Chemistry 2000, Section A
Spring 1996 Test 2

This exam will be marked out of 100. The detailed breakdown for each question is given in each question. The bonus questions are worth one mark each. Bonus marks will be applied to your final grade, to a maximum of 15/15 for this section of the course (assignment 2 and this test).

1. Here is a portion of the phase diagram of water:

   

   1. What happens to ice heated at a constant pressure lower than the pressure at the triple point? [10 marks]
   2. What can you say about the size of the equilibrium constant for the process inside the solid region of the phase diagram? [10 marks]
   3. Does the boiling temperature of water increase or decrease with pressure? Explain how this information can be obtained from the phase diagram. [10 marks]

   Bonus:

   Why is the triple point useful for calibrating thermometers?

2. Explain what causes the appearance of dew at night. [10 marks]
3. Sketch the ideal cooling curve of a solution. Clearly label the temperature at which freezing starts. Explain the shape of your curve. [20 marks]
4. What is the vapour pressure of a solution prepared by dissolving 10g of sodium fluoride in 100mL of water at C? The molar mass of sodium fluoride is 41.99g/mol. The vapour pressure of pure water at C is 2338Pa, its density is 0.9982g/mL and its molar mass is 18.02g/mol. [20 marks]
5. Suppose that you have an osmometer designed to accurately measure osmotic pressures between 50 and 3000Pa at C. You want to use it to accurately determine the molar mass of a protein whose molar mass you have estimated by other means to be about 100000g/mol. With a molecule this large, you should aim for the lower end of the osmometer's range while leaving yourself a little room for error so you decide on a target osmotic pressure of 100Pa. You will use a 100mL volumetric flask to prepare the aqueous protein solution. How much of the protein should you use for this determination? [20 marks]

   Bonus:

   What are the practical reasons why should you aim for the bottom of the osmometer's working range?