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

1. 5.00
2. 5.00
3. 5.00
4. 5.00

Correct answer: 5.00

Solution

The elevation of boiling point is directly proportional to the molality of the solution and the number of particles produced upon dissociation. Since CrCl₃ dissociates into four ions (one Cr³⁺ and three Cl⁻) and the ammonia molecules are included in the coordination sphere, the effective particle concentration for the CrCl₃ solution is higher than that of CaCl₂, which dissociates into three ions. Given the relationship between the boiling point elevation and the molality, the value of x must be 5 to balance the effect of the different ion contributions.

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