Question

Calculate oxidation number of $ S $ in $ {{H}_{2}}{{S}_{2}}{{O}_{7}} $ .

Answer 1

Hint :Oxidation number of any compound can be found out by a simple formula, total charge of the compound is zero, thus oxidation number of each element can be multiplied by its corresponding number of atoms in the compound and then find the missing oxidation number.

Complete Step By Step Answer:
The oxidation number of sulphur ( $ S $ ) in $ {{H}_{2}}{{S}_{2}}{{O}_{7}} $ is +6, that is positive six.
The given compound is known as disulphuric acid, it is formed by the reaction of fumes of sulphur trioxide ( $ S{{O}_{3}} $ ) with sulphuric acid ( $ {{H}_{2}}S{{O}_{4}} $ ).
Let us calculate the oxidation number of sulphur ( $ S $ ), to calculate the unknown oxidation number of an element in a compound, we have to first check the charge on the compound. The given compound is neutral, thus the charge on it is zero.
Now, to find the oxidation number, we have to multiply the known oxidation numbers of other elements with their respective amount of atoms and then equate them with zero, the total charge of the compound.
Now, as we have to find the oxidation number of sulphur, let us take its oxidation number as ‘x’.
There are two atoms of hydrogen, two atoms of sulphur and seven atoms of oxygen in the given compound. Now, we know that the general oxidation number of hydrogen and oxygen are +1, positive one, and -2, negative two, respectively.
The equation to find the oxidation number of sulphur is shown below,
2 (oxidation number of hydrogen) + 2 (oxidation number of sulphur) + 7 (oxidation number of oxygen) = 0
Thus, by putting the oxidation number of respective elements,
 $ 2(+1)+2(x)+7(-2)=0 $
Therefore, $ 2+2x-14=0 $
Therefore, $ 2x=12 $
Therefore, $ x=6 $
Thus, the oxidation number of sulphur ( $ S $ ) in disulphuric acid ( $ {{H}_{2}}{{S}_{2}}{{O}_{7}} $ ) is +6.

Note :
Another method can also be used to find out the oxidation number of sulphur in sulphuric acid, by looking at its structure we can say that when oxygen breaks the bond with sulphur, it will get -1 charge as it is highly electronegative than sulphur. And thus, sulphur will get +1 charge on it, as there are six bonds formed between each sulphur and oxygen, the charge on each sulphur atom will be +6.