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Partners: Jeff Somvorachith 
 11. Molecular Mass Determination Using Boiling and Freezing Point 
 Purpose:  
 To practice calculating the molecular mass of solutes by comparing boiling and freezing point of two solutes with known concentrations. 
 Procedure: 
 A.  
 
 
 
 
 
 Measure 50g of distilled water into a 125ml flask. set up the flask on a hot plate and hang a thermometer in the flask using a clamp, not letting the thermometer touch the flask. Record the temperature to the nearest 0.5  o C after heated. 
 Prepare a solution of 10g potassium nitrate in 50g of distilled water. Determine the boiling point of the solution using the equation m=ΔT BP /K BP where K BP =0.512 o C, m=molality, and ΔT=change in temperature. Dispose of the solution by rinsing it down a sink. 
 Repeat step 2, but replace the KNO 3 with C6H12O 6 , Dextrose. 
 
 
 
 
 
 B.  
 
 
 
 
 
 Dissolve 5g of KNO 3 in 50g of water in a 125ml flask. Place the flask in a beaker with rock salt, with the beaker wrapped in a paper towel. Wait until crystals form in the solution and becomes slushy. Record the temperature. Rinse the solution down a drain. 
 Dissolve 10g C 6 H 12 O 6 in 50g of distilled water. Place the flask with the solution in a beaker filled with ice an rock salt and wait until the solution crystalizes. Measure the temperature and rinse down a drain.