Solutions Question 353
Question: The difference between the boiling point and freezing point of an aqueous solution containing sucrose (molecular $ wt=342gmol{e^{-1}} $ ) in 100 g of water is $ 105{}^\circ C $ . If $ K_{f} $ and $ K_{b} $ of water are 1.86 and $ 0.51Kkgmo{l^{-1}} $ respectively, the weight of sucrose in the solution is about
Options:
A) 34.2 g
B) 342 g
C) 7.2 g
D) 72 g
Show Answer
Answer:
Correct Answer: D
Solution:
$ (100+\Delta T_{b})-(0-\Delta T_{f})=105 $
$ \Delta T_{b}+\Delta T_{f}=5 $
$ m( K_{b}+K_{f} )=5 $
$ m=\frac{5}{2.37} $ i.e., $ \frac{5}{2.37} $ moles in 1000 g water (or) $ \frac{5}{2.37\times 10} $ moles in 100 g water
$ \therefore $ Wt. of sucrose $ =\frac{5}{2.37\times 10}\times 342=72g $
