TmNhRhMgBrSe
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Calcium and chromate
I put calcium carbonate into k2cr2o7 to make cacro4. caco3 don't dissolve. I put na2co3 into k2cr2o7 to make k2cro4. na2co3 dissolve and solution
become yellow. Why don't the caco3 dissolve like na2co3?
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walruslover69
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If you don't have an understanding of basic solubility rules, you definitely shouldn't be working with chromates/dichromates
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TmNhRhMgBrSe
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I put some calcium nitrate into slightly acidified k2cro4 to make cacro4. some precipitate formed but solution become very orange. Why?
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TmNhRhMgBrSe
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Fuck, wrong word. I should say "why don't caco3 react with k2cr2o7 to form co2 gas?"
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vmelkon
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Quote: Originally posted by CELamCheng  | | I put some calcium nitrate into slightly acidified k2cro4 to make cacro4. some precipitate formed but solution become very orange. Why?
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It depends on the amount of acid, but when acidity is increased, the dichromate converts partially to trichromate which has a deep red color.
I think this is the reaction
Cr2O72- + CrO42- + 2 H+ ->Cr3O102- +
H2O
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TmNhRhMgBrSe
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I added a few drops of acid into the chromate so it should have a few % dichromate before adding excess calcium nitrate. All chromate should
precipitate as cacro4. The solution should contain some remaining dichromate. Is that acidic enough to form trichromate?
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vmelkon
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Probably not. According to this video, you need a very acidic solution to make trichromate
https://www.youtube.com/watch?v=Db1PsI_YXQM
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TmNhRhMgBrSe
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| Quote: Originally posted by CELamCheng | | I put some calcium nitrate into slightly acidified k2cro4 to make cacro4. some precipitate formed but solution become very orange. Why?
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I think I know why now. The calcium nitrate has some remaining nitric acid. I found out this by adding this
solution to some new calcium carbonate.
sorry for bad english
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MrHomeScientist
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Good job sticking with it and performing your own testing! It's very rewarding to figure out problems like this.
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