I'm confused, in the reaction:$$\ce{K_2CrO_{4(aq)} + Ba(NO_3)_{2(aq)}\rightleftharpoons BaCrO_{4(s)} + 2KNO_{3(aq)}}$$ I got a white precipitate in an opaque yellow solution and I was told that the white precipitate was $\ce{BaCrO_4}$ but while searching on Internet I found that its color is yellow, and that the $\ce{KNO_{3(aq)}}$ is white, so my question is what is true? or what causes the color of the final solution?
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2$\begingroup$ I obtained barium chromate once, it is indeed bright yellow. I still can believe that fine dust may look pale enough to be confused with white, especially if the lights are inappropriate, but it is unlikely. $\endgroup$– permeakraCommented Sep 26, 2014 at 9:39
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$\begingroup$ maybe there was an interference in our reagents $\endgroup$– user162485Commented Sep 26, 2014 at 12:17
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$\begingroup$ Certainly $\ce{KNO3}$ is highly soluble. $\endgroup$– Geoff HutchisonCommented Sep 26, 2014 at 17:31
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1$\begingroup$ ${\ce KNO_3}$ is definitely not the precipitate, nor should it be responsible for the color of the solution (that was a fine precipitate of your intended product, barium chromate.) Is it possible that your potassium chromate was made using tap water, or that your glassware wasn't cleaned with distilled water prior to use? Barium hydroxide and barium carbonate both give white precipitates that could occur easily from contamination. $\endgroup$– Jason PattersonCommented Sep 29, 2014 at 11:50
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1$\begingroup$ Actually, after some though. Are you sure that your precipitate is white? Could it be that it is white-yellow, but under more deep yellow solution it looks like white? $\endgroup$– permeakraCommented Sep 29, 2014 at 15:28
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1 Answer
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If you used distilled water to prepare the solutions of potassium chromate and barium nitrate, it is more likely that you got a yellow precipitate of $\ce{BaCrO4}$ in a yellow solution of excess $\ce{K2CrO4}$. The yellow color originates from $\ce{CrO4^{2-}}$, and a small amount of finely divided precipitate may look white at first sight (namely when the yellow color of the solution is more intense), when it is actually pale-yellow (it can look like this).
answered Oct 22, 2014 at 18:58