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Electrolysis of Aqueous Potassium Iodide
103
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?
Materials
Experiment!
Predictions
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)
The Electrolysis of Aqueous Potassium Iodide
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.
To make potassium by electrolyzing potassium iodide, would you need to modify the procedure?
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.
If you repeated the electrolysis using aqueous
sodium iodide instead of aqueous potassium
iodide, would your observations change?
ANODE
Iodine is produced
-
2I --> I + 2e
2 (s)
(aq)
CATHODE
>
Hydroxide ions are produced
-
2H O + 2e --> H + 2OH
2
(l)
2(g)
(aq)
+
K -->
-
<-- I
Overall:
-
2H O + 2I --> I + H + 2OH
2
(l)
2(g)
2(s)
(aq)
-
+
Anode
Cathode
What do we notice?
+
-
0
E = 0.815 V
O + 4H + 4e --> 2H O
1
(l)
(g)
2
Oxidation
0
-
E = 0.536 V
I + 2e --> 2I
2
(s)
2
(aq)
-
0
-
E = -0.414 V
2H O + 2e --> H + 2OH
3
- Copper wire rod
- Starch solution
- 50 mL of 1 M KI solution
- 1% phenolphthalein
- Power source
2
(aq)
(g)
2
(l)
Reduction
0
+
-
- U-tube
- Graphite rod
- Wire leads
- 600 mL beaker
- Sheet of paper
- Elastic band
- Pipettes
K + e --> K
E = -2.931 V
4
(s)
(aq)
3-1: -1.229 V
4-2: 3.467 V
From this, we predict that hydrogen gas, hydroxide ions and iodine are produced.
4-1: -3.746 V
3-2: -0.95 V