Metals (C9)

IGCSE Chemistry: C9.1 Properties of metals C9.2 Uses of metals C9.3 Alloys and their properties C9.4 Reactivity series C9.5 Corrosion of metals C9.6 Extraction of metals

Name and describe the physical properties of metals

Thermal and electrical conductivity: metals have delocalised electrons that can move through the metal structure and carry charge or thermal energy

Malleability and ductility: they are malleable, meaning they can be hammered into different shapes, and ductile, meaning they can be drawn into wires. This is because the layers of positive metal ions in the metal structure can move and slide over each other

Melting and boiling points: they have high melting and boiling points because there is a strong electrostatic attraction between the positive metal ions and the delocalised electrons. This strong bond requires a lot of energy to break

Describe the reaction of metals with cold water and provide an example

Metals form a metal hydroxide and hydrogen gas (more reactive metals react with cold water more vigorously and quickly)

Ex: Ca(s) + 2H₂O(l) → Ca(OH)₂(aq) + H₂(g)

Describe the reaction of metals with steam and provide an example

Metals form a metal oxide and hydrogen gas (less reactive metals react with steam more vigorously

Ex: Zn(s) + H₂O(g) → ZnO(s) + H₂(g)

Describe the physical properties of non-metals

Thermal and electrical conductivity: they do not conduct heat and electricity, as all electrons are involved in covalent bonding

Malleability and ductility: not malleable or ductile, as they are brittle when solid and easily break apart

Melting and boiling points: low melting and boiling points since many non-metals are gases at room temperature and therefore have weak electrostatic forces of attraction between molecules

Describe the uses of aluminium and explain why it is used

Manufacture of aircraft: high strength-to-weight ratio, low density, aluminium atoms have a low atomic weight

Manufacture of overhead electrical cables: good electrical conductor, delocalised electrons are free to move and carry charge, low density

Food containers: non-toxic, corrosion-resistant, form an aluminium oxide layer to reduce further oxidation

Describe the uses of copper and explain why it is used

Electrical wiring: good electrical conductor (delocalised electrons are free to move and carry charge), good ductility (able to be stretched and drawn out into a wire without breaking)

What is an alloy?

A mixture of a metal with other elements that can be harder and stronger than pure metals, and be more resistant to corrosion and extreme temperatures (these features make them more useful than pure metals)

Name and describe some types of alloys

Brass: an alloy made of copper and zinc

Stainless steel: an alloy made of iron and other elements like chromium, nickel, and carbon

Describe the structures of alloys

Irregular arrangement of atoms

Why are alloys stornger than metals?

Because they typically contain atoms of different sizes, which distorts the regular arrangement metals usually have, making it more difficult for the metal layers to slide over each other

What can alloys be used for?

Alloys can be used to make a variety of tools due to their hardness and resistance to corrosion/rusting. Stainless steel is used to make cutlery since it is resistant to rusting and its hardness

What are ferrous metals?

Alloys that contain iron (can rust)

Describe the rusting of iron, what it is, and provide an example

Chemical reaction between iron, water, and oxygen (the reddish-brown oxide product called hydrated iron (III) oxide)

Iron + water + oxygen → Hydrated iron (III) oxide

Ex: 4Fe(s) + 3O₂(g) + X H₂O(l) → 2Fe₂O₃(s) + XH₂O(l)

What are barrier methods?

Rust prevention methods by coating iron or steel with barriers preventing iron from coming into contact with oxygen or water, but if these barriers are broken or scratched it exposes the iron again

Give some expales of barrier methods

Grease, paint, oil, plastic

What is galvanizing?

Process where iron is coated in a layer of zinc

What is sacrificial protection?

When metals higher in the reactivity series are used to form a protective layer on the surface of metals lower in reactivity

Give and expample of sacrificial protection and explain it

Ex: zinc + iron

Zinc is higher in the reactivity series; therefore loses electrons more easily and reacts more easily. Zinc oxidises first and sacrifices itself to protect the iron

What is a metal ore?

A rock that contains enough of a metal to make it worthwhile extracting

What does the extraction of metals involve? Provide some examples

As many metal ores are oxides, extracting metal involves removing oxygen from the compound, making extraction a reduction process

Ex: Iron ore: haematite → blast furnace

Ex: Aluminium ore: bauxite → electrolysis

What are native metals? Provide some exaples

Native metals are very unreactive metals that are found as uncombined elements, since they don’t react easily with other substances

Ex: Gold, platinum

Metals above carbon in the reactivity series must be extracted using which method?

Electrolysis

Metals below carbon in the reactivity series must be extracted using which method?

By heating with carbon or carbon monoxide (blast furnace)

Higher metals in reactivity series =

More difficult to extract

Lower metals in reactivity series =

Easier to obtain

In a blast furnace extraction, what happens in zone 1?

In here an exothermic reaction provides heat for the furnace, so coke (carbon) burns in the hot air to form carbon dioxide

carbon + oxygen → carbon dioxide

C(s) +O₂(g) → CO₂(g)

In a blast furnace extraction, what happens in zone 2?

This zone is the main reducing agent in the furnace, so at high temperatures, coke reacts with carbon dioxide to form carbon monoxide

carbon + carbon dioxide → carbon monoxide

Co₂(g) + C(a) → 2CO(g)

In a blast furnace extraction, what happens in zone 3?

Carbon monoxide reduces the iron (III) oxide to iron (iron extracted by reduction because oxygen is removed from the iron (III) oxide). Molten iron collects at the bottom of the furnace and is tapped off.

iron(III)oxide + carbon monoxide → iron + carbon dioxide

Fe₃O₂(s) + 3CO(g) → 2Fe(l) + 3CO₂(g)

Limestone (calcium carbonate) is added to the furnace to remove impurities in the ore (calcium carbonate in limestone thermally decomposes to form calcium oxide).

calcium carbonate → calcium oxide + carbon dioxide

CaCo₃(s) → CaO(s) + Co₂(g)

Calcium oxide formed reacts with silicon dioxide—an impurity in the iron ore—to form calcium silicate (this melts and collects as a molten slag floating on top of the molten iron, which is tapped off separately)

calcium oxide + silicon dioxide → calcium silicate

CaO(s) + SiO₂(s) → CaSiO₃(l)