Unit 1 PPA - Prep of Potassium trioxalatoferrate (III)

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Aim - prepare crystals of the above compound and calc the %yield

Method -

Hydrated ammonium iron (II) sulphate contains pale green Fe2+ ion.

This is reacted with oxalic acid.

When heated, brown precipitate appears - iron(II)oxalate.

Precipitate filtered off.

Precipitate treated with hydrogen peroxide + potassium oxalate solution (both colourless).

Hydrogen peroxide oxidises iron(II) ---> iron (III).

Potassium trioxalatoferrate(III) and dark brown iron(III)hydroxide precipitate produced.

More oxalic acid added, coverts solid precipitate to more potassium trioxalatoferrate.

Resulting green solution filtered, left in dark cupboard.

Lime green crystals appear in few days.

Evaluation - ( why yield wasn't 100% )

Complex reactions - some reached equilibrium rather then completion

Side reactions may have occurred

Impurities in initial reactants

Mass transfer loss

Losses during crystallisation - some product remains in solution.

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