Chemicals:
| 0.2 M aqueous solution of hydroquinone (1.101 g / 50 mL H2O)
| | 0.05 M aqueous solution of potassium bromate (418 mg / 50 mL H2O)
| | conc. sulfuric acid | |
The solution of hydroquinone should be prepared immediately before the demonstration, because it decomposes rapidly.
Hazards and safety precautions:
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Hydroquinone is probable carcinogen. Toxic. Severe skin irritant. Harmful by inhalation and ingestion. May cause
sensitization. Eye and respiratory irritant.
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Potassium bromate is a strong oxidizer - contact with combustible materials may cause fire. Harmful if swallowed. Possible
human carcinogen. Eye, skin and respiratory irritant. |
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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, suitable ventilation. Both the solution of hydroquinone and the solution of potassium
bromate should be prepared in a fume hood!
Experimental procedure:
5 drops of potassium bromate solution and 1 drop of conc. H2SO4 are added to 0.5 mL of
hydroquinone solution.
| Tet tube 1
| KBrO3 solution
| | Test tube 2
| hydroquinone solution KBrO3 solution conc.
H2SO4 |
Results:
Upon mixing hydroquinone solution with KBrO3 solution, a needle-shaped precipitate forms (Photo 1),
which is dissolved by adding 1 mL of KBrO3 solution. The solution gradually turns yellow (Photo 2).
Photo 1
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Photo 2
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Discussion:
· The oxidation of hydroquinone (colorless) to p-benzoquinone (yellow) runs over a crystalline
intermediate of the quinhydrone.
General experimental instructions and index of experiments
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