Question

The mole fraction of a certain nonelectrolyte compound in a solution containing only that substance and water is 0.100. The molecular weight of water is 18.0 g/mol. What additional information is needed to determine the molality of the solution?

1.) The molecular weight of the compound.

2.) The density of the solution.

3.) The density of the solute.

4.) No additional information; the molality can be calculated from the information given.

5.) The mole fraction of water in the solution.

Answer 1

if X₁ is the mole fraction of solute And X₂ is the mole fraction of the solvent then we know

X₁ + X₂ = 1

In question mole fraction of the solute is given as 0.100 so mole fraction of solvent is = 1 - 0.100 = 0.9

Again Molality formula is =

=   

=

= as we know no of moles (n) = weight (w)/ molecular mass (m)

=    and so

= [ where n₁ is no of moles of solute and

= 6.172 m and n₂ is no of moles of solvent]

as X₁ and X₂ are known and molecular weight of water that is solvent is known Molality can be calculated no additional information is needed