2. Electrolysis
Process of decomposing certain liquids and
solutions into their component parts by the
passage of electricity through them.
3. Faraday’s laws of electrolysis
1. The mass of a given element liberated
during the process of electrolysis is directly
proportional to the quantity of electricity Q
that is passed through it
m α Q m = Z I t
Z is the electrochemical equivalent: mass liberated by
passage of 1C of electricity
4. Faraday’s laws of electrolysis
2) The relative masses of substances or the
number of moles of different elements
liberated by the same quantity of electricity
is proportional to their chemical equivalent
C
m1/m2 = c1/c2
What is Faraday’s constant F? = Qty of
charge required to dissolve one mole of
singly charged ion
5. EG
What amount of current is required to
deposit 18.0 g of silver during electrolysis by
passing the current steadily for 500
minutes?
Take electrochemical equivalent of silver to be
0.0012gC-1
6. m = Z I t
18x10-3 = 0.0012 x 10-3 x I x (500 x 60)
18x10-3 = 36 x 10 -3 I
I = 0.5A or 500mA
7. Eg 2
A charge of 1C liberates 0.0033g of copper
during electrolysis. How long will it take a
current of 1A to liberate 0.99g of Cu in the
same process?
8. Solution to EG 2
Remember z = mass liberated by passage of
1C of electricity
Z = 0.0033gC-1
m = ZIt
t = m/ZI = 0.99 x 10-3
0.003 x 10-3 x 1
= 300s or 5 mins.
9. Eg 3
Calculate the quantity of electricity
(coulombs) required to deposit 100.00g of
copper from a CuSO4 solution.
Take: molar mass of Cu = 63.5g/mol
1mol of electron = 96,485.309C
10. Solution to eg 3
1) Determine moles of Cu given out
= 100g divided by molar mass of Cu
=> 100/63.5 = 1.57mol
2) Determine moles of electrons required
Cu2+ + 2e- Cu
Therefore, every mole of Cu given out requires
2 moles of electrons
= 1.57 x 2 = 3.14 mol e- required
3) Convert moles of electrons to Coulombs
=3.14 x 96,485.309 = 3.03 x 105 C
