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Some Basic Concepts of Chemistry question

2019 · 12 Jan · Shift 2 · Q12
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Some Basic Concepts of Chemistry question

2019 · 12 Jan · Shift 2 · Q12

JEE MainChemistrySome Basic Concepts of ChemistryMCQ+4 / −1
8 g of NaOHNaOHNaOH is dissolved in 18g of H2OH_2OH2​O. Mole fraction of NaOHNaOHNaOH in solution and molality (in mol kg–1) of the solution respectively are -
  1. A
    0.2, 11.11
  2. B
    0.167, 22.20
  3. C
    0.167, 11.11
  4. D
    0.2, 22.20
View written solutionFree

Correct answer: C

  1. Calculate moles of each component

  • For NaOHNaOHNaOH: MNaOH=23+16+1=40 g mol−1M_{NaOH} = 23 + 16 + 1 = 40\ \text{g mol}^{-1}MNaOH​=23+16+1=40 g mol−1 nNaOH=840=0.2 moln_{NaOH} = \frac{8}{40} = 0.2\ \text{mol}nNaOH​=408​=0.2 mol

  • For H2OH_2OH2​O: MH2O=18 g mol−1M_{H_2O} = 18\ \text{g mol}^{-1}MH2​O​=18 g mol−1 nH2O=1818=1 moln_{H_2O} = \frac{18}{18} = 1\ \text{mol}nH2​O​=1818​=1 mol

  1. Find mole fraction of NaOHNaOHNaOH

Total moles in solution: ntotal=0.2+1=1.2n_{\text{total}} = 0.2 + 1 = 1.2ntotal​=0.2+1=1.2

Mole fraction of NaOHNaOHNaOH: xNaOH=0.21.2=16=0.167x_{NaOH} = \frac{0.2}{1.2} = \frac{1}{6} = 0.167xNaOH​=1.20.2​=61​=0.167

  1. Find molality of the solution

Molality is defined as: m=moles of solutemass of solvent in kgm = \frac{\text{moles of solute}}{\text{mass of solvent in kg}}m=mass of solvent in kgmoles of solute​

Here,

  • moles of solute =0.2= 0.2=0.2 mol
  • mass of solvent =18= 18=18 g =0.018= 0.018=0.018 kg

So, m=0.20.018=11.11 mol kg−1m = \frac{0.2}{0.018} = 11.11\ \text{mol kg}^{-1}m=0.0180.2​=11.11 mol kg−1

  1. Match with the options

The required pair is: 0.167, 11.110.167,\ 11.110.167, 11.11

This matches Option C.

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