Page 168 - Chemistry ICSE Class IX

156 ICSE Chemistry – 9
ƒ Addition of an electropositive radical:
2HgCl + SnCl o Hg Cl + SnCl 4
2
2
2
2
Mercuric chloride has gained an atom of mercury and has been
reduced to mercurous chloride.
ƒ Removal of oxygen: CuO + H o Cu + H O
2
2
Copper oxide is being reduced to copper by hydrogen.
ƒ Removal of an electronegative radical:
2FeCl + H o 2FeCl + 2HCl
2
3
2
2FeCl + SnCl o 2FeCl + SnCl 4
2
2
3
–
In these examples, ferric chloride loses an electronegative ion (Cl )
and gets reduced to ferrous chloride.
Reducing Agent
What is a reducing agent
The substance which can bring about reduction of other substances is
called reducing agent. Thus, reducing agent is the substance that provides
hydrogen or removes oxygen from any other substances. Some important
reducing agents are hydrogen, hydrogen bromide, sulphur dioxide,
hydrogen sulphide, carbon, stannous chloride. A few illustrative examples
are:
(i) ZnO + C o Zn + CO (C is reducing agent)

(ii) FeO + CO o Fe + CO (CO is reducing agent)
2
–
(iii) H SO + 2HBr o SO + Br + 2H O (HBr (more correctly Br ) is reducing agent)
4
2
2
2
2
2–
(iv) H S + Cl o 2HCl + S (H S (more correctly S ) is reducing agent)
2
2
2
(v) SO + 2H O + Br o H SO + 2HBr (SO is reducing agent)
4
2
2
2
2
2
Oxidation - Reduction is Reciprocal
Oxidation and reduction always take place side by side. In the examples
given under oxidation and reduction, we have observed that if one
substance is oxidised, the other is reduced at the same time. For example
in the reaction,
reduction
2HgCl 2 + SnCl o Hg Cl 2 + SnCl 4
2
2
oxidation
HgCl is reduced to Hg Cl , and SnCl is oxidised to SnCl .
2
4
2
2
2
In the reaction,
oxidation
H S + Cl o 2HCl + S
2
2
reduction
chlorine has been reduced to hydrochloric acid, and hydrogen
sulphide has been oxidised to sulphur.
In the reaction,
reduction
CuO + H o Cu + H O
2
2
oxidation
copper oxide is reduced to copper, whereas hydrogen is oxidised to water.