Data Analysis
Table 1: Freezing Point Depression Measurement Calculations
| Parameter | Trial 1 | Trial 2 |
| Mass of the lauric acid (g) | 8.1877 | 8.1877 |
| Mass of the unknown sample (g) | 0.5188 | 1.0558 |
| Freezing point of lauric acid (degrees C) | 43.5 | 43.5 |
| Freezing point of lauric acid mixed with the unknown solute (degrees C) | 41.1 | 39.3 |
| Change in freezing point (degrees C) | 2.4 | 4.2 |
| Molar mass (experimental) of unknown solute (g/mol) | 117.67 | 119.74 |
| Molality of the solution (mol/kg) | 0.0538 | 1.077 |
| Moles of the unknown sample (mol) | 0.004409 | 0.008817 |
| Possible solute | Benzoic Acid | Benzoic Acid |
| Molar Mass of possible solute (g/mol) | 122.4 | 122.4 |
| Percent error | -3.864 | -2.173 |
Figure 1: Temperature vs Time
Calculations
1.Calculate the formula weight of the solute.
Trial 1
Trial 2
2. Calculate the number of moles of the solute used. Then calculate the molality of the solution.
Trial 1
Trial 2
3. Percent Error
Trial 1
Trial 2
Conclusion
The purpose of this lab was to determine the molecular mass of a compound by measuring the freezing point depression. In this experiment the freezing point of a pure solvent, lauric acid was measured by melting and then freezing it. Then the freezing point of the mixture of lauric acid and an unknown solute was determined. The difference between the freezing point of the solution and the freezing point of pure lauric acid was the freezing point depression of the unknown solute. From this freezing point change, the formula weight of the solute was calculated. Based on the calculation of the molar mass, the unknown solute #1 was Benzoic acid. The actual formula weight of Benzoic acid is 122.4 g/mol. The experimental value of the molar mass of Benzoic acid was on average, 118.705 g/mol. The percent error of the experiment was about -3.287% which means the results are pretty accurate. Some possible errors of this experiment could have been from not transferring all of the unknown solute from the weighing dish to the test tube and some of the solute could have been stuck to the top sides of the test tube while stirring the solution.