Determination of Molecular Masses — Prelims Questions

A solution prepared by dissolving $1.25,\text{g}$ of a non-electrolyte in $50,\text{mL}$ of water at $27^circ\text{C}$ has an osmotic pressure of $2.5,\text{atm}$. Assuming the density of the solution is $1.0,\text{g/mL}$, what is the molecular mass of the solute? (Given: $R = 0.0821,\text{L atm mol}^{-1}\text{K}^{-1}$)

Which of the following colligative properties is most suitable for determining the molecular mass of a high molecular weight polymer that is sensitive to temperature changes?

A $0.1,\text{M}$ aqueous solution of $ext{CaCl}_2$ has a freezing point depression of $0.558^circ\text{C}$. Given $K_f$ for water is $1.86,\text{K kg mol}^{-1}$, calculate the van't Hoff factor ($i$) for $ext{CaCl}_2$ in this solution.

A $1.0,\text{g}$ sample of a non-volatile, non-electrolyte solute is dissolved in $100,\text{g}$ of benzene. The freezing point of the solution is $5.0^circ\text{C}$. The freezing point of pure benzene is $5.5^circ\text{C}$ and its $K_f$ is $5.12,\text{K kg mol}^{-1}$. What is the molecular mass of the solute?

An aqueous solution containing $1.0,\text{g}$ of urea (molecular mass $60,\text{g/mol}$) in $100,\text{g}$ of water boils at $100.18^circ\text{C}$. If $K_b$ for water is $0.52,\text{K kg mol}^{-1}$, what is the observed elevation in boiling point for this solution?

Which of the following statements is INCORRECT regarding the determination of molecular masses using colligative properties?

A solution of a non-volatile solute in water has a boiling point of $100.10^circ\text{C}$. If the molal elevation constant ($K_b$) for water is $0.52,\text{K kg mol}^{-1}$, what is the molality of the solution?