Question

\[{H_2}S{O_5} + {H_2}O \to {H_2}S{O_4} + {H_2}{O_2}\]
Oxidation number of sulphur in ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{5}}}$ in the above reaction is:
a) 6
b) 4
c) 5
d) 2

Answer 1

Hint: You need to know the structure of ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{5}}}$ to solve this problem. Because linkages of oxygen may be different in this structure. Calculate the total charges and equate them to zero to find out the oxidation number of sulphur.

Complete step by step answer:
We need to know the structure of the ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{5}}}$ molecule. So, let us look at the structure of ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{5}}}$ molecule.


Now let us calculate the oxidation number of sulphur in this structure. Let us take the oxidation number of sulphur as x.
The charges of oxygen in the peroxide linkages are -1 and others are -2.
So, $2\left( { + 1} \right) + 2\left( { - 1} \right) + 3\left( { - 2} \right) + x = 0$
From this, $x = + 6$
Therefore, the oxidation number of sulphur in ${{\text{H}}_{\text{2}}}{\text{S}}{{\text{O}}_{\text{5}}}$molecule is +6.

So, the correct option is (a).

Additional Information:
Oxidation number is also called oxidation state, it is the total number of electrons that an atom either gains or loses in order to form a chemical bond with another atom.
An oxidation number is a number that is assigned to an atom in a substance. The oxidation number could be positive, negative or zero, and it indicates if electrons are lost or gained. Also, we can say that oxidation number is a number that helps us keep track of electrons in an atom.

Note: You should not be confused with oxidation number and valency. Valency cannot be negative. But oxidation numbers can be negative. Also, please note that the charge on the oxygen in peroxide linkage is -1 and in normal oxygen linkage, it is -2.