Chemistry · Lesson 13

Metals & compounds; extraction (Na, Ca, Al, Fe, Cu, Zn)

JAMBWAECNECO

What the syllabus asks

JAMB: Metals and their compounds: general properties, extraction of sodium, calcium, aluminium, iron, copper and tin, reactions and uses of their compounds, alloys, rusting

WAEC: Metals and their compounds: general properties of metals, reactivity (electrochemical) series, extraction of metals (Na, Ca, Al, Fe, Cu, Zn, Sn) related to position in the series, compounds of sodium, calcium, aluminium, iron, copper and zinc, alloys, corrosion and its prevention; Nigerian mineral resources

NECO: Metals and their compounds: general properties of metals, reactivity (electrochemical) series, extraction of metals (Na, Ca, Al, Fe, Cu, Zn, Sn) related to position in the series, compounds of sodium, calcium, aluminium, iron, copper and zinc, alloys, corrosion and its prevention; Nigerian mineral resources

What you will learn

State the physical and chemical properties of metals.
Use the reactivity series to predict reactions and choose extraction methods.
Describe the extraction of sodium, calcium, aluminium, iron, copper and zinc.
Describe the properties and uses of important compounds of these metals.
Name common alloys, their constituents and uses.
Explain rusting and its prevention; calculate masses of metal obtainable from ores.

Key points

Metals: lustrous, conductors, malleable, ductile; form cations; basic or amphoteric oxides.
Reactivity series: K Na Ca Mg Al Zn Fe Sn Pb (H) Cu Ag Au; displacement predicts reactions.
K–Al: electrolysis of molten compounds; Zn–Pb: carbon/CO reduction; Cu–Au: roasting or native.
Na: Downs cell (molten NaCl + CaCl₂). Al: bauxite purified, alumina electrolysed in molten cryolite.
Iron: blast furnace—coke, CO reduces Fe₂O₃, limestone forms slag.
Copper purified by electrolysis with impure anode.
Alloys: steel, stainless steel, brass (Cu/Zn), bronze (Cu/Sn), duralumin, solder.
Rust needs water and oxygen; prevent by barriers, galvanising, sacrificial metals, alloying.

Start here: Physical and chemical properties of metals

About three-quarters of the elements are metals. Look at a welder's workshop by the roadside: iron rods bent into gates, copper wires, aluminium window frames, zinc roofing sheets. Each metal is chosen for its properties.

Typical physical properties

Shiny (lustrous) when freshly cut.
Good conductors of heat and electricity (free, delocalised electrons).
Malleable and ductile: layers of ions can slide without the metallic bond breaking.
High melting and boiling points, high density (exceptions: sodium and potassium are soft and float on water; mercury is liquid).
Sonorous: ring when struck (church and school bells).

Typical chemical properties

Form positive ions by losing electrons: Na → Na⁺ + e⁻. Metals are reducing agents.
Form basic oxides (some amphoteric: Al₂O₃, ZnO, PbO).
Reactive metals displace hydrogen from dilute acids: Zn + H₂SO₄ → ZnSO₄ + H₂.
Form ionic chlorides.

Worked example 13.1

Why is copper used for electrical wiring rather than iron?

Copper is a better electrical conductor.
It is ductile, so easily drawn into wire, and does not rust.

High conductivity, ductility, corrosion resistance

Try it yourself. Give one metal that is liquid at room temperature.

Show solution

Mercury.

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Practice questions

1. Iron is extracted from its ore in the

blast furnace
Downs cell
Haber process
Contact process

Show answer

A: blast furnace
Coke reduces iron ore in a blast furnace.

2. Rusting of iron requires

oxygen only
water only
carbon(IV) oxide
oxygen and water

Show answer

D: oxygen and water
Both air and moisture are needed.

3. Aluminium is extracted by

heating bauxite alone
roasting in air
electrolysis of molten alumina in cryolite
reduction with carbon

Show answer

C: electrolysis of molten alumina in cryolite
Al is too reactive for carbon reduction.

4. Which raw materials are fed into the blast furnace?

Sulphur and air
Iron ore, coke and limestone
Bauxite and cryolite
Brine and chlorine

Show answer

B: Iron ore, coke and limestone
Coke supplies CO; limestone removes silica.

5. The ore of aluminium is

bauxite
haematite
galena
zinc blende

Show answer

A: bauxite
Al₂O₃·2H₂O.

Key words

Ore: A rock or mineral from which a metal can be extracted economically.
Extraction: Obtaining a metal from its ore.
Reduction: Removal of oxygen or gain of electrons.
Reactivity series: Metals listed in order of decreasing reactivity.
Coke: Nearly pure carbon made from coal; fuel and reducing agent.
Slag: Calcium silicate formed from impurities in the blast furnace.
Cryolite: Na₃AlF₆, used to lower the melting point of alumina.
Bauxite: Ore of aluminium (hydrated Al₂O₃).
Haematite: Ore of iron (Fe₂O₃).
Alloy: A mixture of a metal with other elements.
Galvanising: Coating iron with zinc.
Sacrificial protection: Protecting iron by attaching a more reactive metal that corrodes instead.

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