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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 VO₄²⁻ 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, we can see that the half-equation for VO₄²⁻ ions indicates a reduction potential of +1.00 V. We need to find a species with a higher reduction potential to ensure a spontaneous reaction. Reviewing the table, Fe²⁺ ions provide the correct pathway for reduction since their half-equation is:
ightarrow Fe(s) ext{ with } E^0 = -0.77 V$$ However, considering the reduction from VO₄²⁻ to VO²⁺ requires identifying a reducing agent capable of donating electrons to VO₄²⁻ without reversing the process. Hence, any species with a more negative electrode potential can theoretically reduce VO₄²⁻.Step 2
Provide Explanation
Answer
When assessing the reduction potential, it is essential to determine the overall cell potential produced when combining the half-reactions. The relevant cell reaction would follow the expression:
For spontaneous reactions, the total must yield a positive voltage. The strongest reducing agent that meets these criteria usually aligns with half-cells that indicate strong oxidizing properties indicative of a reverse reaction from their standard potentials.