Page 18 - NCERT Science Class 10 English Medium

In reaction (1.31) carbon is oxidised to CO and ZnO is reduced to Zn.
In reaction (1.32) HCl is oxidised to Cl whereas MnO is reduced to MnCl .
2 2 2
From the above examples we can say that if a substance gains oxygen
or loses hydrogen during a reaction, it is oxidised. If a substance loses
oxygen or gains hydrogen during a reaction, it is reduced.
Recall Activity 1.1
Recall Activity 1.1, where a magnesium ribbon burns with a dazzling flame in air (oxygen)
Recall Activity 1.1
Recall Activity 1.1
Recall Activity 1.1
and changes into a white substance, magnesium oxide. Is magnesium being oxidised or
reduced in this reaction?
1.3 .3 .3.3 .3 HAHAVE YOU OBSERVED THE EFFECTS OF OVE YOU OBSERVED THE EFFECTS OF O OVE YOU OBSERVED THE EFFECTS OF OXIDXIDAATION
HAVE
HAVE YOU OBSERVED THE EFFECTS OFYOU OBSERVED THE EFFECTS OF OXIDXIDAATION
1 1 1 1 HA XIDATIONTION
TION
REA
REACTIONS IN EVERYDAY LIFE?
REACTIONS IN EVERYDCTIONS IN EVERYDAAY LIFE?Y LIFE?
REA
REACTIONS IN EVERYDCTIONS IN EVERYDAAY LIFE?Y LIFE?
1.3.1 Corrosion
You must have observed that iron articles are shiny when new, but get
coated with a reddish brown powder when left for some time. This process
is commonly known as rusting of iron. Some other metals also get
tarnished in this manner. Have you noticed the colour of the coating
formed on copper and silver? When a metal is attacked by substances
around it such as moisture, acids, etc., it is said to corrode and this
process is called corrosion. The black coating on silver and the green
coating on copper are other examples of corrosion.
Corrosion causes damage to car bodies, bridges, iron railings, ships
and to all objects made of metals, specially those of iron. Corrosion of
iron is a serious problem. Every year an enormous amount of money is
spent to replace damaged iron. You will learn more about corrosion in
Chapter 3.

1.3.2 Rancidity

Have you ever tasted or smelt the fat/oil containing food materials left
for a long time?
When fats and oils are oxidised, they become rancid and their smell
and taste change. Usually substances which prevent oxidation
(antioxidants) are added to foods containing fats and oil. Keeping food
in air tight containers helps to slow down oxidation. Do you know that
chips manufacturers usually flush bags of chips with gas such as
nitrogen to prevent the chips from getting oxidised ?

Q U E S T I O N S

1. Why does the colour of copper sulphate solution change when
an iron nail is dipped in it?
2. Give an example of a double displacement reaction other than
the one given in Activity 1.10.
3. Identify the substances that are oxidised and the substances ?
that are reduced in the following reactions.
(i) 4Na(s) + O (g) → 2Na O(s)
2 2
(ii) CuO(s) + H (g) → Cu(s) + H O(l)
2 2

Chemical Reactions and Equations 13

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