1. C3.4 – Electrolysis and cells
Learning Objectives:
To describe the properties of metals
To explain the processes involved in electrolysis
To describe the principle behind a dry cell

2. Name all the properties of metals that you can

3. catalysts density ductile heat
high properties transition
Iron and copper are both __________ metals. They have __________ melting points, they are good conductors of __________ and electricity and they have a high __________. Transition metals have uses linked to their __________. For example, copper is __________ and so is used to make wires. Some transition metals are used as __________ , speeding up chemical reactions.

4. SPLITTING UP IONIC COMPOUNDS 1
Cl- ION
Na+ ION
Ionic compounds (eg sodium chloride) are made from:
POSTIVE IONS (atoms which LOST negative electrons)
NEGATIVE IONS (atoms which GAINED negative electrons)
As these ions have OPPOSITE CHARGES they attract each other strongly to form IONIC BONDS

5. - - MELT - DISSOLVE 800°C 20°C SPLITTING UP IONIC COMPOUNDS
To make ions move: - + + -
MELT + -
DISSOLVE
H2O
800°C
20°C

6. _ + SEPARATING THE IONS 1 Metal ELECTRODE ELECTRON
Battery pulls electrons off one electrode and pushes them onto the other
This IS SHORT OF electrons so becomes POSITIVELY CHARGED
“ANODE”
This HAS EXTRA electrons so becomes NEGATIVELY CHARGED
“CATHODE”

7. Define the terms:
Electrolyte
Electrode
Anode
Cathode
Inert

8. Electrolysis Practical
Select one of the test substances and connect it into the circuit.
Switch on the power supply. Does the bulb light?
Look carefully for any signs of reaction. These might include:
gases being given off
changes taking place on the surface of the electrodes
changes taking place in the liquid.

9. + - - - - - - - SEPARATING THE IONS 2 MOLTEN IONIC COMPOUND + + + + +
+ ANODE
- CATHODE
When the battery is switched on,
the + IONS move to the – CATHODE
the – IONS move to the + ANODE
This gives a way to SPLIT UP IONIC COMPOUNDS: “ELECTROLYSIS”

10. + - At ANODE: Cl- e- + Cl 2Cl- → 2e- + Cl2 then: Cl + Cl Cl2 (gas)
Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt) - =
chloride ION, extra 1 electron
Cl- Cl
chlorine ATOM,
NEUTRAL
Cl2 molecule +
- chloride IONS lose their extra electrons and turn into neutral chlorine ATOMS Cl Cl
Cl-
Cl- Cl Cl
Cl-
Cl-
At ANODE: Cl e- + Cl
Both together:
2Cl- → 2e- + Cl2
then: Cl + Cl Cl2 (gas)

11. molten sodium metal sinks to bottom
Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt) =
sodium ION, missing1 electron
sodium ATOM,
NEUTRAL
Na+ + Na +
+ sodium IONS gain an extra electron and turn into neutral sodium ATOMS Na
Na+ Na
Na+ Na
Na+
Na+ Na
At CATHODE: Na+ + e Na
molten sodium metal sinks to bottom

12. MOLTEN SODIUM CHLORIDE
Example 1: Splitting up MOLTEN SODIUM CHLORIDE (salt)
- CATHODE
+ ANODE
ELECTRONS
SODIUM metal Na
CHLORINE gas Cl2
MOLTEN SODIUM CHLORIDE
Na+
Cl-
At ANODE:
Cl e- + Cl
At CATHODE:
Na+ + e Na
Cl + Cl Cl2 (gas)

13. Br- e- + Br Pb2+ + 2e- Pb At ANODE: At CATHODE: Br + Br Br2 (gas)
Example 2: Splitting up MOLTEN LEAD BROMIDE PbBr2
- CATHODE
+ ANODE
ELECTRONS
LEAD Metal Pb
BROMINE gas Br2
MOLTEN LEAD BROMIDE
Pb2+
Br-
At ANODE:
Br e- + Br
At CATHODE:
Pb2+ + 2e Pb
Br + Br Br2 (gas)
Both together:
2Br- → 2e- + Br2

14. SODIUM CHLORIDE SOLUTION NaCl (aq)
What happens when the ionic compounds are dissolved in water?
Here, water molecules break up into HYDROGEN IONS, H+ and HYDROXIDE IONS OH-
H2O  H OH-
So, in an ionic solution (eg sodium chloride solution), there will be FOUR types of ion present:
TWO from the ionic compound and TWO from the water (H+ + OH-)
SODIUM CHLORIDE SOLUTION NaCl (aq) H+
OH-
Cl-
Na+ H+
Na+
Na+ H+
OH-
Cl-
Cl-
OH-

15. IONIC SOLUTION H+
OH- H+
OH-
Cl-
Na+ H+
Na+
Na+
OH-
Cl-
Cl-
Which ions gain or lose electrons (“get discharged”) and which stay in solution?

16. + At CATHODE: 2H+ + 2e- H2 IONIC SOLUTIONS: At the CATHODE which ions?
sodium ION, missing 1 electron
hydrogen ION, missing 1 electron
Na+ H+ H
Hydrogen ATOM,
NEUTRAL
which ions? +
As HYDROGEN is LESS REACTIVE than SODIUM, it is discharged The sodium ions stay in solution.
Na+ H H+
Na+ H H+
At CATHODE: 2H+ + 2e H2

17. IONIC SOLUTIONS: At the CATHODE – halogen compounds
hydroxide ION, from water extra electron
chloride ION, extra 1 electron
Cl-
chlorine ATOM,
NEUTRAL O H Cl +
If the – ion is a HALOGEN (Cl, Br, I) it is discharged and chlorine (or Br or I) is given off and the OH - ions stay in solution H O O H Cl Cl
Cl-
Cl- H O O H Cl Cl
Cl-
Cl-
which ions?
At ANODE: Cl e- + Cl2

18. + At CATHODE: 4OH- 2H2O + O2 + 4e-
IONIC SOLUTIONS: CATHODE – non halogen compounds
hydroxide ION, OH- from water, extra electron
Oxygen atom
nitrate ION, extra 1 electron O
NO3- O H +
NO3-
NO3-
If the – ion is NOT a halogen (eg nitrate, sulphate etc) then the HYDROXIDE ions from the water are discharged to make WATER and OXYGEN gas. The other ions stay in solution. O H O H
NO3-
NO3- O H O H
which ions?
At CATHODE: 4OH H2O + O2 + 4e-

19. RULES FOR IONIC SOLUTIONS
+ ANODE
Attracts – ions (‘Anions’)
- CATHODE
Attracts + ions (‘Cations’)
If – ions are HALOGENS ie
chloride Cl-
bromide Br-
iodide I-
the HALOGEN is produced.
If + ions (metals) are MORE REACTIVE than hydrogen
K, Na, Ca, Mg, Zn, Fe
Then HYDROGEN is produced
If – ions are NOT HALOGENS
Eg sulphate SO42-,
nitrate NO3-
carbonate CO32-
OXYGEN is produced.
If + ions (metals) are LESS REACTIVE than hydrogen
Cu, Ag, Au
Then the METAL is produced

20. Zinc atoms turn into ions, and electrons travel around the circuit.
When they reach the metals cap they travel down the positive pole.
The manganese dioxide absorbs the electrons.
There is an electrolyte (ammonium chloride in this case) which is kept damp and which the ions can travel through.

21. Recipe Time
Write a recipe
of the lesson (or of your learning)