Question

The number of s-s bonds in polythionic acid ${{\text{H}}_{\text{2}}}{{\text{S}}_{\text{n}}}{{\text{O}}_{\text{6}}}$ ?
A. \[{\text{n}}\]
B. \[{\text{n - 1}}\]
C. \[{\text{n - 2}}\]
D. None of these

Answer 1

Hint: Polythionic acid is an oxoacid which has a straight chain of sulfur atoms and has the chemical formula ${{\text{S}}_{\text{n}}}{{\text{(S}}{{\text{O}}_{\text{3}}}{\text{H)}}_{\text{2}}}{\text{ (n > 2)}}$. Trithionic acid \[{{\text{H}}_{\text{2}}}{{\text{S}}_{\text{3}}}{{\text{O}}_{\text{6}}}\] , tetrathionic acid \[{{\text{H}}_{\text{2}}}{{\text{S}}_{\text{4}}}{{\text{O}}_{\text{6}}}\] are simple examples. They are the conjugate acids of polythionates. Dithionic acid \[{{\text{H}}_{\text{2}}}{{\text{S}}_{\text{2}}}{{\text{O}}_{\text{6}}}\] does not belong to the polythionic acids due to strongly different properties.

Complete step by step solution:

The number of \[{\text{s - s}}\] bonds in polythionic acid \[{{\text{H}}_{\text{2}}}{{\text{S}}_{\text{n}}}{{\text{O}}_{\text{6}}}\] ​ are \[{\text{n - 1}}\]
As we can see from the diagram, number of \[{\text{s - s}}\] bonds in polythionic acid is equal to \[{\text{n - 1}}\]

Hence, option “B” is correct

Additional Information
Any of a series of unstable acids containing a short chain of sulphur atoms, and having the general formula \[{{\text{H}}_{\text{2}}}{{\text{S}}_{\text{n}}}{{\text{O}}_{\text{6}}}\] where n is \[2,{\text{ }}3,{\text{ }}4,\] or more are named as "dithionic", "trithionic", "tetrathionic", "pentathionic" acid respectively.

Note:
1. All polythionates anion contains chains of sulfur atoms attached to the terminal \[{\text{S}}{{\text{O}}_{\text{3}}}{\text{H}}\] -groups. Names of polythionic acids are determined by the number of atoms in the chain of sulfur atoms:
2. Polythionic acids with a small number of sulfur atoms in the chain \[{\text{n = 3, 4, 5, 6}}\] are the most stable. Polythionic acids are stable only in aqueous solutions, and are rapidly destroyed at higher concentrations with the release of sulfur, sulfur dioxide and - sometimes - sulfuric acid.