1.57    calculate the amounts of the products of the electrolysis of molten salts and aqueous solutions.

You may have to work out how much charge has flowed using the relationship Q = It

(Q = charge in Coulombs, I = current in Amps and t = time in seconds)

Convert Coulombs to moles of electrons with the Faraday Constant

Use mole ratios from the equations to work out the number of moles of product formed.

e.g.      in the electrolysis of molten sodium chloride, 0.5 A flows for 15 minutes. What mass of sodium is made, and what volume of chlorine gas?

            Q= It     = 0.5 A x (15 x 60) s      = 450 C

Moles of electrons         = Q ÷ Faraday Constant

= 450 ÷  96500

= 0.00466 mol

Na+ + e- → Na (so one mole of e- produces one mole of Na)

Moles of Na      = 0.00466 mol

Mass of Na       = moles × A_r

=  0.00466 ×  23   =   0.11 g

2Cl-(aq) ® Cl2(g)  + 2e-  (so two moles of e- for one mole of Cl2)

Moles of Cl2        = 0.00466 ÷  2 = 0.00233 mol

Volume of Cl2     = moles ×  molar volume

            = 0.00233 ×  24000   =   56 cm3