1. Blueprint Paper
When specially treated paper is exposed to light it turns blue

2. Purpose
To observe a photochemical reaction

3. Demonstration
The paper was pre-treated with a mixture of potassium hexacyanoferrate(III) and iron(III) ammonium
This mixture formed the photosensitive iron(III)hexacyanoferrate(III)
Iron(III)hexacyanoferrate(III) was the source of the photosensitive Fe3+ ion that reacted with light

4. Background
1. Photochemical Reactions
2. Photoreduction Reactions

5. 1. Photochemical Reactions
A photochemical reaction is a reaction that requires light to occur
“Photo” comes from the Greek word
“photos” which means “light” 
fotos
light

6. 2. Photoreduction Reactions
In a photoreduction reaction light causes a specie to gain electrons, thus becoming less positive
For example,
Fe3+ Fe2+
Iron(III) has been photoreduced to iron(II)
light
Reducing agent

7. Conclusions
Where light hit the paper a new compound was produced by a photoreduction reaction
The new compound was iron(III)hexacyanoferrate(II) which was blue
If the paper were left in the light it would turn completely blue

8. Comments Photography relies on photoreduction reactions
Photosynthesis by plants is a photoreduction of carbon dioxide to form sugars