Page 101 - Chemistry_Form_2

Chemistry
for Secondary Schools

life including photosynthesis, respiration, combustion, bleaching, digestion, and
corrosion or rusting. In a redox reaction, oxidation and reduction reactions occur
simultaneously.

A chemical reaction is said to be an oxidation reaction when its reacting substance
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combines with oxygen, or hydrogen is removed from it. It can also be a loss of
electrons from that substance, or increase in oxidation state of that substance.
On the other hand, a chemical reaction is said to be a reduction reaction when its
reacting substance combines with hydrogen, or when oxygen is removed from
that substance. It can also be a gain of electron(s) leading to the decrease in the
oxidation state of that substance.

Oxidation and reduction reactions are opposite types of reactions. During a redox
reaction, if one substance is oxidised by either gaining oxygen, losing hydrogen
or losing one or more electrons, another substance must at the same time be
reduced by losing oxygen, gaining hydrogen or gaining one or more electrons. For
example, when copper(II) oxide is heated in hydrogen gas, it is reduced to copper
metal, while the hydrogen gas is oxidised to water. In this reaction, copper(II)
oxide gets reduced because hydrogen takes away the oxygen. Hydrogen is thus a
reducing agent. Hydrogen gas gets oxidised because copper(II) oxide gives out its
oxygen to it, thus copper(II) oxide is an oxidising agent.

Another example of a redox reaction is when iron metal is heated in chlorine gas
to form iron(III) chloride.

In this reaction, iron metal is oxidised, while chlorine gas is reduced.

94 Student’s Book Form Two

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CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 94
CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 94 01/08/2025 11:20:59