Question

State whether the given statement is true or false:
S-S bond is present in the acid ${{\text{H}}_{2}}{{\text{S}}_{2}}{{\text{O}}_{3}}$ (thiosulphuric acid).

Answer 1

Thiosulphuric acid is a weak dibasic acid in which the central sulphur atom exists in $+6$ oxidation state while the other sulphur atom is in $+2$ oxidation state.

Complete step by step solution: Thiosulphuric acid has the chemical formula - ${{\text{H}}_{2}}{{\text{S}}_{2}}{{\text{O}}_{3}}$. This is a dibasic acid which means that the two hydrogens can be deprotonated as ${{\text{H}}^{+}}$ ions when treated with a base.
It also means that the two hydrogen atoms are not directly attached to the central atom instead they are attached to the central atom through an oxygen atom.This is because the hydrogen attached to the central atom through oxygen is polar and thus it can be displaced by the base easily.
Now, the remaining one oxygen and sulphur atom bonds with another sulphur atom through double covalent bonds.
So, the structure of thiosulphuric acid will look like this:

Here, the central sulphur atom is in $+6$ oxidation state and another one is in $+2$ oxidation state. Thus, we see that sulphur-sulphur (S-S) bond is present in the thiosulphuric acid.
Hence, the given statement is true.

Additional information: Thiosulphuric acids are not easily isolated, but their salts are commercially available and are used in many applications like sodium thiosulphate salt is used in the iodometric determination of copper.

Note: The structure of sulphuric acid is very similar to the structure of thiosulphuric acid. The only difference is the replacement of an oxygen atom by the sulphur atom and thus its name is thiosulphuric acid. The word thio is used for sulphur group.