question_answer

The boiling point elevation constant for benzene is \[2.57{}^\circ C/m.\] The boiling point of benzene is \[81{}^\circ C\]. Determine the boiling point of solution formed when 10 g of \[{{C}_{4}}{{H}_{12}}\]is dissolved in 20 g benzene.

A) 71.46   

B) 7.14

C) 85.76   

D) 88.14   

Correct Answer: D

Solution :

[d] \[\Delta T={{k}_{b}}\cdot m\] \[={{k}_{b}}\cdot \frac{{{W}_{B}}}{{{M}_{{{W}_{B}}}}}\times \frac{1000}{{{W}_{A}}}\] \[=2.57\times \frac{10}{180}\times \frac{1000}{20}\] \[={{7.14}^{0}}C\] Now, \[\Delta T={{T}_{b}}-{{T}_{b}}^{0}\] \[\Rightarrow {{T}_{b}}=\Delta {{T}_{b}}+{{T}_{b}}^{0}\] \[=7.14+81=88.14{}^\circ C\]