Convection currents in a beaker of liquid
Observing convection currents in a beaker of water.
Apparatus and materials
For each group of students
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.
a Fill the beaker with water. Put individual crystals of potassium manganate VII on the bottom of the beaker.
b Heat the water gently over the Bunsen burner and observe the motion of the dye. For a clear effect, use a small flame and no gauze between Bunsen and beaker (Pyrex beakers do stand this).
c 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-checked in August 2007
Try an ice cube with food colouring in (green is best) and the convection current is reversed. It's a great reversal of thought. Students have to understand the process.