Solutions Question 354
Question: A solution containing 1.8 g of a compound (empirical formula $ CH_2O $ ) in 40 g of water is observed to freeze at $ -0.465{}^\circ C $ . The molecular formula of the compound is ( $ K_{f} $ of water $ =1.86kgKmo{l^{-1}} $ )
Options:
A) $ C_2H_4O_2 $
B) $ C_3H_6O_3 $
C) $ C_4H_8O_4 $
D) $ C_6H_{12}O_6 $
Show Answer
Answer:
Correct Answer: D
Solution:
$ \Delta T_{f}=K_{f}\times m $
$ M=\frac{1000\times K_{f}\times w_2( solute )}{\Delta T_{f}\times w_1( solvent )} $
$ =\frac{1000\times 1.86\times 1.8}{0.465\times 40}\Rightarrow M=180 $ Molecular formula = $ {{(empiricalformulae)}_{n}} $
$ n=\frac{Molecularmass}{Empiricalformulamass}=\frac{180g}{30}=6 $ Molecular formula $ ={{(CH_2O)} _6}=C_6H _{12}O_6 $
