Commercial electrochemical cellsAQA A-Level Chemistry: Mind map

Exam questions on Commercial electrochemical cells

1. A manufacturer makes rechargeable nickel–cadmium cells for cordless power tools. The cell is based on two half-equations with standard electrode potentials: NiO(OH) + H₂O + e⁻ ⇌ Ni(OH)₂ + OH⁻, E = +0.52 V; and Cd(OH)₂ + 2e⁻ ⇌ Cd + 2OH⁻, E = −0.88 V. The electrolyte is aqueous alkali.
   Explain why this cell can be recharged.2 marks
2. A lithium cell in a mobile phone uses a lithium-containing negative electrode and a cobalt(IV) oxide positive electrode. When the cell supplies current, the simplified electrode reactions are: negative electrode, Li → Li⁺ + e⁻; positive electrode, Li⁺ + CoO₂ + e⁻ → Li⁺[CoO₂]⁻.
   Explain how the electrode reactions in this cell generate an electric current.2 marks
3. A bus company is trialling hydrogen fuel-cell buses that use an alkaline hydrogen–oxygen fuel cell. Hydrogen and oxygen are fed continuously to separate porous electrodes in contact with aqueous potassium hydroxide. The relevant electrode potentials are: O₂ + 2H₂O + 4e⁻ ⇌ 4OH⁻, E = +0.40 V; and 2H₂O + 2e⁻ ⇌ H₂ + 2OH⁻, E = −0.83 V.
   Deduce the equation for the reaction at each electrode when the cell is supplying current, and calculate the EMF of the cell.3 marks