OxfordAQA International GCSE Chemistry: Metals (9202) – Revision Notes

These notes condense section 3.3.1 Metals (3.3.1 a to c, 3.3.1.1 a to i and 3.3.1.2 a and b) of the OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards. The qualification is not tiered, so all of it applies to you. For full explanations and worked examples, go to the Metals study guide. When you are ready to test yourself properly, use the Metals practice questions.

Other useful pages: the course hub, the printable checklist and the free diagnostics, which show which topics need the most work.

Properties and alloys (3.3.1 a to c)

• Conduct heat and electricity: delocalised electrons move through the structure.
• Bend or hammer into shape: layers of atoms slide over each other.
• Alloy: a mixture of at least two elements, at least one a metal. Properties differ from the pure metals, often making the alloy more useful.
• Steel: iron mixed with carbon, sometimes with other metals too.
• Copper for wiring and plumbing: good conductor of heat and electricity; bends but is hard enough for pipes and tanks; does not react with water.

Method: evaluating an alloy from data

1. Read what the object has to do (carry current, resist corrosion, stay rigid, be light).
2. Pick out the property in the data that matches each need.
3. Compare with the alternatives in the table, giving a reason for rejecting each.
4. If asked for a mass, use mass of element = percentage/100 × mass of alloy.

Reactivity series (3.3.1.1 a)

Most reactive at the top:

Metal	Water	Dilute acid
Potassium	Melts, whizzes, lilac flame	Too violent to try
Sodium	Melts, fizzes, darts about	Too violent to try
Lithium	Fizzes steadily, does not melt	Very vigorous
Calcium	Sinks, fizzes, cloudy solution	Vigorous
Magnesium	Extremely slow	Rapid fizzing, warm
(carbon)
Zinc	Nothing seen	Steady bubbling
Iron	Nothing seen	Slow bubbling
Copper	None	None

General word equations:

• metal + water → metal hydroxide + hydrogen
• metal + hydrochloric acid → metal chloride + hydrogen
• metal + sulfuric acid → metal sulfate + hydrogen

Examples: 2K + 2H₂O → 2KOH + H₂; Mg + H₂SO₄ → MgSO₄ + H₂; Zn + 2HCl → ZnCl₂ + H₂.

Memory hook for the order: Keep Naughty Lions Calm, Mind Zebras Feeling Cross (K, Na, Li, Ca, Mg, Zn, Fe, Cu).

Displacement and redox (3.3.1.1 b and h)

• A more reactive metal pushes a less reactive metal out of solution.
• The atom of the added metal loses electrons: oxidised.
• The ion of the metal in solution gains electrons: reduced.
• No change seen means the added metal is less reactive.

Method: writing an ionic equation

1. Write the balanced symbol equation.
2. Rewrite each dissolved ionic compound as its separate ions.
3. Remove the spectator ions, which are the same before and after.
4. Check atoms and charges balance.

Small reminder: copper wire in silver nitrate solution. Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag. Nitrate ions are spectators, so Cu + 2Ag⁺ → Cu²⁺ + 2Ag. Copper is oxidised; silver ions are reduced. Two silver ions are needed for every copper atom because each copper atom loses two electrons.

Scrap iron and copper solution: Fe + Cu²⁺ → Fe²⁺ + Cu.

Extraction (3.3.1.1 c to e)

Where the metal sits	How it is obtained
Very unreactive (gold)	Found as the metal itself
Below carbon (zinc, iron)	Heat the oxide with carbon (reduction = removal of oxygen)
Above carbon (aluminium)	Electrolysis of a molten compound; high energy, so expensive

Blast furnace: raw materials and simple chemistry

Stage	Equation
Coke burns in hot air, heating the furnace	C + O₂ → CO₂
Carbon monoxide forms	CO₂ + C → 2CO
Ore reduced	Fe₂O₃ + 3CO → 2Fe + 3CO₂
Limestone decomposes	CaCO₃ → CaO + CO₂
Slag forms from sand impurities	CaO + SiO₂ → CaSiO₃

Raw materials: iron ore, coke, limestone, hot air. Overall with carbon: 2Fe₂O₃ + 3C → 4Fe + 3CO₂.

Method: choosing an extraction method

1. Find the metal’s position in the reactivity series (use any data the question gives).
2. Compare it with carbon.
3. Below carbon: heat the oxide with carbon; say which substance loses oxygen (reduced) and which gains it (oxidised).
4. Above carbon: electrolysis of the molten compound; mention the large energy cost.

Copper from low-grade ores (3.3.1.1 f and g)

• Phytomining: plants absorb copper compounds → plants burned → ash contains copper compounds.
• Bioleaching: bacteria produce a leachate solution containing copper compounds.
• Both avoid digging and dumping huge amounts of rock.

Electrolysis of a copper salt solution (inert carbon electrodes):

Electrode	Half equation	Seen
Cathode (−)	Cu²⁺ + 2e⁻ → Cu	Pink-brown coating
Anode (+), sulfate solution	4OH⁻ → O₂ + 2H₂O + 4e⁻	Bubbles of oxygen
Anode (+), chloride solution	2Cl⁻ → Cl₂ + 2e⁻	Pale green gas

With a copper anode instead: Cu → Cu²⁺ + 2e⁻ (the anode dissolves).

Recycling (3.3.1.1 i)

Recycle metals because extraction:

1. uses limited resources;
2. costs a lot of energy;
3. damages the environment.

Metal carbonates (3.3.1.2)

Thermal decomposition: metal carbonate → metal oxide + carbon dioxide. Applies to Mg, Cu, Zn, Ca and Li carbonates.

Carbonate	Equation	Colour change
Copper carbonate	CuCO₃ → CuO + CO₂	Green → black
Zinc carbonate	ZnCO₃ → ZnO + CO₂	White → yellow (hot) → white (cold)
Lithium carbonate	Li₂CO₃ → Li₂O + CO₂	White stays white

Sodium and potassium carbonates do not decompose at Bunsen burner temperatures.

With acids: metal carbonate + acid → salt + water + carbon dioxide. Fizzing; carbon dioxide turns limewater cloudy white.

Example: Li₂CO₃ + 2HNO₃ → 2LiNO₃ + H₂O + CO₂

Method: mass of residue after heating a carbonate

1. Write the balanced equation (most carbonates here react 1 : 1 to the oxide).
2. Work out Mᵣ of the carbonate and of the oxide.
3. Mass of oxide = mass of carbonate × Mᵣ(oxide) ÷ Mᵣ(carbonate).
4. Mass of carbon dioxide lost = starting mass − mass of oxide. Heat to constant mass in practice, so you know the reaction is complete.

Must-know distinctions

• Alloy vs compound: an alloy is a mixture; its elements are not chemically bonded in fixed proportions.
• Phytomining vs bioleaching: plants and burning vs bacteria and solution.
• Reduction by carbon vs reduction in displacement: for carbon extraction, think “oxygen removed”; for displacement and electrodes, think “electrons gained”.
• Thermal decomposition vs reaction with acid: heating gives an oxide and CO₂; acid gives a salt, water and CO₂.

Quick self-test

1. Why can a metal be hammered into a sheet?
2. Define an alloy.
3. Give the three properties that make copper good for plumbing and wiring.
4. Put these in order, most reactive first: zinc, lithium, copper, calcium.
5. Write the ionic equation for zinc reacting with iron(II) sulfate solution.
6. In question 5, which species is reduced?
7. Name the four raw materials for the blast furnace.
8. Why is aluminium not extracted by heating its oxide with carbon?
9. Write the half equation at the cathode when copper is obtained from copper chloride solution.
10. 6.20 g of copper carbonate, CuCO₃, is heated strongly until no more gas is given off. Calculate the mass of copper oxide left. (Aᵣ: Cu = 64, C = 12, O = 16)
11. Calculate the mass of carbon dioxide released when 5.00 g of zinc carbonate, ZnCO₃, decomposes fully. (Aᵣ: Zn = 65, C = 12, O = 16)
12. Name the products of magnesium carbonate reacting with dilute hydrochloric acid.

Answers

1. The layers of atoms slide over each other without the structure breaking.
2. A mixture of at least two elements, at least one of which is a metal.
3. Good conductor of heat and electricity; can be bent but hard enough for pipes or tanks; does not react with water.
4. Lithium, calcium, zinc, copper.
5. Zn + Fe²⁺ → Zn²⁺ + Fe
6. The iron(II) ions (they gain electrons).
7. Iron ore, coke, limestone and hot air.
8. Carbon is less reactive than aluminium, so it cannot take oxygen from aluminium oxide; electrolysis of the molten compound is used.
9. Cu²⁺ + 2e⁻ → Cu
10. Mᵣ CuCO₃ = 124, Mᵣ CuO = 80. Mass = 6.20 × 80/124 = 4.00 g.
11. Mᵣ ZnCO₃ = 125, Mᵣ CO₂ = 44. Mass = 5.00 × 44/125 = 1.76 g.
12. Magnesium chloride, water and carbon dioxide.

Where marks are usually lost

• Writing “free ions” instead of “delocalised electrons” when explaining conduction in a solid metal.
• Describing an alloy as “two metals bonded together”; it is a mixture and one element can be a non-metal, as carbon is in steel.
• Listing copper properties without linking each one to wiring or to pipes when the question asks why it is suitable.
• Swapping sodium and lithium in the order, or writing that calcium floats.
• Leaving the 2 off silver in Cu + 2Ag⁺ → Cu²⁺ + 2Ag, so the charges do not balance.
• Saying the metal ion is oxidised in a displacement reaction.
• Forgetting limestone in the list of blast furnace raw materials.
• Giving “aluminium is rare” as the reason it is expensive, instead of the energy used in electrolysis.
• Writing oxygen at the anode for copper chloride solution; chlorine forms there.
• Including sodium carbonate in the list of carbonates that break down in a Bunsen flame.

Official syllabus

OxfordAQA International GCSE Chemistry (9202) specification, Version 6.2, for exams May/June 2018 onwards, published by OxfordAQA. Section 3.3.1 Metals, including 3.3.1.1 The reactivity series and 3.3.1.2 Metal carbonates.