KVPY Sample Paper KVPY Stream-SX Model Paper-15

The elevation in boiling point, when 13.44 g of freshly prepared \[CuC{{l}_{2}}\]are added to one kilogram of water, is [Some useful data, \[{{K}_{b}}=0.52K\,kg\,mo{{l}^{-1}},\]molecular weight of \[CuC{{l}_{2}}=134.4\,g].\]

A) 0.05

B) 0.1

C) 0.16

D) 0.21

Correct Answer: C

Solution :

Given, weight of \[CuC{{l}_{2}}=13.44g\]

Molecular weight of \[CuC{{l}_{2}}=13.44g\]

\[\text{Molality}=\frac{\text{Number}\,\text{of}\,\text{moles}\,\text{of}\,\text{solute}}{\text{Mass}\,\text{of}\,\text{solvent}\,\text{(kg)}}\]

\[\because \]No. of moles of solute, \[CuC{{l}_{2}}=\frac{13.44}{134.1}\]?

\[\therefore \] Molality \[=\frac{\frac{13.44}{134.1}}{1}=0.1\]

Now, \[CuC{{l}_{2}}\underbrace{C{{u}^{2+}}+2C{{l}^{-}}}_{3particles}\]

\[\therefore \]\[i=3\]

\[\Rightarrow \]\[\Delta {{T}_{b}}=i{{K}_{b}}\cdot m=3\times 0.52\times 0.1\]

\[=0.156\approx 0.16\]