Some Basic Concepts of Chemistry - Result Question 7

####7. 8g of NaOH is dissolved in 18g of H2O. Mole fraction of NaOH in solution and molality (in molkg1 ) of the solution respectively are

(2019 Main, 12 Jan II)

(a) 0.2,11.11

(b) 0.167,22.20

(c) 0.2,22.20

(d) 0.167,11.11

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Solution:

  1. Mole fraction of solute = number of moles of solute + number of moles solvent  number of moles of solute

χSolute =nSolute nSolute +nSolvent =wSolute MwSolute wSolute MwSolute +wSolvent MwSolvent 

Given, wSolute =wNaOH=8g

MwSolute =MwNaOH=40gmol1

wSolvent =wH2O=18g

MwSolvent =18gmol1

χSolute =χNaOH=8/40840+1818=0.20.2+1=0.21.2=0.167

Now, molality (m)= Moles of solute  Mass of solvent (in kg)

=wSolute MwSolute wSolvent ( in g)×1000=84018×1000 =0.218×1000=11.11molkg1

Thus, mole fraction of NaOH in solution and molality of the solution respectively are 0.167 and 11.11molkg1.



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