Question

How many $S{\text{ }}-{\text{ }}0{\text{ }}-{\text{ }}S$ linkages are there in dithionous acid?

Answer 1

In oxyacid of sulfur, sulfur is the central atom exhibiting a tetrahedral structure when coordinated with oxygen. This contains at least one $S = O$ bond and one $S - OH$ bond. In addition to these, a chain of ${( - S - )_n}$ as in ${H_2}{S_2}{O_6}$ . Such oxyacids with $S - S$ linkages are called Thioacids.

Complete step by step answer:
The sulfur oxyacids are the acids that contain oxygen, hydrogen, and sulfur. These are divided into four groups based on their structural similarities:
1.Sulphurous acid group- these are prepared by dissolving sulphur dioxide in water. Their structure is pyramidal with three oxygen atoms on a triangle i.e. tetrahedral structure is distorted by lone pair. These are strong reducing agents and have bleaching properties.
For example, sulphurous acid ${H_2}S{O_3}$ .
2.Sulphuric acid group- these are also called oil of vitriol, produced by the lead chamber and contact processes by dissolving $S{O_3}$ in water. For example, sulphuric acid ${H_2}S{O_4}$ (oleum) and thiosulphuric acid.
3.Thionic acid group- these are a series of unstable acids with the general formula of ${H_2}{S_n}{O_6}$ where n = 2 to 6. For example, Dithionic acid ${H_2}{S_2}{O_6}$ .
4.Peroxo acid group- these are also called Marshall’s acid or Caro’s acid. The central atom sulphur has a +6-oxidation state with a peroxo group in it. These are derived from hydrogen peroxide by replacing hydrogen atoms. For example, peroxydisulfuric acid ${H_2}{S_2}{O_8}$ .
From all these series, we saw that the $S - S$ bond is present only one in the thionic acid series. For example, dithionic acid ${H_2}{S_2}{O_6}$ . The structure is shown below,

Note: All oxyacids have the acidic hydrogen bonded to an oxygen atom. i.e. $- OH$ bond. The electronegativity of the central atom and the number of O atoms are responsible for the oxyacid acidity.