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