Chemistry · Different methods for expressing the concentration of solution: molality, molarity, mole fraction, percentage (by volume and mass both)

What should be the density of an aqueous solution of urea \) such that the molar

What should be the density of an aqueous solution of urea \( (\text {molarmass}=\mathbf{6 0} \boldsymbol{g} / \text { mol}) \) such that the molarity and molarity of the solution become equal?

  • A. \( 16.0 g / m l \)
  • B. \( 1.6 g / m l \)
  • C. \( 1.06 g / m l \)
  • D. \( 1.16 g / m l \)

Step-by-step solution

Molarity (M) and molality (m) are equal when the volume of solution (in liters) equals the mass of solvent (in kg). For a solution with 1 kg solvent, moles of solute n = m; volume = n/M = 1 L. Mass of solute = n × 60 g, total mass = 60n + 1000 g, volume = 1000 mL. Density = (60n + 1000)/1000 = 1 + 0.06n. Setting n = 1 (typical 1 M solution) gives density = 1.06 g/mL. Thus, for a 1 M solution, M = m, and density is 1.06 g/mL.
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