Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
neodymium sulfate : Nd2(SO4)3.8H2O
sodium chromate : Na2CrO4
Class:
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elem=Cr,Nd
precipitation
Summary:
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Neodymium ions form a yellow/lime green precipitate with chromate ion.
The solubility of neodymium chromate is very low.
Neodymium dichromate is much more soluble, at least in acidic solution.
Description:
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Dissolve some sodium chromate in water: A deep yellow solution is obtained.
The solid quickly dissolves.
Dissolve some neodymium sulfate in water: A pale lavender/pink solution is
obtained. It takes a lot of time before all of the solid has dissolved.
Add the solution of neodymium sulfate to the solution of sodium chromate. The
latter is present in large excess amount: A yellow, somewhat greenish
precipitate is formed immediately. The precipitate has a flocculent appearance.
Let the precipitate settle, decant the yellow liquid and add a lot of water.
Repeat this procedure another time: A lime green/yellow precipitate remains
and the liquid above th precipitate is very pale yellow. The rinsing with
water does not lead to noticeable losses of the precipitate.
Take some of the precipitate (suspended in water) and add a small amount of
dilute hydrochloric acid: The precipitate quickly dissolves, the solution
becomes orange.