Demonstration of bromine

Chemicals needed

distilled water

potassium permanganate O Xn    N   R 8-22-50/53     S (2)-60-61

potassium bromide or sodium bromide Xi

sodium hydroxide solution 7,5%  C    R 35     S (1/2)-26-37/39-45

sulphuric acid 10%  Xi   R 36/38    S (1/2)-26-30-45

under no circumstances use concentrated sulphuric acid!

Dangerous substances information

bromine  T + C   N   R 26-35-50    S (1/2)-7/9-26-45-61

bromine water T  Xi   R 23-24     S 7/9-26

Equipment needed

stand with a double sleeve and clamp
small Erlenmeyer flask (25 ml), preferably narrow-necked
test tube
plugs (preferably silicone) with hole and discharge tube
burner (preferably alcohol)

Test procedure

• Safety goggles! Exhaust hood or good ventilation. Bromine vapors are caustic and very dangerous to one's health!
• Fill the Erlenmeyer flask with 10 - 15 ml distilled water.
• Clamp the discharge tube to the test tube such that the discharge tube leads into the Erlenmeyer flask, and so, that the end of the tube ends just over the water's surface. The surface should not be touched, otherwise it can result in a recoil whereupon the experiment must be broken off.
• Take off the plug with the discharge tube, loosen the clamp and remove the test tube. Do not displace the stand or sleeve so that the apparatus can be easily put together again after the batch.
• Add 4-5 spatula-tipfuls of bromine and 1 spatula-tipful of potassium permanganate to the test tube and mix by vigorously swaying the tube back and forth.
• Add approx. 2 ml of sulphuric acid 10%, mix by carefully swaying (the salts only partially dissolve).
• Put the apparatus back together again.
• Carefully heat the reaction mixture repeatedly until it comes to a light boil. When it reaches a boil, one removes the flame for a couple of seconds. A spilling over of the reaction mixture into the receptacle is to be avoided! Brown bromine vapors develop which condense on the cold parts of the apparatus as tiny intensive red drops. The vapors dissolve in the water of the Erlenmeyer flask and color this brownish.
• If no further bromine is produced or if the vapors visibly escape from the flask, then the heating is to be terminated, the production of bromine is then soon ended.

Disposal

• If no exhaust hood is available one opens the apparatus outdoors and carries out the following steps: one pulls the plug with the discharge tube from the test tube and draws the remaining vapor out of the test tube with a hose which is connected to a water suction pump. Then vacuum up the bromine residue out of the discharge tube. If necessary one can also vacuum the Erlenmeyer flask. In no case should one vacuum the assembled aparatus with the discharge tube, otherwise implosion!
• The brominated water from the Erlenmeyer flask can be used as bromine water for other experiments. Carefully put this in a small bottle (e.g. pipette bottle) and label this properly. Bromine water is unfortunately only good from a few days to maximally a few weeks (formation of bromine and hypobromite). If one does not need it, one slowly adds diluted caustic soda solution until discoloration and then discharges it with plenty of water into the drainage.
• After cooling one alkalifies the reaction mixture with diluted caustic soda solution in order to destroy the rest of the bromine. This is then disposed of as heavy metal waste.

Elucidation

Ox.:    2 Br^- --> Br2 + 2 e^-

Red.:    MnO4^- + 8 H⁺ + 5 e^- --> Mn²⁺ + 4 H2O

Photos

Experiment before beginning heating

Experiment shortly before terminating the reaction

Literature

Experiment derived from VI.3 "Darstellung von Brom", S. 59, [3]