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Difficulty: MediumOxygen, Ozone, and Classification of Oxides

When dilute tetraoxosulfate(VI) acid (H2SO4\text{H}_2\text{SO}_4) is added to sodium peroxide (Na2O2\text{Na}_2\text{O}_2), hydrogen peroxide (H2O2\text{H}_2\text{O}_2) is liberated. In contrast, treating lead(IV) oxide (PbO2\text{PbO}_2) with dilute acids does not produce hydrogen peroxide. Which of the following best accounts for this chemical distinction?

  1. Sodium peroxide contains the peroxide ion (O22−\text{O}_2^{2-}), whereas lead(IV) oxide is a true dioxide containing discrete oxide ions (O2−\text{O}^{2-}).Answer
  2. B
    Lead(IV) oxide is an amphoteric oxide, whereas sodium peroxide is a neutral oxide.
  3. C
    Sodium peroxide acts purely as a dehydrating agent in acid solution, while lead(IV) oxide is a reducing agent.
  4. D
    Oxygen in sodium peroxide has an oxidation state of −2-2, whereas in lead(IV) oxide oxygen has an oxidation state of −1-1.

Answer

Sodium peroxide contains the peroxide ion (O22−\text{O}_2^{2-}), whereas lead(IV) oxide is a true dioxide containing discrete oxide ions (O2−\text{O}^{2-}).
Peroxides such as Na2O2\text{Na}_2\text{O}_2 contain the peroxide linkage (−O−O−-\text{O}-\text{O}- or O22−\text{O}_2^{2-} ion) where oxygen has an oxidation state of −1-1. When treated with dilute acids, the peroxide ion combines with hydrogen ions to yield hydrogen peroxide (H2O2\text{H}_2\text{O}_2). Dioxides such as PbO2\text{PbO}_2 contain standard oxide ions (O2−\text{O}^{2-}) paired with a quadrivalent metal ion (Pb4+\text{Pb}^{4+}); they do not contain the peroxide link and therefore cannot produce hydrogen peroxide upon reaction with dilute acids.

Step-by-Step Solution

1
Analyze the structural composition and oxidation states of oxygen in sodium peroxide (Na2O2\text{Na}_2\text{O}_2).
In Na2O2\text{Na}_2\text{O}_2, sodium is +1+1, so oxygen exists as the peroxide ion O22−\text{O}_2^{2-} with an oxidation number of −1-1.
Peroxides are characterized by the oxygen-oxygen single bond (−O−O−-\text{O}-\text{O}-) present in the O22−\text{O}_2^{2-} group.
2
Analyze the structural composition and oxidation states of oxygen in lead(IV) oxide (PbO2\text{PbO}_2).
In PbO2\text{PbO}_2, lead is in the +4+4 oxidation state, bonded to two separate oxide ions (O2−\text{O}^{2-}), where oxygen has an oxidation number of −2-2.
Dioxides contain metal atoms in high oxidation states paired with simple oxide ions (O2−\text{O}^{2-}), rather than peroxide ions.
3
Evaluate the chemical behavior of both compounds with dilute acids.
Na2O2+H2SO4→Na2SO4+H2O2\text{Na}_2\text{O}_2 + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{H}_2\text{O}_2 (liberates H2O2\text{H}_2\text{O}_2). PbO2\text{PbO}_2 does not yield H2O2\text{H}_2\text{O}_2 because it lacks the O22−\text{O}_2^{2-} link.
Only compounds containing the structural peroxide ion can form hydrogen peroxide upon acidification.

Key Concept

Distinction between peroxides (O22−\text{O}_2^{2-}) and dioxides (O2−\text{O}^{2-})
Estimated Time:1m 15s
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Topics

Oxygen, Ozone, and Classification of Oxides

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