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Difficulty: Very hardOxidation Numbers and IUPAC Nomenclature of Redox Species

When acidified potassium heptaoxodichromate(VI), K2Cr2O7K_2Cr_2O_7, oxidizes sulfur(IV) oxide gas, SO2SO_2, the sulfur species is converted into a polyatomic oxoanion. What is the systematic IUPAC name of the resulting oxoanion, and what is the net change in the oxidation state of the sulfur atom per atom during this redox reaction?

  1. Tetraoxosulfate(VI) ion, with an increase of +2+2Answer
  2. B
    Tetraoxosulfate(VI) ion, with an increase of +6+6
  3. C
    Trioxosulfate(IV) ion, with a decrease of −2-2
  4. D
    Heptaoxodisulfate(VI) ion, with an increase of +4+4

Answer

The resulting oxoanion is the tetraoxosulfate(VI) ion, and the net change in the oxidation state of sulfur is an increase of +2+2.
In the reaction between SO2SO_2 and K2Cr2O7K_2Cr_2O_7 in acid, sulfur is oxidized from +4+4 in SO2SO_2 to +6+6 in the sulfate ion (SO42−SO_4^{2-}). The oxidation state increases by +2+2. The oxoanion SO42−SO_4^{2-} contains four oxygen atoms bonded to sulfur in the +6+6 state, which systematically names it tetraoxosulfate(VI) ion.

Step-by-Step Solution

1
Determine the oxidation state of sulfur in the reactant sulfur(IV) oxide (SO2SO_2).
In SO2SO_2, oxygen has an oxidation state of −2-2. Let xx be the oxidation state of sulfur: x+2(−2)=0⇒x=+4x + 2(-2) = 0 \Rightarrow x = +4.
Establishing the initial oxidation state is essential to calculate the oxidation state change.
2
Identify the chemical formula of the product oxoanion formed when SO2SO_2 is oxidized by acidified K2Cr2O7K_2Cr_2O_7.
Acidified dichromate oxidizes SO2SO_2 to sulfate ions, SO42−SO_4^{2-}.
Oxidation of sulfur(IV) oxide in aqueous acid yields the sulfate oxoanion.
3
Determine the oxidation state of sulfur in the product oxoanion (SO42−SO_4^{2-}) and calculate the net change.
In SO42−SO_4^{2-}, let yy be the oxidation state of sulfur: y+4(−2)=−2⇒y=+6y + 4(-2) = -2 \Rightarrow y = +6. The change in oxidation state is +6−(+4)=+2+6 - (+4) = +2 (an increase of 2).
Determining the final state gives the quantitative change required by the problem.
4
Apply systematic IUPAC nomenclature rules to name the oxoanion SO42−SO_4^{2-}.
The ion has four oxygen atoms attached to central sulfur with oxidation state +6+6, giving the name tetraoxosulfate(VI) ion.
IUPAC oxoanion rules require specifying the number of oxygen atoms (tetraoxo-), the central element root (sulfate), and its Roman numeral oxidation state ((VI)).

Key Concept

Calculation of oxidation numbers in oxoanions and systematic IUPAC nomenclature of inorganic redox species.
Estimated Time:2m 0s
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Topics

Oxidation Numbers and IUPAC Nomenclature of Redox Species

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