GCSE Chemistry revision

Metal oxides

Reactivity of metals

AQA 4.4.1.1 Foundation & Higher

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Oxidation is the gain of oxygen by a substance, for example when magnesium reacts with oxygen to form magnesium oxide.
Reduction is the loss of oxygen from a substance, for example when magnesium oxide is broken down to release pure magnesium.
These two processes always occur together — when one substance is oxidised, another is simultaneously reduced.

1. Introduction AQA

Oxidation is the gain of oxygen by a substance, for example when magnesium reacts with oxygen to form magnesium oxide.
Reduction is the loss of oxygen from a substance, for example when magnesium oxide is broken down to release pure magnesium.
These two processes always occur together — when one substance is oxidised, another is simultaneously reduced.

Most metals are reactive and will combine with oxygen in the atmosphere over time to form metal oxides.
Iron, for example, reacts with oxygen in the air to form iron oxide, commonly known as rust.
Unreactive metals such as gold are found as pure metals in nature because they are too unreactive to combine with oxygen.

2. Why Metals Exist as Metal Oxides AQA

Most metals are reactive and will combine with oxygen in the atmosphere over time to form metal oxides.
Iron, for example, reacts with oxygen in the air to form iron oxide, commonly known as rust.
Unreactive metals such as gold are found as pure metals in nature because they are too unreactive to combine with oxygen.

To obtain a pure metal from a metal oxide, the oxygen must be removed through a process called reduction.
The cheapest and most common method is to react the metal oxide with carbon, which takes the oxygen away from the metal.
For example: copper oxide + carbon copper + carbon dioxide, where the copper is reduced and the carbon is oxidised.

3. Extracting Pure Metals by Reduction AQA

To obtain a pure metal from a metal oxide, the oxygen must be removed through a process called reduction.
The cheapest and most common method is to react the metal oxide with carbon, which takes the oxygen away from the metal.
For example: copper oxide + carbon copper + carbon dioxide, where the copper is reduced and the carbon is oxidised.

Carbon is placed within the reactivity series so it can be used as a reference point for deciding which extraction method to use.
Only metals that are less reactive than carbon — such as zinc, iron, and copper — can be extracted using reduction with carbon.
Metals more reactive than carbon, such as aluminium and sodium, cannot be extracted this way and require electrolysis instead.
Electrolysis is a much more energy-intensive and expensive process compared to reduction with carbon.

4. The Reactivity Series and Carbon AQA

Carbon is placed within the reactivity series so it can be used as a reference point for deciding which extraction method to use.
Only metals that are less reactive than carbon — such as zinc, iron, and copper — can be extracted using reduction with carbon.
Metals more reactive than carbon, such as aluminium and sodium, cannot be extracted this way and require electrolysis instead.
Electrolysis is a much more energy-intensive and expensive process compared to reduction with carbon.

Iron is commonly found in nature as iron ore, which refers to metal-rich compounds from which a metal can be extracted.
The most common iron ore is haematite, which contains iron(III) oxide, Fe₂O₃.
Since iron is less reactive than carbon, reduction with carbon can be used rather than electrolysis.
The balanced equation for this reaction is: 2Fe₂O₃ + 3C → 4Fe + 3CO₂, and heat must be supplied for the reaction to occur.

5. Extracting Iron from Iron Ore AQA

Iron is commonly found in nature as iron ore, which refers to metal-rich compounds from which a metal can be extracted.
The most common iron ore is haematite, which contains iron(III) oxide, Fe₂O₃.
Since iron is less reactive than carbon, reduction with carbon can be used rather than electrolysis.
The balanced equation for this reaction is: 2Fe₂O₃ + 3C → 4Fe + 3CO₂, and heat must be supplied for the reaction to occur.

In the extraction of iron, the iron oxide is reduced (loses oxygen) to form pure iron.
At the same time, the carbon is oxidised (gains oxygen) to form carbon dioxide.
When oxidation and reduction occur simultaneously in the same reaction, it is known as a redox reaction.

6. Oxidation and Reduction in the Same Reaction AQA

In the extraction of iron, the iron oxide is reduced (loses oxygen) to form pure iron.
At the same time, the carbon is oxidised (gains oxygen) to form carbon dioxide.
When oxidation and reduction occur simultaneously in the same reaction, it is known as a redox reaction.