electrolysis

1. LESSON 9
ELECTROLYSIS PART 2

2. A. POSITION IN THE
ELECTROCHEMICAL
SERIES

3. ELECTROCHEMICAL SERIES
The lower position of the ion in
the Electrochemical Series,
the easier the ion to be
discharged during electrolysis
Panic=positive anode, negative cathode

4. ELECTROLYSIS OF AQUEOUS COPPER SULPHATE SOLUTION
anode:
4OH- (aq) → 2H2O(l) + O2 (g) + 4e-
cathode:
Cu2+ (aq) +2e- →Cu (s)
➤ OH- are selectively discharged
➤ Oxygen gas are released
➤ Cu2+are selectively discharged
➤ Copper metal deposited on cathode
ions: Cu2+, H+, SO42-, OH-
With carbon electrodes

5. ➤ Blue solution fades
➤ Color get less intense with time
ELECTROLYSIS OF AQUEOUS COPPER SULPHATE SOLUTION

6. B. CONCENTRATION
OF IONS

7. ELECTROLYSIS OF DILUTE SODIUM CHLORIDE SOLUTION
anode:
4OH- (aq) → 2H2O(l) + O2 (g) + 4e-
cathode:
2H+ (aq) +2e- →H2 (g)
➤ H+ are selectively discharged
➤ Hydrogen gas are released
➤ OH- are selectively discharged
➤ Oxygen gas released

8. ELECTROLYSIS OF CONCENTRATED SODIUM CHLORIDE (BRINE) 4.58 MIN
➤ H+ are selectively discharged
➤ Hydrogen gas are released
➤ Cl- are found in higher concentration
➤ Chlorine gas released
anode:
2Cl- (aq) → Cl2(g) + 2e-
cathode:
2H+ (aq) +2e- →H2 (g)
ions: Cl-, OH-, Na+, H+

9. C. NATURE OF
ELECTRODE

10. Electrodes
Inert
Graphite
Platinum
Reactive
Copper
Silver

11. NATURE OF ELECTRODES
Inert
➤ Non corrosive
➤ Do not affect the discharge of ions in any way
Reactive
➤ Will interfere with order of discharge of ions in the electrolyte

12. ELECTROLYSIS OF AQUEOUS COPPER SULPHATE SOLUTION
With copper electrodes
➤ Same effect/result as purifying copper
➤ Cathode increases in size
➤ Anode decreases in size
➤ Color intensity of blue solution remains the same
Reduction
cathode:
2Cu2+ (aq) + 2e-→ Cu(s)
Oxidation
anode:
Cu( s ) →Cu2+ (aq) + 2e-

13. ELECTROPLATING

14. ELECTROPLATING 1.21-4.08 MIN
Plating metal Object to be plated
Examples of plating metals are nickel, zinc, copper, silver, gold
Oxidation
Anode :
Ag (s) → Ag+ (aq) + e-
Reduction
Cathode :
Ag+ (aq) + e- →Ag (s)

15. PURIFYING
OF COPPER

16. PURIFYING COPPER 4.32 MIN
➤ Concentration of electrolyte remains constant
➤ Colour intensity remains the same
➤ Rate of cu2+ ions released at anode = rate of cu2+ discharged at cathode
➤ Impurities deposited below anode eg. gold, silver, platinum
Reduction
cathode:
2Cu2+ (aq) + 2e-→ Cu(s)
Oxidation
anode:
Cu( s ) →Cu2+ (aq) + 2e-

17. SIMPLE CELL

18. SIMPLE CELL
➤ Electron flow from the more reactive metal to the less reactive metal
➤ Reactive metal undergoes oxidation
➤ Less reactive metal undergoes reduction

19. 2 metals of different reactivity
➤ The greater the difference in reactivity, the greater the voltage, the greater the
electrical energy produced

20. DANIELL CELL (SIMPLE CELL DIPPED IN TWO ELECTROLYTES)
➤ The 2 electrolytes are connected by a salt bridge
➤ Salt bridge contains salts or inert ions like sodium nitrate or dilute H2SO4 that
doesn’t react with the electrolyte
➤ Zinc more reactive than copper
➤ Electrons flow from zinc to copper
Oxidation:
-Zinc loses electron
-becomes negative terminal
Reduction :
-Copper gains electron
-becomes positive terminal
Cu2+ (aq) + 2e-→ Cu (s) Zn (s) → Zn (aq) + 2e-