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Mangs 21

Magnesium reacts with oxygen to form magnesium oxide, demonstrating oxidation. Reduction is defined as the loss of oxygen, as seen when copper(II) oxide reacts with hydrogen, resulting in both oxidation and reduction occurring simultaneously in redox reactions. These reactions are significant in processes like photosynthesis and respiration, and can also lead to costly damage, such as rusting of iron.

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9 views4 pages

Mangs 21

Magnesium reacts with oxygen to form magnesium oxide, demonstrating oxidation. Reduction is defined as the loss of oxygen, as seen when copper(II) oxide reacts with hydrogen, resulting in both oxidation and reduction occurring simultaneously in redox reactions. These reactions are significant in processes like photosynthesis and respiration, and can also lead to costly damage, such as rusting of iron.

Uploaded by

Nyasha Mangoro
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© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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the magnesium combines with oxygen to form

magnesium oxide. Magnesium has been oxidised.

2Mg(s) + O2(g) 2MgO(s)

A simple definition of reduction is loss of oxygen. When

copper(II) oxide reacts with hydrogen, this is the equation

for the reaction:

CuO(s) + H2(g) Cu(s) + H2O(l)

Copper(II) oxide loses its oxygen. Copper(II) oxide has

been reduced.

But if we look carefully at the copper oxide/hydrogen

equation, we can see that oxidation is also taking place.

The hydrogen is gaining oxygen to form water. The

hydrogen has been oxidised. We can see that reduction


and oxidation have taken place together.

Oxidation and reduction always take place together.

We call the reactions in which this happens redox

reactions. Redox reactions are very important. For

example, one redox reaction – photosynthesis – provides

food for the entire planet, and another one – respiration –

keeps you alive. both are redox reactions.

We can also define reduction as addition of hydrogen to

a compound and oxidation as removal of hydrogen from

a compound. This is often seen in the reaction of organic

compounds (see page 237).

There are two other ways of finding out whether or


not a substance has been oxidised or reduced during a

chemical reaction:

■■ electron transfer

■■ changes in oxidation number.

Introduction

Some types of reactions can cost a lot of money due

to the damage they cause. Rusting is an oxidation

reaction that destroys about 20% of iron and steel

every year. Rust is hydrated iron(III) oxide. This forms

when iron reacts with oxygen in the presence of water.

Another costly example of oxidation is the reaction

between hydrogen and oxygen that is used to propel

some types of rockets into space. In this reaction, the


hydrogen is oxidised – but the oxygen is also reduced.

In fact, oxidation and reduction always take place

together, in what we call redox reactions.

Figure 7.1 A redox reaction is taking place when the fuel in

the Space Shuttle’s rockets burns.

1 a In each of the following equations, state which

reactant has been oxidised:

i PbO + H2 Pb + H2O

ii CO + Ag2O 2Ag + CO2

iii 2Mg + CO2 2MgO + C

b In each of the following equations, state which

reactant has bee

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