Form 1:
Air and Combustion

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Reactivity series/competition for combined Oxygen

The reactivity series is a list of elements/metals according to their affinity for oxygen.

Some metals have higher affinity for Oxygen than others.

A metal/element with higher affinity for oxygen is placed higher/on top of the one less affinity.

Metals compete for combined Oxygen.

A metal/element with higher affinity for oxygen removes Oxygen from a metal lower in the reactivity series/less affinity for Oxygen.

When a metal/element gains/acquire Oxygen, the process is called Oxidation.

When metal/element donate/lose Oxygen, the process is called Reduction.

An element/metal/compound that undergoes Oxidation is called Reducing agent.

An element/metal/compound that undergoes Reduction is called Oxidizing agent.

A reaction in which both Oxidation and Reduction take place is called a Redox reaction.

Redox reaction between Magnesium and copper (II) Oxide

Procedure

Place about 2g of copper (II) oxide in a crucible with a lid.

Place another 2g of Magnesium powder into the crucible.

Mix thoroughly.

Cover the crucible with lid.

Heat strongly for five minutes.

Allow the mixture to cool. Open the lid. Observe.

Observation

Colour change from black to brown. White solid power formed.

Explanation

Magnesium is higher in the reactivity series than Copper.

It has therefore higher affinity for Oxygen than copper.

When a mixture of copper (II) oxide and Magnesium is heated, Magnesium reduces copper (II) oxide to brown copper metal and itself oxidized to Magnesium oxide.

Magnesium is the reducing agent because it undergoes oxidation process.

Copper (II) oxide is the oxidizing agent because it undergoes redox reduction process.

The mixture should be cooled before opening the lid to prevent hot brown copper from being reoxidized back to black copper (II) oxide.

The reaction of Magnesium and Copper (II) oxide is a reaction

Chemical equation

1. Copper (II) oxide (Oxidizing agent)+ Magnesium (Reducing Agent) -> Magnesium oxide + Copper
CuO(s + Mg(s) -> MgO(s) + Cu(s)

2. Zinc (II) (Oxidizing agent) + Magnesium (Reducing Agent) -> Magnesium oxide + Zinc (yellow when hot) (white ash/solid) (grey)
ZnO(s) + Mg(s) -> MgO(s) + Zn(s)

3. Zinc (II) oxide Oxidizing agent) + Carbon (Reducing Agent) -> Carbon (IV) oxide gas + Zinc (yellow when hot) (colourless gas) (grey)
ZnO(s) + C(s) -> CO2 (g) + Zn(s)

The reactivity series is used during extraction of metals from their ore. An ore is a rock containing mineral element which can be extracted for commercial purposes.

Most metallic ores occur naturally as:

(i) oxides combined with Oxygen
(ii) sulphides combined with Sulphur
(iii) carbonates combined with carbon and Oxygen.

Metallic ores that naturally occur as metallic sulphides are first roasted in air to form the corresponding oxide. Sulphur (IV) oxide gas is produced. e.g.

Copper (I) sulphide + Oxygen -> Copper (I) Oxide + Sulphur (IV) oxide
Cu2S(s) + O2 (g) -> 2Cu(s) + SO2 (g)

Zinc (II) sulphide + Oxygen -> Zinc (II) Oxide + Sulphur (IV) oxide
ZnS(s) + O2 (g) -> Zn(s) + SO2 (g)

Lead (II) sulphide + Oxygen -> Lead (II) Oxide + Sulphur (IV) oxide
PbS(s) + O2 (g) -> Pb(s) + SO2 (g)

Iron (II) sulphide + Oxygen -> Iron (II) Oxide + Sulphur (IV) oxide
FeS(s) + O2 (g) -> Fe(s) + SO2 (g)

Metallic ores that naturally occur as metallic carbonates are first heated in air.

They decompose/split to form the corresponding oxide and produce Carbon (IV) oxide gas. .e.g.

Copper (II) carbonate -> Copper (II) oxide + Carbon (IV) oxide
CuCO3(s) -> CuO(s) + CO2 (g)

Zinc (II) carbonate -> Zinc (II) oxide + Carbon (IV) oxide
ZnCO3(s) -> ZnO(s) + CO2 (g)

Lead (II) carbonate -> Lead (II) oxide + Carbon (IV) oxide
PbCO3s) -> PbO(s) + CO2 (g)

Iron (II) carbonate -> Iron (II) oxide + Carbon (IV) oxide
FeCO3(s) -> FeO(s) + CO2 (g)

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