1. Electrolysis predictions and half equations. 19/05/2019
Starter- Write the the name and formula and charge for each ion (the first is done for you)
Anything in group 1 e.g. Sodium = Na+ 1+
Anything in group 2 e.g. Calcium =
Anything in group 3 e.g. aluminum =
Anything in group 6 e.g oxide
Anything in group 7 e.g. iodide
Hydrogen
Ammonium
Nitrate
Hydroxide
Hydrogen carbonate
Sulfate
Carbonate

2. To make prediction of what will form at the anode and cathode
Electrolysis predictions and half equations. 19/05/2019
To make prediction of what will form at the anode and cathode
To make good observations of what you see.
To explain your observations by making links to theory
To be able to write half equations for the reactions taking place at the anode and cathode.

3. Electrolysis predictions
observation
Conclusion
Substance
Anode
Cathode

4. What am I looking for ?
What you observed. Colour, smell, bubbles-this will not always be what you excepted!
Prediction-A description e.g. silver metal, orange metal fizzing, green gas, brown gas.
Metal to cathode, non-metal to anode
OR nothing ! If substance is covalent.
prediction
observation
Conclusion
Substance
Anode
Cathode
Explanation- because e.g. no free moving ions, e.g. not what I excepted at the anode another reaction must be taking place.

5. prediction
observation
Conclusion
Substance
Anode
Cathode
Ethanol
Nothing it is covalent
Light bulb did not light, it is covalent so no free moving ions or delocalized electrons.
glucose
NaCl (s)
Nothing, ions are in a fixed position cannot move
Light bulb did not light, ions are in a fixed position cannot move
NaCl (aq)
Green chlorine gas
Silver sodium metal
Anode-bubbles, smell of swimming pools. Cathode- bubbles!
Dissolved ions are free to move, something else is happening at cathode

6. prediction
observation
Conclusion
Substance
Anode
Cathode
H2SO4
SO2 ? SO3 and O2 ?
H2 gas
Light bulb light colorless gas at both electrodes.
Need further testing to find out gases identity.
CuSO4 (s)
Nothing, ions are in a fixed position cannot move
Light bulb did not light, ions are in a fixed position cannot move
CuSO4 (aq)
Orange metal formed on cathode
Anode-bubbles, cathode coating of orange metal covers Cathode
Dissolved ions are free to move, something else is happening at cathode

7. write ionic half-equations representing the re actions at the electrodes during electrolysis
Electrons carry the current through the wire.
Ions carry the current through the liquid

8. 1.54 write ionic half-equations representing the reactions at the electrodes during electrolysis
Ions become atoms or molecules
By gaining or loosing electrons
They “give” electrons to the circuit
Or “take” electrons from the circuit
To make the electricity flow.

9. 1.54 write ionic half-equations representing metal cations-easy
At the CATHODE
Pb e- --> Pb
Gains electrons
So is reduced
Cation

10. At the ANODE Br - --> Br + 1e- Br - --> Br2 + 1e-
1.54 write ionic half-equations representing non-metal anions-a wee bit harder
At the ANODE
Br - --> Br + 1e-
Br - --> Br2 + 1e-
2Br - --> Br2 + 2e-
Loses electrons
So is reduced
anion

11. Electrolysis
Cations-positive ions (metals) go to the negative electrode –Cathode
Metalx+(aq) + xe- ---> Metal (s)
Anions negative ions (non-metal) go to the positive electrode-Anode.
Non-metalx- (aq) ---> non-metal + xe-
CAUTION WITH DIATOMIC MOLECULES

12. = bromide ion
= lead ion
Anode
Cathode 12

13. O.I.L.R.I.G. Oxidation is loss of electrons
Reduction is gain of electrons 13

14. A grade work = bromide ion At the cathode:
= lead ion
At the cathode:
Pb+ gains electrons to form lead metal.
It is REDUCED.
At the anode:
Br- loses electrons to form bromine gas.
It is OXIDISED.
Anode
Cathode
A grade work 14

15. Compound
Anode
Cathode
Sodium Bromide
Potassium Iodide
Calcium Fluoride
Magnesium Oxide
Lithium Chloride

19. Sodium Bromide Potassium Iodide Calcium Fluoride Magnesium Oxide
Half equations- ions on the left. Elements on the right. Add the correct number of electrons to the appropriate side so charges on both side balance
Sodium Bromide
Potassium Iodide
Calcium Fluoride
Magnesium Oxide
Lithium Chloride
2Br > Br2 + 2e-
Na e- --> Na