JEE Main 2025 Jan 24 Shift 2, Chemistry Q12: Colour, Magnetism And Stability Of Co-ordination Compounds

JEE Main2025Jan 24, Shift 2Chemistry

When Ethane-1,2-diamine is added progressively to an aqueous solution of Nickel (II) chloride, the sequence of colour change observed will be :

A
Pale Blue $\to$ Blue $\to$ Green $\to$ Violet
B
Pale Blue $\to$ Blue $\to$ Violet $\to$ Green
C
Green $\to$ Pale Blue $\to$ Blue $\to$ Violet
D
Violet $\to$ Blue $\to$ Pale Blue $\to$ Green

Solution

$N i C l_{2}$ in water exists as the hexaaqua complex $[N i (H_{2} O)_{6}]^{2 +}$ , which is green. Stepwise replacement of water by the bidentate ligand ethane-1,2-diamine (en) shifts the d-d absorption to higher energy because en is a stronger-field ligand than $H_{2} O$ , so the complementary colour shifts from green to blue and finally to violet.

$[N i (H_{2} O)_{6}]^{2 +} (green) + e n [N i (H_{2} O)_{4} (e n)]^{2 +} (pale blue)$

$+ e n [N i (H_{2} O)_{2} (e n)_{2}]^{2 +} (blue) + e n [N i (e n)_{3}]^{2 +} (violet)$

Sequence: Green $\to$ Pale Blue $\to$ Blue $\to$ Violet.

Correct option: (3)

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JEE Main 2025 Jan 24 Shift 2, Chemistry Q12: Colour, Magnetism And Stability Of Co-ordination Compounds

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