Week 1 DB

Experiment 27           Name: Karen Ramirez Pre laboratory Problems   What are the four colligative properties? Four colligative properties are boiling point, vapor pressure, osmotic pressure, and freezing point.  What are the melting point and freezing point of cyclohexane? Cyclohexane has a freezing point of 6.50 degrees Celsius and a melting point of 7 degrees Celsius. A 0.500 g sample of unknown substance is determined to be 0.002272 moles, what is the molar mass of the substance? 0.500/0.002272 The molar mass of the substance is 220.07 MM What is the freezing point of the pure solvent and the mixture in Figures 4 and 5? The freezing point in figure 4 is 28 degrees Celsius.  In figure 5 the freezing point is 20 degrees Celsius. Benzene (C6H6) melts at 5.5°C.  If 1.50 grams of naphthalene (C10H8) is added to 25.00 g of benzene, what will the melting point of the solution be? The melting point of the solution would be 1.06 degrees Celsius and I used T=kb*m. The freezing point depression constant of acetic acid is 3.90°C kg/mol.   Addition of 0.100 g of an unknown compound to 2.50 g of acetic acid results in a decrease in the melting point of 2.3°C. What is the molar mass of the unknown? The molar mass of the unknown substance is 32.3 g/mol. Where us used the (m) of the solution and found the mols and then converted to grams (MM). Considering the other methods you may have used that could be used to determine molecular mass such as titration, quantitative precipitation or even pressure temperature data, explain when the melting point depression method should be used?  The melting point method would be used when figuring out if the substance that is being used pure or not.