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Difficulty: HardCopper: Extraction, Physical and Chemical Properties, and Compounds

When copper metal turnings are heated with concentrated tetraoxosulfate(VI) acid (H2SO4H_2SO_4), a dense gas is evolved alongside the formation of copper(II) tetraoxosulfate(VI) (CuSO4CuSO_4) and water (H2OH_2O). Which of the following correctly identifies the gaseous product evolved and the specific role of concentrated H2SO4H_2SO_4 in this chemical reaction?

  1. Sulfur(IV) oxide (SO2SO_2); concentrated H2SO4H_2SO_4 acts as an oxidizing agent.Answer
  2. B
    Hydrogen gas (H2H_2); concentrated H2SO4H_2SO_4 acts as a typical acid reacting with a metal.
  3. C
    Sulfur(VI) oxide (SO3SO_3); concentrated H2SO4H_2SO_4 acts as a dehydrating agent.
  4. D
    Hydrogen sulfide (H2SH_2S); concentrated H2SO4H_2SO_4 acts as a reducing agent.

Answer

Sulfur(IV) oxide (SO2SO_2); concentrated H2SO4H_2SO_4 acts as an oxidizing agent.
Copper is an unreactive transition metal located below hydrogen in the electrochemical series. Consequently, it does not react with dilute acids to liberate hydrogen gas. However, when heated with concentrated tetraoxosulfate(VI) acid, the acid behaves as a strong oxidizing agent rather than a typical acid. Copper is oxidized to copper(II) tetraoxosulfate(VI) (CuSO4CuSO_4), while the sulfur in H2SO4H_2SO_4 is reduced from oxidation state +6+6 to +4+4, liberating sulfur(IV) oxide gas (SO2SO_2) along with water.

Step-by-Step Solution

1
Analyze the position of copper in the electrochemical activity series.
Copper is less electropositive than hydrogen (ECu2+/Cu∘=+0.34 VE^\circ_{Cu^{2+}/Cu} = +0.34\text{ V}), meaning it cannot displace H2H_2 gas from dilute or non-oxidizing acids.
Direct single replacement of hydrogen by copper is thermodynamically unfavorable.
2
Determine the chemical action of hot concentrated tetraoxosulfate(VI) acid on copper.
Hot concentrated H2SO4H_2SO_4 is a strong oxidizing agent. It oxidizes copper from oxidation state 00 to +2+2 (Cu2+Cu^{2+}).
Oxidizing acids react with unreactive metals via redox pathways rather than acid-base displacement.
3
Formulate the balanced thermochemical equation.
Cu(s)+2H2SO4(aq)→CuSO4(aq)+2H2O(l)+SO2(g)Cu_{(s)} + 2H_2SO_{4(aq)} \rightarrow CuSO_{4(aq)} + 2H_2O_{(l)} + SO_{2(g)}
Sulfur in H2SO4H_2SO_4 (oxidation state +6+6) undergoes reduction to form sulfur(IV) oxide (SO2SO_2, oxidation state +4+4).

Key Concept

Chemical properties of copper and oxidizing behavior of concentrated tetraoxosulfate(VI) acid
Estimated Time:2m 0s
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Topics

Copper: Extraction, Physical and Chemical Properties, and Compounds

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