ICS

Electrolysis

• non-spontaneous reaction is caused by the passage of an electric current through a solution

ICS

ICS

Electrolysis

Electrolysis of Sodium chloride

(chlor-alkali process)

molten reactants => liquid sodium and chlorine gas

aqueous reactants => caustic soda (sodium hydroxide) and chlorine gas

ICS

Electrolysis

Preparation of Aluminum (Hall process)

ICS

Electrolytic Refining of Copper

Cu(s) + Cu+2(aq) --> Cu+2

(aq) + Cu(s)

impure pure anode cathode

impurities: anode mud; Ag, Au, Pb

ICS

ICS

Quantitative Aspects of Electrolysis

• 1 coulomb = 1 amp sec

• 1 mole e- = 96,500 coulombs

ICS

Electroplating

EXAMPLE: How many grams of chromium can be plated from a Cr+6 solution in 45 minutes at a 25 amp current?

ICS

Electroplating

EXAMPLE: How many grams of chromium can be plated from a Cr+6 solution in 45 minutes at a 25 amp current?

(45 min)#g Cr = ------------

ICS

Electroplating

EXAMPLE: How many grams of chromium can be plated from a Cr+6 solution in 45 minutes at a 25 amp current?

definition of minute

(45 min)(60 sec)#g Cr = ---------------------

(1 min)

ICS

Electroplating

EXAMPLE: How many grams of chromium can be plated from a Cr+6 solution in 45 minutes at a 25 amp current?

(45) (60 sec) (25 amp)#g Cr = ---------------------------

(1)

ICS

Electroplating

EXAMPLE: How many grams of chromium can be plated from a Cr+6 solution in 45 minutes at a 25 amp current?

definition of a coulomb

(45)(60 sec)(25 amp)(1 C)#g Cr = -----------------------------

(1) (1 amp sec)

ICS

Electroplating

EXAMPLE: How many grams of chromium can be plated from a Cr+6 solution in 45 minutes at a 25 amp current?

Faraday’s constant

(45)(25)(60)(1 C)(1 mol e-)#g Cr = ----------------------------------

(1)(1)(96,500 C)

ICS

Electroplating

EXAMPLE: How many grams of chromium can be plated from a Cr+6 solution in 45 minutes at a 25 amp current?

atomic weight

(45)(60)(25)(1)(1 mol e-)(52 g Cr)#g Cr = -------------------------------------------

(1)(1)(96,500) (6 mol e-)

ICS

Electroplating

EXAMPLE: How many grams of chromium can be plated from a Cr+6 solution in 45 minutes at a 25 amp current?

(45)(60)(25)(1)(1 mol e-)(52 g Cr)#g Cr = -------------------------------------------

(1)(1)(96,500)(6 mol e-)

= 58 g Cr

ICS

ICS

Corrosion

O2(g) + 4 H+(aq) + 4 e- -----> 2 H2O(l)

Eo = 1.23 V

RustingFe(s) -----> Fe+2

(aq) + 2 e- Eo = 0.44 V

O2(g) + 4 H+(aq) + 4 e- -----> 2 H2O(l) Eo = 1.23 V

------------------------------------------- --------------2 Fe(s) + O2(g) + 4 H+

(aq) ----->

2 H2O(l) + Fe+2(aq) Eo = 1.67 V

ICS

Preventing Corrosion

painting

galvanizing

sacrificial anode