Verified Solution • 2025–26 Session moderate

QJEEM20Ch7199: JEE Main 2020 Chemistry - Class 12 JEEM20Ch7199 Solution: The elevation of boiling point of 0.10 m aqueous CrCl 3 .xNH 3…

The elevation of boiling point of 0.10 m aqueous CrCl3.xNH3 solution is two times that of 0.05 m aqueous CaCl2 solution. The value of x is ______.

[Assume 100% ionisation of the complex and CaCl2, coordination number of Cr as 6, and that all NH3 molecules are present inside the coordination sphere]

Step-by-Step Verified Solution

Molality of CaCl2 solution = 0.05 m

Δ\Delta Tb = i Kb m = 3 × Kb × 0.05 = 0.15 Kb

Molality of CrCl3.xNH3 = 0.10 m

Δ\Delta Tb' = i Kb ×\times 0.10

Given, Δ\Delta Tb' = 2 Δ\Delta Tb

⇒\Rightarrow i Kb ×\times 0.10 = 0.15 Kb

⇒\Rightarrow i = 3

Co-ordination number of Cr is 6.

[Cr(NH3 )x.Cl6-x]Cl3-6+x →\to [Cr(NH3 )xCl] + (3-6+x)Cl–

i = 3 = 1 + 3 - 6 + x

⇒\Rightarrow x = 5

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