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Topic: Solubility Question  (Read 3419 times)

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Offline Zamion

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Solubility Question
« on: June 18, 2007, 11:27:00 PM »
I need to know why some chemical reactions (solubility lab) consist of a change in colour but do not form a precipitate. Specifically why mixing a solution of Cr+3 and a solution of CrO4-2 causes a colour change but no precipitate forms. Also, why mixing a solution of Cr+3 and a solution of CrO4-2 causes a colour change but no precipitate forms. Thanks.

Offline DevaDevil

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Re: Solubility Question
« Reply #1 on: June 19, 2007, 02:49:23 PM »
Quote
Specifically why mixing a solution of Cr+3 and a solution of CrO4-2 causes a colour change but no precipitate forms. Also, why mixing a solution of Cr+3 and a solution of CrO4-2 causes a colour change but no precipitate forms. Thanks.

2 times the same question?

Anyway, chromate has a yellow color; dichomate (in equilibrium with chromate) an orange color, and trivalent chromium a blue-greenish color.

Mixing these will keep the ions intact, there is nothing they will precipitate with, but of course the mixture of those colors will lead to a different color. (eg. Blue and yellow mixed will lead to green of course)

Offline Zamion

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Re: Solubility Question
« Reply #2 on: June 19, 2007, 07:15:50 PM »
Sorry, meant to say Cr+2 and CrO4-2 mixed together, as well as Ni+2 and CrO4-2 mixed together. 

This makes sense, the colours were just hard to recognize/distinguish in this particular lab. I guess the solutions were just really diluted to throw us off. Thanks.

Offline organoman

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Re: Solubility Question
« Reply #3 on: June 20, 2007, 03:22:15 AM »
Precipitation occurs if compounds forming in reactions are insoluble in the solvent. while colour changes if the product formed emit in different wavelength than the reactant.

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