F.5 Chemistry Question 2

Question

Choose TWO suitable chemicals below to build a chemical cells with greatest voltage.
1M acidifiedpotassium permanganese solution, 1M sodium chloride solution,
1M sodium bromide solution and 1M sodium iodide solution.
You are given common apparatus and materials like connecting wire, crocodile clips, two graphite rods, a salt bridge, beakers and a voltmeter. You should discuss the chemistry of the above chemical cell and write all observation.

Answer 1

The two chemicals used would be potassium permanganate solution (KMnO4, because it is the only oxidizing agent among the 4 chemicals) and potassium iodide solution (KI, because it is the stronger reducing agent among the 4 chemicals).

The two solutions are put separately into two beakers. Dip a graphite rod to each beaker, and the two graphite rods are connected, by using crocodile clips and conducting wire, to the two ends of a voltmeter. Use a salt bridge to connect the two beakers.

On the side of potassium permanganate solution, potassium permanganate ions gain electrons from the extenal circuit, and are reduced to manganese(II) ions.
MnO4-(aq) +8H+(aq) + 5e- → Mn2+(aq) + 4H2O(l)
The purple KMnO4 solution changes to colourless.

On the side of potassium iodide solution, iodide ions and are oxidized to iodine solution, and give electrons to the external circuit.
2I-(aq) → I2(aq) + 2e-
The brown iodine solution changes to colourless.

Overall equation :
2MnO4-(aq) +16H+(aq) + 10I-(aq) → Mn2+(aq) + 4H2O(l) + 5I2(aq)