Description of experiment
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Needed compounds:
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sodium hydroxide : NaOH
potassium dichromate : K2Cr2O7
lead acetate : Pb(CH3COO)2 . 3H2O
Class:
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elem=Pb,Cr
precipitation
Summary:
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Lead (II) salts give a yellow precipitate of lead chromate with dichromates.
When this precipitate is made alkaline, then it turns orange.
Description:
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Dissolve some lead acetate in distilled water: The liquid becomes colorless
and a little opaque. It just is not completely clear.
Add a solution of potassium dichromate: Formation of a bright yellow
precipitate. The liquid above the precipitate becomes yellow as well.
Add a little amount of a solution of NaOH: Liquid remains yellow, the
precipitate becomes orange (initially a thin orange layer on the yellow
precipitate, on shaking all of it becomes orange). After a few minutes
all precipitate has settled and has formed a bright orange layer and the
liquid above it is clear and yellow.
Add much more solution of NaOH: No visible changes on both the liquid and
the precipitate.