JEE Main 2025 Apr 2 Shift 1, Chemistry Q16: Principles Of Qualitative Analysis

JEE Main2025Apr 2, Shift 1Chemistry

Choose the correct tests with respective observations.

(A) $C u S O_{4}$ (acidified with acetic acid) + $K_{4} [F e (C N)_{6}] \to$ Chocolate brown precipitate.

(B) $F e C l_{3} + K_{4} [F e (C N)_{6}] \to$ Prussian blue precipitate.

(D) $M g C l_{2} + K_{4} [F e (C N)_{6}] \to$ Blue precipitate.

(E) $B a C l_{2} + K_{4} [F e (C N)_{6}]$ , neutralised with NaOH $\to$ White precipitate.

Choose the correct answer from the options given below :

Solution

Reviewing each precipitation reaction with potassium ferrocyanide:

(A) In an acetic-acid medium, $C u^{2 +}$ gives the characteristic chocolate-brown $C u_{2} [F e (C N)_{6}]$ :

$2 C u S O_{4} + K_{4} [F e (C N)_{6}] C H_{3} C O O H C u_{2} [F e (C N)_{6}] + 2 K_{2} S O_{4} ✓$

(B) Ferric ions form ferric ferrocyanide, the classic Prussian blue:

$4 F e C l_{3} + 3 K_{4} [F e (C N)_{6}] \to F e_{4} [F e (C N)_{6}]_{3} + 12 K C l ✓$

(C) In an ammoniacal medium, $Z n^{2 +}$ gives a white-to-bluish-white $K_{2} Z n_{3} [F e (C N)_{6}]_{2}$ :

$3 Z n C l_{2} + 2 K_{4} [F e (C N)_{6}] N H_{4} O H K_{2} Z n_{3} [F e (C N)_{6}]_{2} + 6 K C l ✓$

(D) $M g^{2 +}$ does not give a blue precipitate with ferrocyanide; the description is wrong. ✗

(E) $B a C l_{2}$ does not respond to this test in the manner described, and ferrocyanide itself decomposes in NaOH; the observation is wrong. ✗

$∴$ The correct observations are A, B and C; option (3) is correct.

Concept behind this question

Concept-wise practice with instant solutions on Fundamenthol.