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 $Q$ .

Q1. The number of moles of potassium iodide required to produce two moles of $P$ is ______.

Your answer

Solution

Potassium ferricyanide $K_{3} [F e (C N)_{6}]$ contains $F e^{3 +}$ and acts as a mild oxidising agent. It oxidises iodide to iodine while itself being reduced to potassium ferrocyanide $K_{4} [F e (C N)_{6}]$ (this is the complex $P$ ). The balanced redox equation:

$2 K I + 2 K_{3} [F e (C N)_{6}] ⟶ I_{2} + 2 K_{4} [F e (C N)_{6}] .$

The stoichiometry shows $2$ moles of $K I$ produce $2$ moles of $K_{4} [F e (C N)_{6}]$ ( $P$ ).

$∴$ Moles of $K I$ required = $2.$

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