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Practical Organic Chemistry question

2022 · 26 Jun · Shift 1 · Q6
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Practical Organic Chemistry question

2022 · 26 Jun · Shift 1 · Q6

JEE MainChemistryPractical Organic ChemistryMCQ+4 / −1
Given below are two statements : Statement I : In 'Lassaigne's Test', when both nitrogen and sulphur are present in an organic compound, sodium thiocyanate is formed. Statement II : If both nitrogen and sulphur are present in an organic compound, then the excess of sodium used in sodium fusion will decompose the sodium thiocyanate formed to give NaCNNaCNNaCN and Na2SNa_2SNa2​S. In the light of the above statements, choose the most appropriate answer from the options given below :
  1. A
    Both Statement I and Statement II are correct.
  2. B
    Both Statement I and Statement II are incorrect.
  3. C
    Statement I is correct but Statement II is incorrect.
  4. D
    Statement I is incorrect but Statement II is correct.
View written solutionFree

Correct answer: A

  1. Recall Lassaigne's test when N and S are both present

    In sodium fusion, elements of the organic compound are converted into ionic salts.

    • If only nitrogen is present: Na+C+N→NaCNNa + C + N \rightarrow NaCNNa+C+N→NaCN
    • If only sulphur is present: 2Na+S→Na2S2Na + S \rightarrow Na_2S2Na+S→Na2​S
    • If both nitrogen and sulphur are present together, they combine during fusion to form: Na+C+N+S→NaSCNNa + C + N + S \rightarrow NaSCNNa+C+N+S→NaSCN

    Thus, Statement I is correct: sodium thiocyanate, NaSCNNaSCNNaSCN, is formed.

  2. Check the effect of excess sodium

    In Lassaigne's test, if excess sodium is used, the sodium thiocyanate formed can decompose as: NaSCN+2Na→NaCN+Na2SNaSCN + 2Na \rightarrow NaCN + Na_2SNaSCN+2Na→NaCN+Na2​S

    Therefore, when excess sodium is present, thiocyanate gets converted into sodium cyanide and sodium sulphide.

    Hence, Statement II is also correct.

  3. Conclusion

    • Statement I: Correct
    • Statement II: Correct

    Therefore, the correct option is: A\boxed{A}A​

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