Predicting feasibility and limitationsEdexcel A-Level Chemistry: Mind map

Exam questions on Predicting feasibility and limitations

1. Acidified potassium manganate(VII) solution is added to a solution of iron(II) sulfate at 298 K. Standard electrode potentials: MnO₄⁻(aq) + 8H⁺(aq) + 5e⁻ ⇌ Mn²⁺(aq) + 4H₂O(l), E° = +1.51 V; Fe³⁺(aq) + e⁻ ⇌ Fe²⁺(aq), E° = +0.77 V.
   State the relationship between E°cell and ΔS(total), and explain why a positive E°cell shows that a reaction is feasible.2 marks
2. Zinc powder is added to aqueous copper(II) sulfate at 298 K. Standard electrode potentials: Zn²⁺(aq) + 2e⁻ ⇌ Zn(s), E° = −0.76 V; Cu²⁺(aq) + 2e⁻ ⇌ Cu(s), E° = +0.34 V. Use ΔS(total) = nFE°cell / T and ln K = nFE°cell / RT, with F = 96 500 C mol⁻¹ and R = 8.31 J K⁻¹ mol⁻¹.
   Explain what the value of K shows about the extent of this reaction.2 marks
3. A technician stores acidified potassium manganate(VII) solution for use as a titrant, and finds that it stays purple for weeks. Standard electrode potentials: MnO₄⁻(aq) + 8H⁺(aq) + 5e⁻ ⇌ Mn²⁺(aq) + 4H₂O(l), E° = +1.51 V; O₂(g) + 4H⁺(aq) + 4e⁻ ⇌ 2H₂O(l), E° = +1.23 V.
   Use the data to predict whether acidified manganate(VII) ions should oxidise water to oxygen.3 marks