1. GALVANIC AND ELECTROLYTIC CELLS

2. REDOX REACTIONS
REDUCTION
OXIDATION
A reaction in which a substance loses electrons
A reaction in which a substance gains electrons

3. Mg → Mg2+ + 2e- oxidation reaction
reducing agent (donates electrons and so can cause reduction)
Cl e- → 2Cl- reduction reaction
oxidising agent (accepts electrons and so can cause oxidation)

4. Mg → Mg2+ + 2e- Mg is oxidised (1)
Cl e- → 2Cl- Cl2 is reduced (2)
Mg + Cl2 → MgCl2 Redox reaction
The electrons cancel each other out.
MgCl2 is an ionic compound (Mg2+ 2Cl-)
The equation shows 2 half reactions (1 and 2) that add to give the full redox reaction.

5. DIRECT ELECTRON TRANSFER
A coil of copper was placed in a silver nitrate solution
The solution became blue because copper ions were formed.
Solid silver deposited on the copper wire.

6. From the observations we can infer that:
Cu → Cu e-
Ag+ + e- → Ag
Electrons are transferred from the copper atoms on the piece of copper, to the silver ions in the silver nitrate solution.
This is a redox reaction.
This is a spontaneous reaction.

7. A GALVANIC CELL
THE ZINC-COPPER CELL

8. The following observations were made:
the zinc plate decreases in mass.
the copper plate increases in mass.
the voltmeter reading indicates that electrons flow from the zinc plate to the copper plate.
From these observations we can infer that

9. The salt bridge:
is a gel solution that connects the two electrolyte solutions that the metals dip into.
acts as a transfer medium that allows ions to flow through but prevents the two solutions mixing.
completes the circuit allowing electrons to flow through the connecting wire.

10. The redox reaction for the cell:
Zn(s) → Zn(aq) e-
Cu(aq) e- → Cu(s)
Zn(s) + Cu(aq)2+ → Zn (aq) Cu(s)
The zinc dissolves – the mass of the zinc plate decreases.
The copper plate increases in mass because copper ions deposit as copper metal.

11. The electrodes:
Each metal strip is an electrode.
Each electrode with its associated electrolyte solution, is called a half cell.
The electrode where oxidation occurs is the ANODE. It has a negative charge.
The electrode where reduction occurs is the CATHODE. It has a positive charge.

12. Zinc atoms are oxidised to Zn2+ ions (anode).
Cell notation:
Zn / Zn2+ // Cu2+ / Cu
Write the anode half reaction first – salt bridge (//) – then the cathode half reaction
Zinc atoms are oxidised to Zn2+ ions (anode).
Cu2+ ions are reduced to copper atoms (cathode). Reduction written on the Right

13. A battery is always required in this type of cell.
ELECTROLYTIC CELLS
Source of energy
Positive electrode
Negative electrode
A battery is always required in this type of cell.

14. Chemical reactions occurring in the cell:
Na+ ions are attracted to the negative electrode, where they gain electrons.
Na+(aq) + e- → Na(s)
Reduction occurs at the negative electrode – the CATHODE.

15. Cl- ions are attracted to the positive electrode, where they lose electrons.
Cl-(aq) → Cl -(g) + e-
Oxidation occurs at the positive electrode – the ANODE.

16. Comparison of galvanic and electrolytic cells.
Galvanic cell
Electrolytic cell
Produces an emf from a chemical reaction
Uses the emf of a cell to produce a chemical reaction
Chemical potential energy converted to electrical potential energy
Electrical potential energy converted to chemical potential energy
Positive terminal - cathode
Positive terminal - anode
Two containers each with an electrodes
One container with both electrodes dipping in

17. What should you be able to do?
distinguish between galvanic and electrolytic cells.
write equations for the reactions occurring in galvanic and electrolytic cells.
explain the difference between oxidation and reduction and explain why the two types of reactions go together.
label diagrams of galvanic and electrolytic cells.