Q. $\mathrm{CrCl_3\cdot xNH_3}$ can exist as a complex. 0.1 molal aqueous solution of this complex shows a depression in freezing point of $0.558^\circ$C. Assuming 100% ionisation of this complex and coordination number of Cr is 6, the complex will be (Given $K_f=1.86\ \mathrm{K\,kg\,mol^{-1}}$)

A) [Cr(NH₃)₅Cl]Cl₂
B) [Cr(NH₃)₆]Cl₃
C) [Cr(NH₃)₃Cl₃]
D) [Cr(NH₃)₄Cl₂]Cl
Explanation

[Solution by Dr. Abubacker] $\Delta T_f=iK_fm\Rightarrow i=\frac{0.558}{1.86\times0.1}=3$. Three particles per formula unit means one complex ion and two free chloride ions: $[\mathrm{Cr(NH_3)_5Cl}]\mathrm{Cl_2}$ (coordination number 6). Answer (1).

Dr. Abubacker
Reviewed by Dr. Abubacker

Physics Educator & NEET/JEE Specialist

Ph.D. in Physics with 19+ years of teaching experience.

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