Chemicals:
| 0.1 M aqueous p-benzoquinone solution (1.080 g / 100 mL H2O)
| | 0.01 M aqueous of potassium iodide solution (0.166 g / 100 mL H2O)
| | conc. H2SO4
| | 0.5 % aqueous starch solution | |
Hazards and safety precautions:
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p-Benzoquinone is toxic. May be fatal if swallowed, inhaled or absorbed through skin. Severe irritant. |
 |
Conc. sulfuric acid is highly toxic. Causes severe burns. May be fatal if swallowed. May cause cancer through inhalation.
Very destructive of mucous membranes. |
Safety glasses, protective gloves and good ventilation required. The aqueous p-benzoquinone solution should be made under a
fume hood!
Experimental procedure:
Three test tubes are set up as shown in the table below.
| Test tube 1
| 1 mL of potassium iodide solution
| | Test tube 2
| 1 mL of potassium iodide solution 1 drop of conc. H2SO4
2 drops of freshly prepared p-benzoquinone solution
| | Test tube 3
| 1 mL of aqueous starch solution |
Two drops of the intensively yellow solution from T2 are added to the starch solution in T3.
Result:
Blue 'schlieren' prove the oxidation of iodide to iodine (see Photo below).
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Discussion:
· p-benzoquinone oxidizes iodide to iodine and is reduced to hydroquinone.
General experimental instructions and index of experiments
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