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This question is about vanadium compounds and ions - AQA - A-Level Chemistry - Question 9 - 2018 - Paper 1
Question 9
This question is about vanadium compounds and ions. Use data from Table 4 to identify the species that can be used to reduce VO₃⁻ ions to VO²⁺ in aqueous solution a... show full transcript
Worked Solution & Example Answer:This question is about vanadium compounds and ions - AQA - A-Level Chemistry - Question 9 - 2018 - Paper 1
Step 1
Identify the reducing agent
Answer
From Table 4, the species that can reduce VO₃⁻ to VO²⁺ must have a higher standard electrode potential value (E°) than that of the reduction half-equation for VO₃⁻. The relevant half-equation is:
By examining the table, we see that Fe³⁺ can be used since:
Thus, it can reduce VO₃⁻ because its E° value is lower but still positive.
Step 2
Explain the reaction
Answer
The reduction of VO₃⁻ to VO²⁺ occurs because when Fe³⁺ acts as the reducing agent, it gives electrons to the VO₃⁻ ions. The reaction proceeds as follows:
- Fe³⁺ is reduced to Fe²⁺, and in turn, it facilitates the reduction of VO₃⁻ to VO²⁺.
- Since Fe²⁺ has a higher reactivity than VO²⁺, it confirms that the reaction can occur spontaneously.