Question

The sum of oxidation state of sulphur in ${H_2}{S_2}{O_8}$is?
A.+2
B.+6
C.+7
D.+12

Answer 1

We are asked about the oxidation state of sulphur in the given compound. Oxidation state is also known as oxidation number. It is the charge on an atom of a compound when all the bonds of the atom are broken down heterolytically.

Complete answer:
The bond between O—O is known as peroxy-linkage. The compound has one peroxy-linkage. Therefore we can conclude that two of the eight oxygen atoms have -1 oxidation state and rest 6 have -2 oxidation state.
Let us consider the oxidation state of sulphur to be $x$.
Then,
$21{\text{ }} + {\text{ }}x{\text{ }} + {\text{ }}6\left( { - 2} \right){\text{ }} + {\text{ }}\left( { - 1} \right){\text{ }} = {\text{ }}0$
Or $2{\text{ }} + {\text{ }}x{\text{ }}-{\text{ }}12{\text{ }}-{\text{ }}2{\text{ }} = {\text{ }}0$
$x{\text{ }} = {\text{ }} + 12$

So, the correct answer is D.

Additional information:
Oxidation state is the total number of electrons that an atom either gains or losses in order to form a bond. Sulphur is a multivalent non-metal, abundant, tasteless and odourless. In its native form sulphur is a yellow crystalline solid. In nature it occurs as the pure element or as sulphide and sulphate minerals. Atomic mass of sulphur is $32.065u$. In the periodic table sulphur is present in group number 17. This group comprises halogens and is also known as chalcogens.

Note:
In this type of question where we need to determine the oxidation state then it becomes necessary to know the structure of the given compound. Also the unknown oxidation state should be substituted by a variable and equated by the total charge present on the compound.