C1.1b Electrolysis 1st year college presentation

Electrolysis

1. By: Engr. Hazel Mei M. Manuel, RChT

2. A process where electricityis used to separate
chemical compounds.
Direct current is passed through the compound.
(The compound can be in moltenor aqueous state)
Electrical energy (from the direct current) is changed
into chemical energy (the decomposition of compound)

3. TWO ELECTRODES
ELECTROLYTE
DIRECT CURRENT (DC) supply

4. ELECTROLYTE –substance which conduct electricity
-contains free ions, which are the carriers of electric
current

5. DIRECT CURRENT (DC) supply –provides the energy necessary to create
or discharge the ions in the electrolyte

6. TWO ELECTRODES –electrical conductor that provides the
physical interface between the electrical circuit providing
the energy and the electrolyte.

7. EXAMPLES
NaCl→Na + Cl
2
sodium chloride sodium chloride
H
2O→H
2+ O
2
Water hydrogen oxygen

8. Electrolysis of Sodium Chloride (NaCl)
NaCl →Na + Cl
2
+1 -1 0 0
Oxidation Number (O.N.):
Element by itself: 0
Group 1A: +1
Group 2A: +2
Halogens: -1
Hydrogen: +1 (with non-metals)
-1 (with metals)
0xygen: -2
-1 (in peroxide)
Gain of Electrons = Reduction (O.N.↓)
Loss of Electrons = Oxidation (O.N.↑)
Na is reduced
(it gainse-)
Clis oxidized
(It losese-)
This process is NOT Spontaneous
-It doesn’t happen on its own.

9. Electrolysis of Sodium Chloride (NaCl)
NaCl →Na + Cl
2
+1 -1 0 0
The electrical energy from a
batterycan FORCE this process
to happen.
Positive Side (+)
-PullsElectrons in
Negative Side (-)
-Pushes Electrons out
e- e-
Pulls e-from Cl,
Oxidizing it
Push e-to sodium,
Reducing it
BATTERY
Cl
-1
Na
+1

10. ElectorlyticCell
Oxidation Reduction
(+) (-)
Cl
e--1
e-
e-
Na
e-
+1

11. Half Reactions
Na
+
+ e-→Na
2Cl
-
→Cl
2+ 2e-
Reduction:
Oxidation:

12. Combine the Half Reactions
Na
+
+ e-→Na
2Cl
-
→Cl
2+ 2e-
Reduction:
Oxidation:
2Na
+
+ 2e-→2Na
2Na
+
+ 2Cl
-
→2Na + Cl
2
2NaCl
(l)→Na
(l)+ Cl
2(g)
( ) x 2

13. Electrolysis of Water (H
20)
2H
20→2H
2+ O
2
+1 -2 0 0
Oxidation Number (O.N.):
Element by itself: 0
Group 1A: +1
Group 2A: +2
Halogens: -1
Hydrogen: +1 (with non-metals)
-1 (with metals)
0xygen: -2
-1 (in peroxide)
Gain of Electrons = Reduction (O.N.↓)
Loss of Electrons = Oxidation (O.N.↑)
Oxygen is oxidized
(It losese-)
Hydrogen is reduced
(It gainse-)

14. Half Reactions
Reduction of Hydrogen:
Oxidation of Oxygen:
2H
20 + 2e-→H
2+ 2OH
-
2H
20 →O
2+ 4H
+
+ 4e-

15. Reduction :
Oxidation :
2H
20 + 2e-→H
2+ 2OH
-
2H
20 →O
2+ 4H
+
+ 4e-
Combine the Half Reactions
6H
20 →2H
2+ 4H
20 + O
2
4H
20 + 4e-→2H
2+ 4OH
-
2H
20
(l)→2H
2(g)+ O
2(g)
( ) x 2