JEE MAIN - Chemistry (2020 - 6th September Morning Slot - No. 2)
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]
[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]
Answer
5
Explanation
Molality of CaCl2 solution = 0.05 m
$$\Delta $$Tb = i Kb m = 3 Ć Kb Ć 0.05 = 0.15 Kb
Molality of CrCl3.xNH3 = 0.10 m
$$\Delta $$Tb' = i Kb $$ \times $$ 0.10
Given, $$\Delta $$Tb' = 2$$\Delta $$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)Clā
i = 3 = 1 + 3 - 6 + x
$$ \Rightarrow $$ x = 5
$$\Delta $$Tb = i Kb m = 3 Ć Kb Ć 0.05 = 0.15 Kb
Molality of CrCl3.xNH3 = 0.10 m
$$\Delta $$Tb' = i Kb $$ \times $$ 0.10
Given, $$\Delta $$Tb' = 2$$\Delta $$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)Clā
i = 3 = 1 + 3 - 6 + x
$$ \Rightarrow $$ x = 5
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