Question

Explain the term reduction with an example involving the reaction of hydrogen sulphide with chlorine.

Answer 1

The process of reduction has a number of definitions but with the change in definitions, only the basic underlying concepts change, not the examples.
The reaction of sulphide of hydrogen and the halogen gas yields corresponding acid of that halogen and the sulphur as a side product.

Complete step-by-step answer: The question is asking us to define the term reduction by the use of a specific example involving the hydrogen sulphide and the chlorine. Now, the term reduction can be defined in three different ways based on specific concepts which would be different from each other. Reduction could be defined in terms of gain of proton, which is observed in case of the base like ammonia. It could also be defined in terms of removal of the oxygen, from a species or ion.
In the next definition, we are going to consider the nature of the element, addition or removal of which would create a difference in the species undergoing reduction. If an electropositive element is added to a species then it has undergone the process of reduction, or if an electronegative element is removed from a species, it would mean the same, that is, reduction.
The third definition is in terms of electrons. Meaning, the species which gains electrons because of any reason, it can be said that it has undergone the process of reduction.
Now as per the example, it is said that the hydrogen sulphide will react with the chlorine, and so at first we will write their chemical formulae for more clarification. The hydrogen sulphide is represented by the formula ${{H}_{2}}S$ and the chlorine is represented by the formula $C{{l}_{2}}$. Now both of them would react with each other, but before that notice that the oxidation state of sulphur in hydrogen sulphide is $-2$ and that of chlorine is zero. Now we will write the chemical equation which represents the following reaction.
${{H}_{2}}S+C{{l}_{2}}\to 2HCl+S$
Now, in the chemical reaction notice that the oxidation state of sulphur becomes zero from $-2$ hence it is being oxidised in this reaction, and the oxidation state of chlorine, became $-1$ hence it is getting reduced in this reaction because of gain of an electron.

Note: Upon reaction of hydrogen sulphide with chlorine gas, the sulphur gets oxidised as it loses electrons and becomes neutral.
And the chlorine on the other hand gets reduced because of the gain of an electron and becomes hydrochloric acid, as a product.