Chemistry IGCSE - Metals

Characteristics of metals

• High MP/BP

• Malleable

• Ductile

• Good conductor

Chemical reactions with metals + dilute acids

Metal + acid → salt + hydrogen gas

Chemical reactions with metals + cold water

Only very reactive metals form metal hydroxide + hydrogen

Chemical reactions with metals + steam

Less reactive metals form metal oxide + hydrogen

Uses of aluminium

• manufacture of aircrafts → low density

• manufacture of overhead cables → low density + good electrical conductivity

• food containers → resistance to corrosion

Uses of cooper

electrical wiring → good electrical conductivity

Alloy

mixture of metals with 1 or more elements

Common examples of alloys

1. Brass → mixture of copper + zinc

2. Stainless steel → mixture of iron + chromium + nickel + carbon

Alloys can be harder + stronger than pure metals → alloys more useful

Why stainless steel is used for cutlery

Hard + resistant to corroding → suitable for frequent use + washing

Why are alloys stronger in terms of structure

Alloys contain different sized atoms → distort regular layers in metal structure → layers can’t slide over each other easily → makes alloys stronger + harder

Order of reactivity

Reaction from potassium, sodium + calcium with cold water

react vigorously → produce metal hydroxide + hydrogen gas

Reaction from magnesium and steam

form magnesium oxide + hydrogen gas

Reaction from magnesium, iron, zinc, copper, silver + gold with dilute hydrochloric acid

• Magnesium, zinc, iron react → form salt + hydrogen gas

• Copper, silver, gold do not react → below hydrogen in reactivity series

Why some metals don’t react with acid or water

Metals below hydrogen in reactivity series → cannot displace hydrogen → no reaction

Displacement reaction in metals

more reactive metal displaces a less reactive metal

Order of reactivity

Magnesium > Zinc > Iron > Copper > Silver
More reactive = more likely to form positive ions

Reaction from zinc in copper(II) sulfate solution

Zinc displaces copper → forms zinc sulfate + copper metal
Zn + CuSO₄ → ZnSO₄ + Cu

Why some metals rom ions more easily than others

More reactive metals lose electrons more easily → form positive ions faster

Conditions needed for rusting of iron

1. Oxygen

2. Water

Barrier methods against rusting

1. Painting

2. Greasing

3. Coating with plastic

How barrier methods prevent rusting

Prevent oxygen + water from reaching iron surface

Galvanising

Coating iron or steel with zinc

How does galvanising prevent rusting

Zinc acts as a barrier → provides sacrificial protection

What is sacrificial protection

more reactive metal → losses electrons more easily → corrodes instead of iron → since it loses electrons more easily

How position of metal in reactivity series affect its extraction

Metals higher in reactivity series = harder to extract + usually require electrolysis

less reactive metals → extracted by chemical reduction

Iron hematite is extracted by reduction of iron in a blast furnace

Blast furnace

Burning of carbon (coke) → provide heat → produce carbon dioxide

C + O₂ → CO₂

Reduction of carbon dioxide to carbon monoxide

C + CO₂ → 2CO

Reduction of iron (III) oxide by carbon monoxide

Fe₂O₃ + 3CO → 2Fe + 3CO₂

Thermal decomposition of calcium carbonate/limestone → produce calcium oxide

CaCO₃ → CaO + CO₂

Formation of slag

CaO + SiO₂ → CaSiO₃