JEE Advanced · 2009 · 12 Apr 2009 · Paper 1 · Compounds Containing Nitrogen

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p

-Amino-

N, N

-dimethylaniline is added to a strongly acidic solution of

X

. The resulting solution is treated with a few drops of aqueous solution of

Y

to yield blue coloration due to the formation of methylene blue. Treatment of the aqueous solution of

Y

with the reagent potassium hexacyanoferrate(II) leads to the formation of an intense blue precipitate. The precipitate dissolves on excess addition of the reagent. Similarly, treatment of the solution of

Y

with the solution of potassium hexacyanoferrate(III) leads to a brown coloration due to the formation of Z.

The compound

X

(A) $NaNO_{3}$
(B) $NaCl$
(C) $Na_{2} SO_{4}$
(D) $Na_{2} S$ ✓ Correct

Answer: (D)

Solution

The formation of methylene blue requires

H_{2} S

in acidic solution. The compound

X

that produces

H_{2} S

in strongly acidic solution is

Na_{2} S

Na_{2} S + 2 H^{+} \to H_{2} S + 2 Na^{+}

The

H_{2} S

then reacts with

p

-amino-

N, N

-dimethylaniline to form methylene blue.

Therefore, the answer is **(D)

Na_{2} S

**.

JEE Advanced · 2009 · 12 Apr 2009 · Paper 1 · Single correct option

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JEE Advanced · 2009 · 12 Apr 2009 · Paper 1 · Compounds Containing Nitrogen

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