Question

Balance the following equation by oxidation number method.
$PbS + {H_2}{O_2} \to PbS{O_4} + {H_2}O$

Answer 1

Hint : Chemical equations are the reaction equation in which the reactants convert into the products. These chemical equations need to be balanced in order to follow the “Law of conservation of mass” which states that the mass can neither be created nor destroyed. In this solution, we will balance the given chemical equation using the oxidation number method.

Complete Step By Step Answer:
We know that in chemical equations the reactants get converted into the products.
In the oxidation number method, first we identify the compounds undergoing oxidation and reduction individually. Then we write separate equations for them such as one equation of oxidation reaction and second equation for reduction reaction. The oxidation states of each element is monitored in the reactant as well as product side and we see the change in the oxidation number of each element.
Now, we will see the given chemical equation:
$P{b^{ + 2}}{S^{ - 2}} + H_2^{ + 1}O_2^{ - 1} \to P{b^{ + 2}}{S^{ + 6}}O_4^{2 - } + H_2^{ + 1}{O^{ - 2}}$
In this equation, we can see that Sulphur is being oxidised and oxygen is being reduced.
Oxidation half reaction is:
$P{b^{ + 2}}{S^{ - 2}} \to P{b^{ + 2}}{S^{ + 6}}O_4^{2 - }$
Increase in oxidation number is $+ 8.$
Reduction half reaction is:
$H_2^{ + 1}O_2^{ - 1} \to H_2^{ + 1}{O^{ - 2}}$
Decrease in oxidation number for oxygen is one unit per half peroxide molecule. Hence, the decrease in oxidation number is $2.$
So, we will multiply the reduction reaction equation by $4$ and add it with the oxidation equation.
Hence, the balanced chemical equation is:
$PbS + 4{H_2}{O_2} \to PbS{O_4} + 4{H_2}O$ .

Note :
We should remember that while balancing an equation by the oxidation number method, we should take care of the number of moles or units of compounds present on the reactant and product sides. So, we need to balance these chemical equations to follow the “Law of conservation of mass” which states that the mass can neither be created nor destroyed.