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Observing Photochemical Reactions Using Treated Blueprint Paper

This experiment demonstrates a photochemical reaction using specially treated blueprint paper. The paper, pre-treated with potassium hexacyanoferrate(III) and iron(III) ammonium, forms a photosensitive compound that reacts to light. When exposed to light, the photoreduction process occurs, converting iron(III) to iron(II), resulting in a blue compound, iron(III)hexacyanoferrate(II). The experiment shows how light can induce chemical changes, highlighting fundamental concepts in chemistry, including the roles of light in reactions and the principles behind photography and photosynthesis.

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Observing Photochemical Reactions Using Treated Blueprint Paper

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Presentation Transcript

  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

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