In which conversion is the metal reduced?
A Cr₂O₇²⁻ → CrO₄²⁻
B MnO₄²⁻ → MnO₄⁻
C TiO₂ → TiO₂²⁻
D VO₃⁻ → VO⁺ - AQA - A-Level Chemistry - Question 11 - 2020 - Paper 3
Question 11
In which conversion is the metal reduced?
A Cr₂O₇²⁻ → CrO₄²⁻
B MnO₄²⁻ → MnO₄⁻
C TiO₂ → TiO₂²⁻
D VO₃⁻ → VO⁺
Worked Solution & Example Answer:In which conversion is the metal reduced?
A Cr₂O₇²⁻ → CrO₄²⁻
B MnO₄²⁻ → MnO₄⁻
C TiO₂ → TiO₂²⁻
D VO₃⁻ → VO⁺ - AQA - A-Level Chemistry - Question 11 - 2020 - Paper 3
Step 1
A Cr₂O₇²⁻ → CrO₄²⁻
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Answer
In this conversion, chromium goes from a +6 oxidation state in Cr₂O₇²⁻ to a +6 oxidation state in CrO₄²⁻. Therefore, there is no reduction.
Step 2
B MnO₄²⁻ → MnO₄⁻
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Answer
Here, manganese remains in the +7 oxidation state on both sides, indicating no reduction takes place.
Step 3
C TiO₂ → TiO₂²⁻
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Answer
Titanium in TiO₂ is in the +4 oxidation state and remains so, so again no reduction occurs.
Step 4
D VO₃⁻ → VO⁺
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Answer
In this conversion, vanadium is reduced from a +5 oxidation state in VO₃⁻ to a +4 oxidation state in VO⁺. This confirms that the metal is reduced in this reaction.
