumulates on the cathode?

1. First we convert our time into seconds, 8 hours is equal to 480 minutes is equal to 28,800 seconds.
2. Next we find the charge transferred. We know the current is .01A or .01 coulombs/sec, which means that over 28800 seconds we have 288 coulombs of electrons.
3. Checking our table of standard reduction potentials, we confirm that there is only one electron transferred per silver atom.
4. We divide 288 coulombs by Faraday's constant, 9.64853e4 coulombs a mole to obtain the moles of silver atoms, .002985 moles
5. We use a periodic table to find the atomic mass of silver, about 107.8682 grams per mole.
6. Finally we find the mass of the deposited silver, 107.8682 grams per mole * .002985 moles = .322 grams of silver.