In an acidic galvanic cell, a solid iron electrode is immersed in 1.0 M Fe2+(aq) and is connected via a salt bridge to a second half-cell that contains 0.020 M KMnO4(aq) in 1.0 M H2SO4(aq) with an inert graphite electrode. When the circuit is closed, Fe2+ is oxidized while MnO4− is reduced. The cell delivers a total charge of 96.5 C before it is disconnected.
Atomic mass: Fe = 55.85 g mol−1.
(a) Write the balanced overall net-ionic equation for the spontaneous reaction that occurs in the cell under acidic conditions.
(b) Calculate the mass of iron metal lost from the iron electrode during the passage of the 96.5 C of charge.
(c) The cathode solution volume is 100.0 mL. Calculate the decrease in the concentration of MnO4− (in mol L−1) that occurs during the discharge.
(d) Determine the number of moles of H+ consumed in the reaction and predict qualitatively how the pH of the cathode solution changes as the cell operates.