Question

Calculate the oxidation number of the sulphur atom in
 $ {N}{{{a}}_{{2}}}{S}{{{O}}_{{3}}} $ .

Answer 1

Hint: The oxidation number of any element in a particular compound represents the number of oxidative or the reductive ability of that element. It signifies whether that particular element will either gain or lose electrons when it reacts with any other element of a different compound.

Complete Stepwise solution
We need to adopt the following steps to find out the oxidation number of sulphur atom in $ {{N}}{{{a}}_{{2}}}{{S}}{{{O}}_{{3}}} $ :
First, let us consider that the oxidation number sulphur in sodium sulphite is: ‘x’.
Now the oxidation number of sodium is always one $ \left( { + 1} \right) $ as it does not show variable oxidation state and loses one electron to attain a stable configuration. The oxidation number of oxygen is $ \left( { - 2} \right) $ . This is because it generally accepts two electrons to attain a stable octet configuration. So considering the above oxidation numbers, let us find the oxidation number of sulphur is the given compound.
 $ \left[ {\left( {{{2 \times 1}}} \right){{ + x + }}\left( {{{ - 2 \times 3}}} \right)} \right]{{ = 0}} $
In the above equation we find the oxidation state of sulphur by multiplying the number of atoms of the element with its oxidation number. This is equal to zero as the entire compound is electrically neutral. Solving the above equation we get,
 $ {{x = 6 - 2 = + 4}} $
Hence the oxidation state of sulphur is sodium sulphite is $ \left( { + 4} \right) $ . This means that the sulphur atom has lost four electrons in order to form this compound.

Note
The transition elements and the non-metals possess “variable oxidation numbers”. This is mainly due to the presence of multiple vacant orbitals. Some of the examples include iron, having oxidation states from $ \left( { + 6} \right) $ to 0. Where $ \left( { + 6} \right) $ is the highest oxidation state of iron in which it is highly oxidising in nature. The most stable state of iron is the $ \left( { + 3} \right) $ state.