Colligative Properties Worksheet

Complete the following questions and problems relating to colligative properties.

1) Write the mathematical expression for boiling point elevation. Define all of the terms used.

2) Write the mathematical expression for freezing point depression. Define all of the terms used.

3) When sugar is dissolved in water, will the resulting solution boil at a higher or lower temperature than pure water? Explain.

4) When salt is dissolved in water, will the resulting solution freeze at a higher or lower temperature than pure water? Explain.

5) What is the change in boiling point (vs. pure water) of a 1.25 molal solution of o sugar in water? The Kb for water is 0.52 C/m. Assume i = 1. 6) What is the change in freezing point (vs. pure water) of a 0.78 molal solution o of NaCl in water? The Kf for water is 1.86 C/m. Assume i = 2 for NaCl.

7) A solution was prepared by dissolving 0.42 mol hexane into 500g CCl4. What is the change in freezing point (vs. pure CCl4) of this solution? The Kf for CCl4 is 30.0oC/m. Assume i = 1 for hexane.

8) A solution was prepared by dissolving 0.16 mol ethanol into 750g ether. What is the change in boiling point (vs. pure ether) of this solution? The K b for ether is 2.02oC/m. Assume i = 1 for ethanol.

9) A solution of propylene glycol (antifreeze) in your car’s radiator has a freezing o o point of –20 C. What is the molality of the solution? Kf for water is 1.86 C/m. Assume i = 1 for propylene glycol. 10) In order to make spaghetti cook faster, a chef adds salt to water. How many moles of salt would he need to add to 1.0 kg water to make the water boil at o o 105 C? The Kb for water is 0.25 C/m. Assume i = 2 for NaCl.

11) How many grams of NaCl would the chef in problem 10 need to add?