CD3 Seeing colours

In this activity you can examine the nature of the light reaching your eye from coloured solutions and from coloured surfaces

Requirements

• hand-held direct-vision spectroscope (or diffraction grating)
• test-tubes and rack
• white light source or sunlight (an ordinary light bulb can be used, but it must be in a shade or a protective holder)
• aqueous solutions of a range of coloured compounds, for example:

-         copper(II) sulphate

-         chromium(III) chloride

-         potassium dichromate(VI)

-         screened Methyl Orange indicator

• protective gloves
• brightly coloured surfaces (such as exercise books or files)

What you do

Point the spectroscope at a window or source of white light and observe the effect it has on the light.

 

Investigate the effect of placing a coloured solution between the white light source and the spectroscope.  Summarise your observations in a table.

 

Now point the spectroscope at a well-lit brightly coloured surface such as an exercise book or file.  You may want to read Chemical Ideas 6.7 to help you explain your observations.

Questions

a        What effect does the spectroscope have on white light?

 

 

b        Describe what you observed when a coloured solution was placed between the white light source and the spectroscope.  Explain why this happens.

 

 

c         Use your observations with coloured surfaces to help you write a short explanation of why paintings appear coloured when you look at them with the naked eye.