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Blueprint Paper. When specially treated paper is exposed to light it turns blue. Purpose. To observe a photochemical reaction. Demonstration. The paper was pre-treated with a mixture of potassium hexacyanoferrate(III) and iron(III) ammonium
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Blueprint Paper When specially treated paper is exposed to light it turns blue
Purpose • To observe a photochemical reaction
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
Background 1. Photochemical Reactions 2. Photoreduction Reactions
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
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
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
Comments • Photography relies on photoreduction reactions • Photosynthesis by plants is a photoreduction of carbon dioxide to form sugars
