JEE Advanced 2024 — Paper 2 — CHEM-IV solution

JEE Advanced2024Paper 2CHEM-IV

PARAGRAPH II

When potassium iodide is added to an aqueous solution of potassium ferricyanide, a reversible reaction is observed in which a complex $P$ is formed. In a strong acidic medium, the equilibrium shifts completely towards $P$ . Addition of zinc chloride to $P$ in a slightly acidic medium results in a sparingly soluble complex $Q$ .

Q2. The number of zinc ions present in the molecular formula of $Q$ is _____.

Your answer

Solution

$P$ is potassium ferrocyanide $K_{4} [F e (C N)_{6}]$ . Addition of zinc chloride in slightly acidic medium precipitates the mixed potassium-zinc ferrocyanide:

$2 K_{4} [F e (C N)_{6}] + 3 Z n C l_{2} ⟶ K_{2} Z n_{3} [F e (C N)_{6}]_{2} (sparingly soluble) + 6 K C l .$

The molecular formula of the sparingly soluble complex $Q$ is $K_{2} Z n_{3} [F e (C N)_{6}]_{2}$ , which contains $3$ zinc ions per formula unit.

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