ILC Chemistry OL Option 2B - Electrochemistry and Extraction of Metals

Curriculum: Irish Leaving Certificate (ILC)

Level: Ordinary Level (OL)

Subject: Chemistry

Optional Topic: Option 2B

Title: Electrochemistry & Extraction of Metals

Prepared By: ExamsLogic Academic Team

1. Learning Objectives

Explain the electrochemical series at Ordinary Level.
Use metal displacement reactions to compare reactivity.
Describe electrolysis using electrodes, electrolyte, anode and cathode.
Explain electrolysis of water and copper sulfate solution.
Describe electroplating and purification of copper.
Explain why aluminium is extracted by electrolysis.
Answer OL exam-style questions on electrochemistry and metal extraction.

2. Electrochemistry Big Picture

Electrochemistry is the study of chemical reactions involving electricity.

Electrochemistry links chemical change with electrical energy.

Key Term	Meaning
Electrolyte	Liquid or solution containing ions that can conduct electricity.
Electrode	Conductor placed into the electrolyte.
Anode	Positive electrode in electrolysis.
Cathode	Negative electrode in electrolysis.
Electrolysis	Breaking down a substance using electricity.

Examiner Tip: In electrolysis, ions must be able to move. Solid ionic compounds do not conduct because ions are fixed.

3. The Electrochemical Series

The electrochemical series arranges metals in order of reactivity. More reactive metals lose electrons more easily.

More Reactive	Metal	Exam Reminder
↑	Potassium	Very reactive.
	Sodium	Reacts strongly with water.
	Calcium	Reactive metal.
	Magnesium	Burns with bright flame.
	Aluminium	Reactive but protected by oxide layer.
	Zinc	Can displace copper.
	Iron	Can displace copper.
	Copper	Less reactive than iron and zinc.
↓	Silver	Less reactive.

A more reactive metal can displace a less reactive metal from its compound.

Examiner Trap: The metal higher in the series is more reactive and can push out metals below it.

4. Displacement Reactions

A displacement reaction happens when a more reactive metal replaces a less reactive metal from a compound.

zinc + copper sulfate → zinc sulfate + copper

Reaction	Will it happen?	Reason
Zinc + copper sulfate	Yes	Zinc is more reactive than copper.
Copper + zinc sulfate	No	Copper is less reactive than zinc.
Iron + copper sulfate	Yes	Iron is more reactive than copper.

Displacement proves relative reactivity.

Common Mistake: Saying any metal can displace any other metal. Only a more reactive metal displaces a less reactive one.

5. Electrolysis

Electrolysis uses electricity to break down an ionic substance. It needs an electrolyte and two electrodes connected to a power supply.

Electrode	Charge in Electrolysis	What is attracted?
Cathode	Negative	Positive ions/cations.
Anode	Positive	Negative ions/anions.

Cations go to cathode. Anions go to anode.

Positive ions move to the negative cathode; negative ions move to the positive anode.

6. Electrolysis of Water

Water can be electrolysed when made conductive using a small amount of acid or electrolyte. It decomposes into hydrogen and oxygen.

2H₂O → 2H₂ + O₂

Electrode	Gas Formed	Test
Cathode (-)	Hydrogen	Burning splint gives a squeaky pop.
Anode (+)	Oxygen	Relights a glowing splint.

Examiner Tip: Hydrogen and oxygen are produced in a 2:1 volume ratio.

7. Electrolysis of Copper Sulfate Solution

Copper sulfate solution contains Cu²⁺ and SO₄²⁻ ions. With inert electrodes, copper is deposited at the cathode.

Cu²⁺ + 2e⁻ → Cu

Observation	Explanation
Brown/pink copper forms on cathode.	Copper ions gain electrons and become copper metal.
Blue colour may fade.	Cu²⁺ ions are removed from solution.
Gas may form at anode.	Oxygen can be produced with inert electrodes.

Examiner Trap: Copper forms at the cathode because positive Cu²⁺ ions are attracted to the negative electrode.

8. Electroplating

Electroplating coats an object with a thin layer of metal using electrolysis.

Part	Role
Object to be plated	Cathode / negative electrode.
Plating metal	Often used as anode.
Electrolyte	Solution containing ions of the plating metal.

Electroplating is used to improve appearance, prevent corrosion or give a surface special properties.

Example: A steel spoon can be silver-plated to improve appearance and corrosion resistance.

Common Mistake: The object to be plated must be the cathode, not the anode.

9. Purification of Copper

Impure copper can be purified by electrolysis.

Part	Material	What happens?
Anode	Impure copper	Copper atoms lose electrons and dissolve as Cu²⁺.
Cathode	Pure copper	Cu²⁺ ions gain electrons and form pure copper.
Electrolyte	Copper sulfate solution	Carries copper ions.
Anode sludge	Impurities	Falls below the anode.

Anode: Cu → Cu²⁺ + 2e⁻ | Cathode: Cu²⁺ + 2e⁻ → Cu

10. Extraction of Aluminium

Aluminium is very reactive, so it cannot be extracted by simple heating with carbon. It is extracted by electrolysis of molten aluminium oxide dissolved in cryolite.

Substance	Role
Aluminium oxide, Al₂O₃	Source of aluminium ions.
Cryolite	Lowers melting point and reduces energy cost.
Carbon anode	Positive electrode; reacts with oxygen to form carbon dioxide.
Carbon cathode lining	Negative electrode where aluminium forms.

Al³⁺ + 3e⁻ → Al

Molten aluminium collects at the bottom of the cell and is tapped off.

Examiner Tip: Aluminium extraction uses a lot of electricity, making recycling aluminium important.

11. Interactive Resources

Resource 1: PhET – Battery Voltage

Use for: Exploring electrochemical ideas and electrode potentials.

Open Simulator

Resource 2: ChemCollective Virtual Lab

Use for: Metal reactivity, solutions and electrochemistry-style investigations.

Open Virtual Lab

Resource 3: PhET – Sugar and Salt Solutions

Use for: Visualising ions and conductivity in solution.

Open Simulator

12. Worked Examples

Example 1: Zinc displaces copper from copper sulfate because zinc is more reactive than copper.

Example 2: In electrolysis, Cu²⁺ ions move to the cathode and gain electrons to form copper metal.

Example 3: Aluminium is extracted by electrolysis because it is too reactive to be extracted by reduction with carbon.

13. Examiner Secrets, Mistakes and Traps

Examiner Secret: In electrolysis questions, identify the ions first, then decide which electrode they move to.

Examiner Tip: Cations are positive and go to the cathode. Anions are negative and go to the anode.

Common Mistake: Saying electrons move through the solution. Ions move through the electrolyte; electrons move in the wires.

Common Mistake: Placing the object to be electroplated at the anode. It must be the cathode.

Examiner Trap: Aluminium is extracted by electrolysis, not by carbon reduction.

14. Exam Practice Questions

Q1. What is electrolysis? [2 marks]

Q2. State which ions move to the cathode and which move to the anode. [2 marks]

Q3. Explain why zinc displaces copper from copper sulfate solution. [2 marks]

Q4. Name the gases produced during electrolysis of water and give tests for each. [4 marks]

Q5. Describe electroplating and give one use. [3 marks]

Q6. Describe purification of copper by electrolysis. [5 marks]

Q7. Explain why aluminium is extracted by electrolysis. [2 marks]

MCQs with Explanations

1. The cathode in electrolysis is: A. negative B. positive C. always copper D. always gas

Answer: A. In electrolysis the cathode is negative.

2. Positive ions move to the: A. anode B. cathode C. filter paper D. burette

Answer: B. Positive ions are attracted to the negative cathode.

3. Zinc displaces copper because zinc is: A. less reactive B. more reactive C. a gas D. a plastic

Answer: B. More reactive metals displace less reactive metals.

4. Aluminium is extracted by: A. filtration B. electrolysis C. crystallisation D. chromatography

Answer: B. Aluminium is too reactive for carbon reduction.

15. Last-Minute Revision Sheet

Electrochemistry involves chemical reactions and electricity.
Electrolysis breaks down ionic substances using electricity.
Electrolytes conduct because ions move.
Cathode is negative; anode is positive in electrolysis.
Cations go to cathode; anions go to anode.
More reactive metals displace less reactive metals.
Water electrolysis makes hydrogen and oxygen in a 2:1 ratio.
Copper sulfate electrolysis deposits copper at the cathode.
Electroplating coats an object with a thin layer of metal.
Impure copper anode dissolves; pure copper forms at cathode.
Aluminium is extracted by electrolysis of molten aluminium oxide.
Cryolite lowers the melting point and saves energy.

16. Self-Assessment Checklist

I can explain the electrochemical series.
I can predict simple displacement reactions.
I can label an electrolysis cell.
I can describe electrolysis of water.
I can describe copper sulfate electrolysis.
I can explain electroplating.
I can describe copper purification.
I can explain aluminium extraction.

17. Mark Scheme

Q1. Breaking down a substance [1] using electricity [1].

Q2. Positive ions/cations move to cathode [1]; negative ions/anions move to anode [1].

Q3. Zinc is more reactive than copper [1], so it displaces copper from copper sulfate [1].

Q4. Hydrogen at cathode [1], squeaky pop test [1]; oxygen at anode [1], relights glowing splint [1].

Q5. Coating an object with a metal using electrolysis [1]; object is cathode [1]; use e.g. protection from corrosion/improved appearance [1].

Q6. Impure copper is anode [1]; pure copper is cathode [1]; copper sulfate electrolyte [1]; copper dissolves from anode as Cu²⁺ [1]; Cu²⁺ deposits as pure copper at cathode [1].

Q7. Aluminium is very reactive [1]; cannot be extracted by carbon reduction so electrolysis is used [1].

18. Missing Syllabus Additions: Cell Voltage, Simple Cells and Reactivity

The syllabus expects students to understand that different electrochemical cells can produce different voltages depending on the metals used. A simple cell uses two different metals and an electrolyte to produce a voltage.

Cell	Relative Voltage	Reason
Magnesium / copper cell	Higher	Big difference in reactivity
Zinc / copper cell	Moderate	Smaller difference in reactivity
Iron / copper cell	Lower	Even smaller difference in reactivity

Greater difference in reactivity → larger cell voltage

Simple cell idea: When two different metals are placed in an electrolyte, electrons can flow from the more reactive metal to the less reactive metal, creating a small voltage.

Examiner Tip: More reactive metals lose electrons more easily, so pairs that are far apart in the electrochemical series give bigger voltages.

19. Electrolysis of Molten Lead Bromide

A key syllabus example is the electrolysis of molten lead bromide. Because it is molten, the ions are free to move.

PbBr₂(l) → Pb(l) + Br₂(g)

Electrode	Ion Present	Half-equation	Product
Cathode (-)	Pb²⁺	Pb²⁺ + 2e^- → Pb	Lead metal
Anode (+)	Br^-	2Br^- → Br₂ + 2e^-	Bromine gas

Common Mistake: Do not call lead bromide a solution here. The syllabus example is molten lead bromide.

20. Corrosion and its Prevention

Corrosion is the gradual destruction of a metal by chemical reaction with its environment. For iron, this is called rusting.

Rusting needs iron + water + oxygen

Method of Prevention	How it works
Painting / oiling / greasing	Stops air and water reaching the metal
Plastic coating	Provides a barrier layer
Galvanising	Coating iron with zinc
Sacrificial protection	More reactive metal corrodes instead
Electroplating	Protective metal coating

Sacrificial Protection: Zinc attached to iron corrodes in preference to the iron because zinc is more reactive.

Anodising Aluminium

Anodising is a process used to make the protective oxide layer on aluminium thicker. This improves corrosion resistance and can also improve appearance.

Examiner Tip: Anodising is linked with aluminium and protection of the surface, so do not confuse it with electroplating.

21. Extraction and Uses of Sodium and Aluminium

Sodium

Sodium is very reactive and is extracted by electrolysis of molten sodium chloride.

At cathode: Na⁺ + e^- → Na

Metal	Why electrolysis is needed	Typical Uses
Sodium	Too reactive for carbon reduction	Street lamps, heat-transfer systems, making chemicals
Aluminium	Too reactive for carbon reduction	Cans, aircraft, foil, transport, construction

Recycling aluminium is important because it saves a very large amount of energy compared with extraction from ore.

Examiner Tip: A very common mark is: aluminium is recycled because extraction uses a lot of electricity.

22. d-Block Metals, Iron and Steel

The option also includes a short treatment of transition metals and the manufacture of iron and steel.

Transition Metals

They are found in the d-block of the periodic table.
They are usually good conductors.
Many form coloured compounds.
Many are used as catalysts.

Iron Extraction

Iron is extracted in the blast furnace from iron ore using carbon monoxide as the reducing agent.

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Steel

Steel is made from iron with controlled amounts of carbon and other elements. It is stronger and harder than pure iron.

Topic	Key Point
Iron	Used in construction and engineering
Steel	Iron alloy with improved properties
Environmental issue	High energy use and carbon dioxide emissions

Examiner Trap: Iron and steel are related, but steel is not pure iron. It is an alloy.

PREMIUM REVISION NOTES

1. Learning Objectives

2. Electrochemistry Big Picture

3. The Electrochemical Series

4. Displacement Reactions

5. Electrolysis

6. Electrolysis of Water

7. Electrolysis of Copper Sulfate Solution

8. Electroplating

9. Purification of Copper

10. Extraction of Aluminium

11. Interactive Resources

Resource 1: PhET – Battery Voltage

Resource 2: ChemCollective Virtual Lab

Resource 3: PhET – Sugar and Salt Solutions

12. Worked Examples

13. Examiner Secrets, Mistakes and Traps

14. Exam Practice Questions

MCQs with Explanations

15. Last-Minute Revision Sheet

16. Self-Assessment Checklist

17. Mark Scheme

18. Missing Syllabus Additions: Cell Voltage, Simple Cells and Reactivity

19. Electrolysis of Molten Lead Bromide

20. Corrosion and its Prevention

Anodising Aluminium

21. Extraction and Uses of Sodium and Aluminium

Sodium

22. d-Block Metals, Iron and Steel

Transition Metals

Iron Extraction

Steel