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Question

Mole fraction of A in H2O is 0.2 the molality of A in H2O is:


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Solution

Step 1: Find mole fraction of B.

  • We are given that Mole fraction of A is 0.2, which means that 0.2 moles of A is present in one mole of solution.
  • Mole fraction of B is:
    1-XA=1-0.2=0.8
  • This means that 0.8 moles of B is present in one mole of solution.

Step 2: Calculate mass of water

  • To calculate the mass of water, we use the equation:
    Numberofmoles=GivenmassMolarmass
  • Moles of water =0.8
  • The molar mass of water 18gmol-1
  • Putting values in the above equation, we get:
    0.8=Mass of water18gmol-1
  • So, the Mass of water 14.4g

Step 3: Calculate molality of A in Water

  • To calculate the molality, we use the equation:
    Molality=Moles of soluteMass of solvent(kg)
  • We are given:
    Moles of solute =0.2mol
    Mass of solvent (water) =14.4g=0.0144kg
  • Putting values in above equation, we get:

Molality=0.2mole0.0144kg=13.88molkg-1


Hence, the molality of the A in water is 13.88molkg-1


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