PIRA Class: 6F40.11

Purpose:

To observe the scattering or longer wavelengths of light by large particles suspended in a fluid.

Description:

Pass a beam of light through a solution of sodium thiosulfate and gradually add a diluted HCl solution.

1. Place tall beaker (containing sodium thiosulfate solution only at this point) on the overhead projector. A solid matting (with a hole cut out for the base of the beaker) can be placed underneath the beaker to block out the extra projector light.

2. With the room lights dimmed and overhead projector turned on, have students note the white color of the circle (representing the sun) on the screen.

3. Add a tiny bit of diluted HCl solution to the sodium thiosulfate solution and stir. A chemical reaction will take place in which larger particles are formed.

4. Note any changes in the color of the "sun" beam on the screen and any changes in the color of the light scattered from the sides of the solution. Within a few seconds more and more of these are formed and the white "sun" beam will gradually change from white to light yellow to yellow and then to an orangish yellow. Continue observations until you have obtained a yellow/ orange sun beam on the screen and a blue "sky" about the beaker.

Equipment:

Sunset Package: diluted HCl, Sodium Thiosulfate, tall cylinder, long spoon, black overhead projector

cover w/ hole

Support Equipment:

Overhead projector

Location:

Unknown

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