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Two aqueous solutions of urea (molar mass = 60 g/mol ) are prepared. Solution I has a volume of 250 mL and a molarity of 0.4 M . Solution II has a total mass of 106 g . If both solutions contain the exact same mass of urea, what is the molality of Solution II?

Options

  1. A1.00 m
  2. B0.94 m
  3. C0.40 m
  4. D0.10 m

Correct answer

A. 1.00 m

Step-by-step solution

Moles of urea in Solution I = Molarity Volume in L = 0.4 mol/L 0.25 L = 0.1 mol . Mass of urea in Solution I = 0.1 mol 60 g/mol = 6 g . Since Solution II contains the same mass of urea, the mass of urea in Solution II is also 6 g . The total mass of Solution II is given as 106 g . Mass of solvent (water) in Solution II = Mass of solution - Mass of solute = 106 g - 6 g = 100 g = 0.1 kg . Molality of Solution II = Moles of solute Mass of solvent in kg = 0.1 mol 0.1 kg = 1.00 m . Answer: 1.00 m

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