MCQ
Match the organic compounds in column $-I$ with the Lassaigne's test results in column $-II$ appropriately
Column $-I$ Column $-II$
$(A)$ Aniline $(i)$ Red colour with $FeCl_3$
$(B)$ Benzene sulfonic acid $(ii)$ Violet colour with sodium nitroprusside
$(C)$ Thiourea $(iii)$ Blue colour with hot and acidic solution of $FeSO_ 4$
  • A
    $A - (ii); B - (iii) ; C - (i)$
  • B
    $A - (iii); B - (i) ; C - (ii)$
  • $A - (iii); B - (ii) ; C - (i)$
  • D
    $A - (ii); B - (i) ; C - (iii)$

Answer

Correct option: C.
$A - (iii); B - (ii) ; C - (i)$
c
$(c)$ In Lassaigne's test, fusion with sodium take place and following species formed respectively.

$(a)$ Aniline $\to $ $CN^-$

$(b)$ Benzene sulfonic acid $\to $ (figure)

$(c)$ Thiourea $\to $ $S^{2-}$

Reaction of $CN^-$ with hot and acidic solution of $FeSO_4$ lead to formation of $Fe_4[Fe(CN)_6]_3$ which is blue in colour. It contains iron in both $II$ and $III$ oxidation state.

Reaction of $S^{2-}$ with sodium nitroprusside

$N{a_2}S + N{a_2}[Fe{(CN)_5}NO] \to \mathop {N{a_4}[Fe{{(CN)}_5}NOS]}\limits_{(violet\,in\,colour)} $

Phenoxide ion on reacting with $FeCl_3$ give red colour with $FeCl_3$.

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