Description of experiment
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Needed compounds:
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potassium dichromate : K2Cr2O7
sodium hydroxide : NaOH
sodium dithionite : Na2S2O4 . 2H2O
Class:
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elem=Cr
redox
Summary:
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Chromate is reduced by dithionite in strongly alkaline solution, but this
reaction proceeds slowly.
Description:
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Dissolve some potassium dichromate in a solution of sodium hydroxide: A yellow
liquid is formed, containing chromate [CrO4]2-.
Dissolve some sodium dithionite in a solution of sodium hydroxide: The liquid
remains colorless and clear.
Mix the two liquids and let stand for a while: At first, the mix remains
yellow, but slowly it turns green. After a few minutes the color has shifted
towards green completely and all chromate (VI) has been converted to
the green chromite (chromate (III)).