Question

Burning sulfur-containing coal results in the redox reactions below:

HgS + O2 ----> Hg + SO2

Hg + O2 ----> HgO

Explain why burning coal may involve redox reaction?

Answer 1

Redox reaction is a reaction in which reduction and oxidation occur simultaneously. Reduction is the gain of electrons or addition of hydrogen or removal of oxygen whereas oxidation is the loss of electrons or addition of oxygen or removal of hydrogen In the given reactions both oxidation and reduction occur simultaneously. In first reaction sulfur in mercury sulfide has - 2 oxidation number whereas sulfur in sulfur dioxide has +4 oxidation state. Thus, there is an increase in oxidation number i. e. there is Loss of electrons . Oxygen has 0 oxidation state but in product sulfur dioxide oxygen atom has - 2 oxidation number Thus, there is decrease in oxidation number i. e. there is Gain of electrons.

In second reaction oxygen is added to mercury i. e. Mercury is oxidised. Moreover oxidation state of mercury changes from

0 to +2 i. e. Increase in oxidation number. However, oxygen is reduced because oxidation number changes from 0 to - 2

Therefore, in both reaction oxidation and reduction takes place simultaneously. So, burning of sulfur containing coal is a redox reaction. Moreover, burning of coal means carbon reacts with oxygen to form carbondioxide. Here carbon is oxidised due to addition of oxygen. Moreover oxidation number increases i. e . 0 to +4. Oxygen has 0 oxidation number and in carbon dioxide oxygen atom has - 2 electron i. e. Gain of electrons. Thus, oxygen is reduced..