Chapter 6 Electrochemistry

1. Chapter 6
Electrochemistry

2. A. Electrolytes & Non-electrolytes
Electrolytes
Substances that can conduct electricity and
undergo chemical changes
Non-electrolytes
Substances that cannot conduct electricity

3. Electrolyte
Non-electrolyte

4. Why electrolyte at molten and aqueous state
can conduct electricity?
BECAUSE
There presence of free moving ions in the
electrolyte

5. B. Electrolysis of Molten Compounds
Electrolysis
A process where compounds in molten or
aqueous state are broken down into their
constituent elements by passing electricity
through them

6. Electrolytic cell
The set of apparatus needed to conduct
electrolysis
Electrolyte
CathodeAnode
+ -
STEPS OCCUR DURING
ELECTROLYSIS
 Movement of ions to the
electrodes.
 Discharges of ions at the
electrodes.
Graphite or platinum
is usually used as
electrodes because
they are inert.

7. Important note: Observation
Anode (positive electrode)
Electrolysis product Observation Confirmatory test
Chlorine gas Greenish-yellow gas
bubbles released
Place moist blue litmus
paper into test tube
Moist blue litmus paper
turn redBromine gas Brown gas released
Iodine Purple gas released
Oxygen gas Colourless gas bubble
released
Place a glow wooden
splinter near the mouth
of test tube
The glowing wooden
splinter light up
Metal (all metal) The mass of electrode decreased
Copper metal Brown solid formed

8. Important note: Observation
Cathode (negative electrode)
Electrolysis product Observation Confirmatory test
Almost all metal
(except copper metal)
Grey solid formed
The mass of electrode
increase
No test for metals
Copper metal Brown solid formed
Hydrogen gas Colourless gas bubbles
released
Place a lighted wooden
splinter near the mouth
of test tube
A “pop” sound
heard/produced

9. Electrolysis of molten compound

10. Electrolysis of molten compound
• PbBr2
• LiCl
• MgBr2
• PbI2
• ZnO
• CuCl2
• Molten Potassium oxide
• Molten Magnesium oxide
• Molten Potassium iodide

11. Electrolysis of Aqueous Solutions
Factors that affect the electrolysis of an
aqueous solution
• Position of ions in the Electrochemical
Series
• Concentration of ions in the electrolytes
• Types of electrodes used in the electrolysis

12. Position of ions in
the Electrochemical Series
• The ions that are lower in the electrochemical
series will be selected discharged

13. K+
Na+
Ca2+
Mg2+
Al3+
Zn2+
Fe2+
Sn2+
Pb2+
H+
Cu2+
Ag+
F-
SO4
2-
NO3
-
Cl-
Br-
I-
OH-
The Electrochemical Series
Ease of discharge
increases

14. 0.01 mol dm-3 of copper(II) sulphate
using carbon as electrodes
1 mol dm-3 of
copper(II) sulphate
solution
CarbonCarbon

16. Concentration of ions
• If the concentration of a particular ions is
high, the ions is selectively discharged
TIPS:
ANODE
Ion selectively discharged based on CONCENTRATION of
ions
CATHODE
Ion selectively discharged based on position of ions in
Electrochemical Series

17. 2 mol dm-3 of hydrochloric acid, HCl
using platinum as electrodes
2 mol dm-3 of
hydrochloric acid, HCl
PlatinumPlatinum

18. Anode :
Cathode :

19. Types of electrodes
• Electrolysis of copper(II) sulphate, CuSO4
solution using copper electrode
• Electrolysis of silver nitrate, AgNO3 solution
using silver electrode

20. 0.02 mol dm-3 of copper(II) sulphate, CuSO4
using copper as electrodes
0.02 mol dm-3 of
copper(II) sulphate,
CuSO4
CopperCopper

21. Anode :
Cathode :

22. 0.02 mol dm-3 of silver nitrate, AgNO3
using silver as electrodes
0.02 mol dm-3 of silver
nitrate, AgNO3
SilverSilver

23. D. Electrolysis in Industries
• The most industrial application of electrolysis:
1. extraction
2. purification
3. electroplating of metals

24. E. Voltaic Cells
• Chemical energy to electrical energy
• Examples of chemical cell:
 simple voltaic cell
 Daniell cell
 dry cell
 alkaline cell
 lead-acid accumulator

25. Simple Voltaic Cell
Two different metals being immersed into an
electrolyte and connected by wire
V

26. Daniell cell – has two types
• Use porous pot
• Use salt bridge

27. Use porous pot

28. Use salt bridge

29. F. The Electrochemical Series
• The Electrochemical Series is series of
element, arranged according to the order of
decreasing tendency to released electrons.
• Or the greater the tendency to donate
electrons, the more electropositive is the
metal and the higher it is in the
Electrochemical Series.

30. Principles Used:
• Metals are arranged according to the tendency of
their atoms to release electron.
• More the tendency of their atoms to release
electron, the higher located it is in the series.
• Elements located at HIGHER part of the
Electrochemical Series are more electropositive
and have higher tendencies to release electrons
to form positive ions.
• Example : magnesium is more electropositive
than copper in Electrochemical Series

31. The Electrochemical Series can be
constructed based on:
Metals are arranged according to their tendency
to release electrons to form positive ion (cation).
• metal has a higher tendency to release
electron placed a the higher position in
Electrochemical Series.
• the metal act as negative terminal

32. The ability of a metal to displace another metal
from its salt solution.
• If metal is able to displace another metal
from its salt solution, this metal is placed
at the higher position in Electrochemical
Series

33. The potential difference between two metals.
• The further apart between two metals in
the Electrochemical Series, the greater the
potential difference between them.
• The greater the voltage produced by the
cell.