Oxidation reaction. The name itself tells
 
us that it is related to oxygen. How?
 
Let's see, if in a reaction substance
 
gains oxygen, it will be termed as an
 
oxidation reaction. For example, if we
 
take one gram of copper powder in a dish and
 
heat it. When we heat, the copper powder
 
will be coated with black copper oxide.
 
That means copper Cu reacted with oxygen
 
that is O2 and forms copper oxide.
 
Now here this is copper oxide copper 2
 
indicates that the valency of copper is
 
2 and oxygen valency is also 2.
 
formula becomes CuO.
 
Now this is an example of oxidation
 
reaction because copper has gained
 
oxygen during the reaction. Now what if
 
oxygen is lost by a substance in a
 
reaction? What will it be called?
 
Reaction would be called as a reduction
 
reaction. For example we have mercury
 
oxide that is HgO. Hg stand for
 
mercury and O for oxygen. Valency of
 
mercury is 2 and oxygen is also 2. So
 
formula becomes HgO. Now when mercuric
 
oxide is heated oxygen is removed from
 
mercuric oxide. So the products formed are Hg
 
plus O2 because oxygen has evolved.
 
Here from mercuric oxide ,oxygen was
 
lost so this is termed as reduction
 
reaction. So when a substance loses oxygen
 
during a reaction it will be termed as reduction
 
reaction.
 
Okay, we've seen oxidation and reduction
 
in terms of oxygen. But we also can see
 
oxidation and reduction in terms of
 
hydrogen. Let us see how if a substance
 
losses hydrogen during a reaction, then
 
the reaction will be termed as oxidation
 
reaction and if a substance gains
 
hydrogen during the reaction it will be termed as
 
the reduction
 
reaction. Let's see one example, hydrogen
 
sulfide gas that is H2S reacts with
 
chlorine that is Cl2 and it forms HCl.
 
hydrochloric acid and sulphur. Now in
 
this reaction H2S is converted to S
 
that ís sulphur. Here hydrogen was
 
removed. So this is oxidation reaction
 
whereas chlorine converts to HCl
 
hydrochloric acid. Here hydrogen is
 
added, so this is reduction reaction. Now
 
if we club both the definitions of oxygen and
 
hydrogen, we get the definition of
 
oxidation as; If a substance gains oxygen
 
or losses hydrogen during a reaction the
 
reaction will be termed as oxidation
 
reaction and if a substance loses oxygen
 
and gains hydrogen during a reaction the
 
reaction will be termed as reduction
 
reaction.
 
Ok, let's concentrate on a reaction that
 
is H2S plus Cl2 gives HCl plus S.
 
In this reaction we've seen that
 
oxidation and reduction is happening
 
simultaneously. Such reactions are called
 
redox reactions. The reactions in which a
 
substance gets oxidized and another
 
substance get reduced simultaneously are
 
called  redox reactions. We can see one more
 
example of the redox and that is we
 
have copper (2) oxide that is black
 
powder. Now when hydrogen gas is  passed
 
over copper oxide, it forms water and
 
brown copper. Now in this reaction copper
 
oxide forms copper, so your oxygen is
 
removed. So this is the reduction and H
 
forms H2O, here oxygen is added. So
 
this is oxidation. So again this is an
 
example of a redox reaction.
 
Ok, now in our example copper oxide converts
 
to copper. Here reduction is happening
 
Which substance amongst copper oxide and
 
copper is getting reduced? It is a
 
substance on the reactant side, copper
 
oxide. Copper oxide is reduced to a
 
copper  and H2 forms H2O. Here  oxidation is
 
happening. So from H2 and H2O which
 
substance is getting oxidized. It is the
 
substance again on the reactant side. So
 
here H2 is oxidized to H2O. So always
 
remember one thing, the substance
 
oxidized or substance reduced is on
 
the reactant side. One more thing, the substance  that
 
gets reduced during the reaction is
 
the oxidizing agent and the substance
 
that gets oxidized doing the reaction is
 
called the reducing agent. So we can
 
define oxidizing agents as the
 
substances which provide oxygen or
 
remove hydrogen during a reaction are
 
called oxidizing agent and substances that
 
provide hydrogen and remove oxygen during
 
reactions are called reducing agents. So
 
always remember students, the oxidizing
 
agents, the reducing agents, the
 
substance that gets oxidized, the
 
substance that gets reduced all
 
four are on the reactant side. So let me give
 
you a task, If i give you a reaction MnO2
 
that is manganese dioxide plus HCl that
 
is hydrochloric acid forms MnCl2  and water
 
manganese chloride + water H2O and
 
chlorine that is Cl2. Now in this
 
reaction find out the substance reduced,
 
the substance oxidized, the oxidizing
 
agent and the reducing agent.
