Which of the following compounds will give red colour on Lassaigne test?

Question

Which of the following compounds will give red colour on Lassaigne test? (A) NaCNS (B) NH2CSNH2 (thiourea) (C) NH2CONH2 (urea) (D) p - NH2C6H4SO3H (p -aminobenzene sulphonic acid)

Tardigrade Admin · Accepted Answer

When nitrogen and sulphur both are present in the organic compound, they combine during fusion to form sodium thiocyanate (sulphocyanide). This when heated with

F e S O_{4}

or

F e C l_{3}

, produces a red blood colouration due to ferric thiocyanate (or sulphocyanide). Thus, thiourea and

p

-aminobenzene sulphonic acid give red colour on Lassaigne test.

Q. Which of the following compounds will give red colour on Lassaigne test?

$N a CNS$

$N H_{2} CSN H_{2}$ (thiourea)

$N H_{2} CON H_{2}$ (urea)

$p - N H_{2} C_{6} H_{4} S O_{3} H$ ( $p$ -aminobenzene sulphonic acid)

Q. Which of the following compounds will give red colour on Lassaigne test?

NaCNS

NH2​CSNH2​ (thiourea)

NH2​CONH2​ (urea)

p−NH2​C6​H4​SO3​H (p -aminobenzene sulphonic acid)

$N a CNS$

$N H_{2} CSN H_{2}$ (thiourea)

$N H_{2} CON H_{2}$ (urea)

$p - N H_{2} C_{6} H_{4} S O_{3} H$ ( $p$ -aminobenzene sulphonic acid)