Question

When the gases sulphur dioxide and hydrogen sulphide mix in the presence of water, the reaction is . Here, the hydrogen sulphide is acting as

• A. an oxidising agent
• B. a reducing agent
• C. a dehydrating agent
• D. a catalyst

Answer 1

The correct option is B

a reducing agent

Explanation for correct option:

B:

• The reaction corresponding to the gain of oxygen (O) or loss of hydrogen (H) by a species is called an oxidation reaction. On the other hand, the reaction corresponding to the loss of oxygen or gain of hydrogen by a species is called a reduction reaction.
• In the given reaction, Hydrogen sulfide $\left({\mathrm{H}}_2\mathrm{S}\right)$ gains oxygen atom to form water $\left({\mathrm{H}}_2\mathrm{O}\right)$ therefore, Hydrogen sulfide is getting oxidized. Whereas, Sulphur dioxide $\left({\mathrm{SO}}_2\right)$ loses oxygen atom to form sulphur atom $\left(\mathrm{S}\right)$ thus, it is getting reduced.

${\mathrm{SO}}_2\left(\mathrm{g}\right)+2{\mathrm{H}}_2\mathrm{S}\left(\mathrm{g}\right)\to 2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{g}\right)+3\mathrm{S}\left(\mathrm{s}\right)$

• Reducing agents are the species that reduces other substance but gets oxidized in the reaction. Since Hydrogen sulfide is getting oxidized thus, it acts as a reducing agent in the reaction.

Explanation for incorrect options:

A: Oxidizing agents are the species that oxidizes other substance but gets reduced in the reaction. For example, Sulfur dioxide in the given reaction.

Since Hydrogen sulfide is getting oxidized, it cannot act as an oxidizing agent in the reaction.

C: Dehydrating agent is the one that eliminates the water molecule from the reactant molecule. For example, Calcium oxide $\left(\mathrm{CaO}\right)$.

Since the elimination of water molecule does not take place thus, hydrogen sulfide is not a dehydrating agent.

D: Catalyst is the one that speeds up any reaction without being consumed in the reaction.

Since Hydrogen sulfide is consumed in the given reaction, it cannot act as a catalyst.

Final Answer:

Hence, the correct option is B.