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I was testing an organic dye for nitrogen today in lab.

First I added powdered ferrous sulfate (.2 g) and the mixture gave prussian blue precipitate. Then I boiled and cooled it. When I acidified the mixture using diluted sulfuric acid, the mixture cleared and only a few small blue crystals remained, when there should've been a bluish-green precipitate, ensuring the presence of nitrogen(organic dyes should contain nitrogen).

Where did it go wrong?

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    $\begingroup$ Did you google "Lassaigne's nitrogen" ? The test seems quite different than what you did. $\endgroup$ – MaxW Mar 28 '16 at 21:25
  • $\begingroup$ Not all organic dies include nitrogen. It's helpful, for sure, but not a rule. It sounds like this one does, though. However, MaxW is right. $\endgroup$ – SendersReagent Mar 28 '16 at 22:18
  • $\begingroup$ thanks MaxW for your reply.I did look 'lassaigne's nitrogen test' and it does seem like I was doing this test differently. but that's how we were taught to do the nitrogen detection test.I did the same test on several other compounds containing nitrogen and it gave positive results. I never added ferrous chloride in any of those test yet it showed positive results.that's why I can't be sure if I was doing the test wrong $\endgroup$ – sajjad islam Mar 30 '16 at 14:42

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