Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
phosphoric acid : H3PO4
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu,P
precipitation
coordination
Summary:
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Copper (II) does not form a coordination complex with phosphates and/or
phosphoric acid.
Description:
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Add some solid copper sulfate to phosphoric acid (appr. 85% by weight): The
solid only dissolves for a small part, most of it remains as small blue
crystals, floating around in the syruppy liquid.
Heat for a while: The liquid starts boiling (removing the water from the
acid) and the copper sulfate dissolves completely. After a while of boiling
there is a sky-blue liquid, consisting mainly of phosphoric acid with some
copper sulfate dissolved in it. The color of this liquid does not differ
(visibly) from the color of a solution of copper sulfate in water.
Prepare an excess amount of a solution of sodium hydroxide and add the
sky-blue liquid to this: Formation of a dirty-green-blue precipitate. The
color of this precipitate differs from the color of copper (II) hydroxide,
but no soluble phosphate - copper (II) complex is formed. The precipitate
probably is copper phosphate or basic copper phosphate.