Wednesday, 21 September 2016

Why dil HNO3 is added to the sodium extract before detection of halogen in organic compounds.

1       Why dil HNO3 is added to the sodium extract before detection of halogen in organic compounds.

Ans;  A few drops of HNO3 is added to lassaigne,s solution and then boil . It is for the removing of any CN- or S-2 ions in the form of HCN and H2S.
As HCN and H2S are very weak acids and ionize to a very small extent,
CN- + H+  → HCN
S-2 + 2H+  → H2S

Therefore when silver nitrate is added for the detection of  halogen. Only AgX will be precipitated and will have no precipitate of AgCN or Ag2S
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2 comments:

  1. alfachemistry30 August 2018 at 09:42

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  2. Eleonore11 February 2019 at 12:34

    Hello, I would like to know the concentration for the HNO3 that is needed for the detection test of halogen. Thank you !

    ReplyDelete