The document discusses electrolysis of aqueous solutions. It explains that aqueous solutions contain anions, cations, and ions from the partial dissociation of water (H+ and OH-). Electrolysis of copper(II) sulfate solution results in copper metal depositing at the cathode and oxygen gas releasing at the anode. Several factors affect the products of electrolysis, including position of ions in the electrochemical series and concentration of electrolytes. The document concludes with an example of the half reactions during electrolysis of copper(II) sulfate solution.

1. Tuesday
18th September 2007
9.00 – 9.35 a.m
SUBTOPIC FOR
TODAY
ELECTROLYSIS OF
AQUEOUS SOLUTIONS

2. ELECTROLYSIS OF AQUEOUS
SOLUTIONS
What you understand about electrolysis
from the previous lesson?

3. Can anyone give an idea what is
aqueous solutions?
Aqueous solution is a solution produced
when the compound is dissolved in water.
It contains:
a. anions and cations of the compound.
b. hydrogen ions, H+ and hydroxide ions,
OH- from the partial dissociation of
water molecules.

4. What is the different between
electrolysis in molten compound
and electrolysis in aqueous
solutions?
 In molten compound it only contain anion
and cation of the compound.
 But in aqueous solution it contain anion,
cation and two types of ions come from
water.

5. Electrolysis of copper (II) sulphate
solution
A
Anode (Carbon) Cathode (Carbon)
H+
H+
SO42-
SO42-
Cu2+ Electrolyte
Cu2+ OH- -
OH (CuSO4)

6. Example: Electrolysis of
Aqueous NaCl
Cations Anions
Na+ Cl-
H+ OH-

7. Experiment 6.3: Electrolysis of
Aqueous Solutions
 The electrolytic cell is filled with 0.1 M copper (II)
sulphate solution until it is half full.
 The apparatus is set up as shown in Figure 6.5.
 The switch is turn on to allow electricity to pass
through the electrolyte for a few minutes.
 What happen in the anode and the cathode is
observed.
 Any gas release is test using a glowing splinter and a
lighted splinter.
 Steps 1 to 5 are repeat using 0.1 M sulphuric acid.
 All observation is recorded.

8. Figure 6.5
Test tube
Electrolyte
Carbon
electrodes
Ammeter
Switch A
Battery

9. Result
Electrolyte Ions present in Observation
electrolyte Anode Cathode
Copper (II) H+, OH-, Cu2+, A gas is An orange
liberated. This coloured
sulphate SO42- gas ignites a deposit is
glowing formed.
splinter.
Sulphuric H+, OH-, SO42- Colourless Colourless
gas is gas is
acid liberated. The liberated. A
glowing pop sound is
splinter burst heard when
into flame the gas is
when it is tested with the
tested with the burning
gas. splinter.

10. ACTIVITY 1

11. Factors Affecting Electrolysis
of an Aqueous Solution

12. Position of the elements in the
electrochemical series.
 For positive ions, the facility of discharge
decrease in going from those least
electropositive to those most
electropositive.
 For example, if both copper and hydrogen
ions are present in solution, it will be the
copper ions which take electrons from the
cathode to become copper atoms.

13. Effect of the electrode on the
product of the electrolysis.

This is not as important as either of the
other two factors, except in certain
cases.
 For example in the electrolysis of molten
sodium chloride using a mercury
cathode, sodium ions are discharged in
preference to hydrogen ions which are
lower in the series.

14. The effects of concentration of
electrolytes.

Irrespective of the position of the ions in the
electrochemical series, there is a tendency to
promote the discharge of the most concentrated ion
present.

For example, in concentrated sodium chloride solution
(i.e. brine) , the two cations present are the chlorine
ion and the hydroxyl ion. Although the hydroxyl ion is
more easily oxidized than the chlorine ion, it is the
chlorine ion which will be discharged because its
concentration is much greater than that of the
hydroxyl ion.

15. Electrochemical Series
Cation Anion
K+ F-
Na2+ SO42-
Easier to discharge
Ca2+ NO3-
Mg2+ Cl-
Al3+ Br-
Zn2+ I-
Fe2+ OH-
Sn2+
Pb2+
H+
Cu2+
Ag+

16.  The reactivity increases down the series.
That is the ions at the bottom of the series
are chosen instead of ions at the higher up
positions.
 In an aqueous solution of an ionic salt, OH -
are usually discharged to form oxygen.

17. Electrolysis of copper (II)
sulphate solution
A
Anode (Carbon) Cathode (Carbon)
H+
H+
SO42-
SO42-
Cu2+ Electrolyte
Cu2+ OH- -
OH (CuSO4)

18. Example
Electrolysis of copper (II) sulphate solution
The ions present in this solution are:
Cu2+, H+, SO42-, OH-.
Half Equation:
at anode: 4OH- (aq) 2H2O(l) + O2 (g) + 4e-
At cathode: Cu2+(aq) + 2e- Cu (s)

19. ACTIVITY 2

20. END OF LESSON