Question

Among the following, which of the compound of sulphur has peroxide linkage?

• A. S$_2$O$_8^{2-}$
• B. S$_2$O$_6^{2-}$
• C. S$_2$O$_7^{2-}$
• D. S$_2$O$_3^{2-}$

Answer 1

Answer: (A)

S$_2$O$_8^{2-}$

Answer 2

To identify the compound with a peroxide linkage (O-O bond), we need to analyze the structure and oxidation state of sulfur in each given anion.

1. S$_2$O$_8^{2-}$ (Peroxodisulfate ion):

   • Let the oxidation state of sulfur be 'x'.

   • Assuming all oxygen atoms have an oxidation state of -2:

     2x + 8(-2) = -2 2x - 16 = -2 2x = 14 x = +7

   • Since the maximum oxidation state of sulfur is +6, an oxidation state of +7 is impossible. This indicates the presence of a peroxide (O-O) linkage, where two oxygen atoms have an oxidation state of -1.

   • If two oxygen atoms are -1 and six are -2:

     2x + 2(-1) + 6(-2) = -2 2x - 2 - 12 = -2 2x - 14 = -2 2x = 12 x = +6

   • The structure of the peroxodisulfate ion is $^-$O$_3$S-O-O-SO$_3^-$, which clearly shows an O-O (peroxide) bond.

2. S$_2$O$_6^{2-}$ (Dithionate ion):

   • Let the oxidation state of sulfur be 'x'.
   • 2x + 6(-2) = -2
   • 2x - 12 = -2
   • 2x = 10
   • x = +5
   • The structure of the dithionate ion is $^-$O$_3$S-SO$_3^-$, containing an S-S bond, but no O-O bond.

3. S$_2$O$_7^{2-}$ (Pyrosulfate or Disulfate ion):

   • Let the oxidation state of sulfur be 'x'.
   • 2x + 7(-2) = -2
   • 2x - 14 = -2
   • 2x = 12
   • x = +6
   • The structure of the pyrosulfate ion is $^-$O$_3$S-O-SO$_3^-$, containing an S-O-S linkage, but no O-O bond.

4. S$_2$O$_3^{2-}$ (Thiosulfate ion):

   • Let the average oxidation state of sulfur be 'x'.
   • 2x + 3(-2) = -2
   • 2x - 6 = -2
   • 2x = 4
   • x = +2
   • The structure of the thiosulfate ion is $S=S(O)_2^{2-}$, which has an S-S bond and S=O bonds, but no O-O bond.

Based on the analysis, only S$_2$O$_8^{2-}$ contains a peroxide linkage.