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Electrolysis of Aqueous Potassium Iodide

Chemistry Lab 11-B

Kersh Theva

on 20 March 2011

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Transcript of Electrolysis of Aqueous Potassium Iodide

The Electrolysis of Aqueous Potassium Iodide Question What are the products from the electrolysis of
a 1 mol/L aqueous solution of potassium iodide?
Are the observed products the ones predicted
using reduction potentials? Predictions O + 4H + 4e --> 2H O 2 (g) + - 2 (l) E = 0.815 V 0 1 I + 2e --> 2I (s) - - (aq) 2 2 E = 0.536 V 0 Oxidation 2H O + 2e --> H + 2OH (l) 2 (g) - (aq) E = -0.414 V 0 3 K + e --> K + (aq) - (s) E = -2.931 V 0 Reduction 4 3-1: -1.229 V 4-1: -3.746 V 3-2: -0.95 V 4-2: 3.467 V From this, we predict that hydrogen gas, hydroxide ions and iodine are produced. Materials U-tube
Graphite rod
Wire leads
600 mL beaker
Sheet of paper
Elastic band
Pipettes Copper wire rod
Starch solution
50 mL of 1 M KI solution
1% phenolphthalein
Power source Experiment! What do we notice? Iodine is produced Hydroxide ions are produced + - > > Anode Cathode K --> + <-- I - 2I --> I + 2e - (aq) 2 (s) - 2 - 2H O + 2e --> H + 2OH 2 (l) - 2(g) - (aq) ANODE CATHODE Overall: 2H O + 2I --> I + H + 2OH 2 (l) 2(g) - (aq) - (aq) 2(s) 0.95 volts were predicted.
Much more was required because of the concept of overvoltage. Conclusion? The products were indeed hydrogen gas, hydroxide ions, and solid iodine (as we predicted) If you repeated the electrolysis using aqueous
sodium iodide instead of aqueous potassium
iodide, would your observations change? No they would not. The reduction potential of sodium ions is similar to potassium ions (-2.711 to -2.931), and the same products can be predicted. To make potassium by electrolyzing potassium iodide, would you need to modify the procedure? The only alternative that we have discussed is using molten potassium iodide. To produce this, you must keep potassium iodide at a very high temperature.
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