Convection currents in a beaker of liquid
Practical Activity for 14-16
Observing convection currents in a beaker of water.
Apparatus and Materials
For each group of students
- Bunsen burner
- Glass tube, approximately 150 mm long x 3 mm internal diameter
- Pyrex beaker, 600 ml
- Potassium manganate VII crystals
Health & Safety and Technical Notes
You need to get the potassium manganate VII crystals into the beaker of water without colouring it unduly. Put a glass tube into the beaker so that it rests on the base of the beaker. Then drop the crystal through the tube.
- Fill the beaker with water. Put individual crystals of potassium manganate VII on the bottom of the beaker, using the method suggested above.
- Heat the water gently over the Bunsen burner and observe the motion of the coloured water. For a clear effect, use a small flame and no gauze between Bunsen and beaker (Pyrex beakers do stand this).
- Note the path that the coloured water takes from the heater to the top of the water and back down again.
- When repeating the experiment you should always start with a new batch of cold water.
This experiment was safety-tested in August 2007