Chemistry 9701 · AS & A Level · Electrochemistry

Electrochemistry — practice question

For this question, use the average oxidation state of sulfur in $\text{S}_2\text{O}_3^{2-}$ and sulfur in $\text{S}_2\text{O}_4^{2-}$. In which reaction does the underlined element show the greatest rise in oxidation state?

  • A$3\text{CrO}_4^{3-}(aq) + 8\text{H}^+(aq) \rightarrow 2\text{CrO}_4^{2-}(aq) + \text{Cr}^{3+}(aq) + 4\text{H}_2\text{O}(l)$
  • B$2\text{NO}_2(g) + \text{H}_2\text{O}(l) \rightarrow \text{HNO}_3(aq) + \text{HNO}_2(aq)$
  • C$\text{S}_2\text{O}_3^{2-}(aq) + 2\text{H}^+(aq) \rightarrow \text{S}(s) + \text{SO}_2(g) + \text{H}_2\text{O}(l)$
  • D$2\text{S}_2\text{O}_4^{2-}(aq) + \text{H}_2\text{O}(l) \rightarrow \text{S}_2\text{O}_3^{2-}(aq) + 2\text{HSO}_3^-(aq)$

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