JEE Main 12 Jan 2019 Evening Question 3
Question: 8 g of NaOH is dissolved in 18 g of $ H _2O. $ Mole fraction of $ NaOH $ in solution and molality (in $ mol,k{g^{-1}} $ ) of the solution respectively are [JEE Main Online Paper Held On 12-Jan-2019 Evening]
Options:
A) 0.167, 22.20
B) 0.167, 11.11
C) 0.2, 22.20
D) 0.2, 11.11
Show Answer
Answer:
Correct Answer: B
Solution:
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Mole of $ NaOH=\frac{8}{40}=0.2 $
Mole of water $ =\frac{18}{18}=1 $
Total moles $ =1+0.2=1.2 $
Mole fraction of $ NaOH $ $ =\frac{Moles\ of\ NaOH}{Total\ moles}=\frac{0.2}{1.2}=0.167$
$ Molality=\frac{Moles\ of\ NaOH}{Mass\ of\ solvent}\times 1000 $ $ =\frac{0.2}{18}\times 1000=11.11m $
