Metals

Slide 1 · Learning Outcomes

What you will be able to do

Metals hold up our buildings, carry our electricity and make our jikos. Most are found in rocks as compounds, and chemistry tells us how to get them out.

Name the main ores of sodium, aluminium, iron, copper and zinc.
Relate the method of extraction of a metal to its position in the reactivity series.
Describe the extraction of sodium and aluminium by electrolysis.
Describe the extraction of iron in the blast furnace, and of copper and zinc.
Describe the reactions of metals with air, water and dilute acids.
State the composition and uses of common alloys.
Explain the environmental effects of extracting metals and how to reduce them.

Key words: an ore is a rock containing a metal compound in enough quantity to make extraction economical. Extraction = reducing the metal ions to metal atoms: Mⁿ⁺ + ne⁻ → M.

Slide 2 · Reactivity decides the method

How is each metal extracted?

The more reactive a metal, the more strongly it holds on to its non-metal partner, and the harder it is to extract.

Tap a metal. Colour bar: ■ electrolysis ■ reduction with carbon/CO ■ roasting/heating ■ found native

Tap a metal.

Concentrating the ore first: crushing, then froth flotation (sulphide ores stick to froth while the rock waste, called gangue, sinks) or magnetic separation for iron ores. Sulphide ores are then roasted in air to change them to oxides.

Slide 3 · Extraction by electrolysis

Sodium and aluminium

Slide 4 · Extraction of iron

The blast furnace

Raw materials: haematite (Fe₂O₃) or magnetite (Fe₃O₄), coke (carbon), limestone (CaCO₃) and hot air.

Tap a zone of the furnace.

Pig iron from the furnace contains about 4% carbon, so it is brittle. Blowing oxygen through it removes carbon and other impurities to make steel. Waste gases (CO, N₂, CO₂) are used to pre-heat the air.

Slide 5 · Extraction of copper and zinc

From sulphide ores

Both processes produce sulphur(IV) oxide. Releasing it causes acid rain, so it is collected and used to make sulphuric(VI) acid (Contact process), which also earns money.

Slide 6 · Chemical properties

Reactions with air, water and acids

Tap a box to see what happens.

Tap a box.

Aluminium looks less reactive than it is: a thin, tough layer of Al₂O₃ protects it. Lead hardly reacts with dilute HCl or H₂SO₄ because insoluble PbCl₂/PbSO₄ coats it.

Slide 7 · Alloys and uses

Mixing metals for better properties

An alloy is a mixture of a metal with other metals (or carbon). Different-sized atoms disrupt the regular layers, so they cannot slide easily: alloys are usually harder and stronger than the pure metal, and may resist corrosion.

Activity: match each alloy to its composition

Tap an alloy, then tap its composition.

Metal	Property	Use
Aluminium	Light, good conductor, resists corrosion	Cooking pans (sufurias), power cables, window frames
Copper	Excellent electrical conductor, ductile	Electrical wiring, water pipes
Iron/steel	Strong, cheap	Building (iron sheets, bars), vehicles, tools
Zinc	More reactive than iron	Galvanising iron sheets (mabati), dry cells

Slide 8 · Metals and the environment

The cost of mining

Kenya mines gold (e.g. Kakamega, Migori), titanium sands (Kwale), soda ash (Lake Magadi) and fluorspar (Kerio Valley). Extraction brings jobs and income, but it can damage the environment.

Activity: sort the effects

Tap a card, then tap the box it belongs to.

Air pollution

Land and water damage

Ways to reduce harm

Slide 9 · Practice

Worked example and quick checks

Worked example: mass of metal from an ore

Calculate the mass of iron that can be obtained from 1000 kg of pure haematite, Fe₂O₃. (Fe = 56, O = 16)

Step 1: Molar mass of Fe₂O₃ = (2 × 56) + (3 × 16) = 160

Step 2: 160 kg of Fe₂O₃ contain 112 kg of iron

Step 3: Mass of iron = (112 ÷ 160) × 1000

Answer: 700 kg of iron

Your turn

1. Mass of aluminium in 204 kg of Al₂O₃ (Al = 27, O = 16) = kg.

2. The main ore of aluminium is .

3. In the blast furnace, the reducing agent that reacts with the iron ore is carbon .

4. Brass is an alloy of copper and .

Slide 10 · Quiz

Check your understanding

Part A: Fill in the blanks (auto-marked, 1 mark each)

1. Sodium is extracted by electrolysis of molten sodium in the Downs cell.

2. Calcium chloride is added in the Downs cell to lower the of sodium chloride.

3. In aluminium extraction, alumina is dissolved in molten .

4. The anodes in the aluminium cell must be replaced because they react with to form carbon dioxide.

5. Limestone is added to the blast furnace to remove as slag.

6. The chemical name of slag is calcium .

7. Copper pyrites has the formula .

8. Zinc blende is roasted in air to form zinc and sulphur(IV) oxide.

9. Coating iron with zinc to prevent rusting is called .

10. Bronze is an alloy of copper and .

Part B: Short answers (smart-marked against key points)

Masomotele · Masomotele Technical Training Institute (MTTI), Eldoret · Free KCSE revision