Australia's Science Forum

Hi all,
Can anyone help with a good experiment for Rayleigh's light scattering
(red sunset) for Senior Science please?
Thanks,
Liz

Hi Lizzie
some years ago I made a 'demo model' using a glass jar that was narrow but wide[ it needs to be quite retangular in shape] and about 1litre

I dissolved a very small amount of sulfur in ethanol/or methanol?? then dilute this in water in the jar, this formed a colloidal suspension that when viewed in sunlight would be yellow/orange on one side ane red/orange on the other

This worked reasonably well and lasted quite a while
regards Juliem

I have done the following prac lots of times and it works well.

Solution A is a concentrated solution of sodium thiosulfate . solution B consists of 35 ml of concentrated sulfuric acid to 200 ml of water.
In a darkened room, arrange for a strong beam of light (we use an old slide projector), to pass through a rectangular tank however a large beaker does work. This should be at least 1 litre capacity or bigger.

The following quantities are for per litre.
Add 30 ml Solution B to the water. The light should not be ffected. Now add 10 ml solution A. Reaction between thiosulfate and acid causes precipittion of particles of sulfur so small that they are called coilloidal. The colloidal particles grow slowly and finally settle to the bottom.

A few minutes after adding solution A, the particles of sulfur are big enought to scatter some of the light. The growth of the colloidal sulfur can be slowed by using more dilute solution or bay adding some ammonia solution.

This gives a good range of colour change and works well.

Good luck, Carol