Faraday's law describes the amount of reduction that occurs in an electrolytic cell. Occasionally, calculations involving current and accumulated product are required. Current is measured in charge per unit time. Since the mass of the product can be converted to moles, it is helpful to be able to convert charge to moles as well. Faraday's constant F is the required conversion factor. To calculate the charge on one mole of electrons, the number of electrons (Avogadro's number) is multiplied by the unit charge ( /electron), which is the magnitude of the charge present on an electron. The result is Faraday's constant 96485C/mol.
Example:
A 5A current is passed through a solution containing manganese ions for 4 hours. If 5.87g of solid manganese has accumulated at the end of this time, what was the
original oxidation state of the manganese?
Thinking through the process of conversion is helpful in this problem. The problem gives the rate of charge deposited (amps are Coulombs per second) and the length of time over which charge is deposited. The total charge deposited can then be found. Faraday's constant can be used to convert the charge to moles of electrons. In addition, the grams of product can be converted to moles of product. The moles of electrons and moles of product can then be compared to determine how many moles of
