Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
sodium nitrite : NaNO2
chrome alum : KCr(SO4)2 . 12H2O
Class:
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elem=Cr
coordination
Summary:
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Chromium (III) forms a purple coordination complex with nitrite. This
complex has a fairly bright pink/purple color, which differs quite a lot
from the color of aqueous chromium (III).
Description:
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Dissolve some chrome alum, together with a large excess amount of sodium
nitrite in a small quantity of water: Both solids dissolve, the nitrite much
faster than the chrome alum. The liquid first looks green/blue, but when
more of the solids dissolve, it becomes fairly bright pink/purple.
Add a small amount of 30% HCl to the liquid: The liquid becomes golden yellow
and a brown gas mixture is produced. The golden yellow color quickly disappears
and the liquid becomes violet, like a plain solution of chromium (III) in
water.
Add some more 30% HCl: No more color changes.