Chemicals:
| granulated zinc
| | 1,2-dibromopropane
| | N,N-dimethylformamide (DMF)
| | 10 - 3 M aqueous KMnO4 solution (79 mg / 500 mL)
| | 2N NaOH | |
Hazards and safety precautions:
  |
1,2-Dibromopropane is harmful if swallowed. |
 |
DMF is harmful by inhalation, ingestion or skin contact. May act as a carcinogen. Ingestion or absorption through skin may be
fatal. Exposure may result in foetal death. Long-term exposure may result in kidney or liver damage. Irritant.
|
Safety glasses, protective gloves and effective ventilation required!
Experimental procedure:
The temperature of the water in the cuvette is 40°C.
Three test tubes are set up as shown in the table below.
| Test tube 1
| zinc granule 0.5 mL 1,2-dibromopropane layered with 0.5 mL of DMF
| | Test tube 2
| 1 mL KMnO4 solution (reference solution)
| | Test tube 3
| 1 mL KMnO4 solution 1 drop NaOH |
The two liquids in test tube 1 are mixed. Within a couple of minutes a bubbling
of gas begins, becoming appreciably more violent. Via a bended glass tube extending almost to the bottom of test tube 3, the gas
is passed into a solution of potassium permanganate (mixed with a drop of NaOH).
Results:
The violet color of the KMnO4 solution turns to a blue and then a green (Photo 1). The green color
remains some time. Finally, brown flakes of manganese dioxide are formed (Photo 2).
Photo 1 |
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Photo 2 |
 Video clip (Download RealPlayer .rm file )
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