Experiment 12 PDF

Preview

Summary

Lab Report...

Description

Experiment 12: Molar Mass of a Volatile Liquid

Hypothesis If a sample of an unknown liquid is vaporized, the mass of the vapor can be calculated by knowing the moles of vapor. The physical properties of pressure, volume, and temperature will all be accounted for in van der Waal’s equation.

Materials and Methods Please refer to Experiments 12 on pages 173-180 of Laboratory Manual for Principles of General Chemistry by J. A. Beran (10th Ed.). Deviations from the published procedure are: 1. Only two trials were performed instead of three. Data

Calculations D.3. Molar Mass of compound (g/mol) = [Mass of vapor, mvapor (g)] / [Moles of vapor, nvapor (mol)] = 1.0651 / 0.00893 = 119.27 g/mol D.4. Average Molar Mass (g/mol) = [Molar mass of compound trial 1] + [Molar mass of compound trial 2] /2 = (119.27 + 119.51) /2 = 119.39 g/mol D.5. Standard Deviation of molar mass √(119.39-119.27)2 + (119.39-119.51)2 = 0.1697

D.6. Relative Standard Deviation of molar mass (%RSD) = [Standard Deviation of molar mass] / [Average Molar Mass (g/mol)] * 100 = [0.1697/119.39] *100 = 0.14%

Results

At the end of the experiment, it was possible to determine that the average molar mass of the unknown “Luigi”, was 119.39 g/mol. The standard deviation between the two trials was calculated to be 0.170 and the relative standard deviation of the molar mass was 0.14%. Factors such as atmospheric pressure, volume of the flask, as well as temperature were all known in order to calculate the moles of vapor of the gas. Post-Lab Questions 4. The reported molar mass of the liquid will be unaffected. As per the lab manual, the instructions state that this is okay. However, if the flask was wet, you would need to dry the outside of the flask from any condensed water droplets. 5. The reported mass would be too low if the temperature is misread too high. This is because of the inverse relationship between moles and temperature. If you were to increase the temperature, the moles would decrease, and as a result the molar mass would decrease as well. 6. The calculated molar mass would be too low. Because of this assumption, there would be a decrease in the volume. So, as the volume decreases, the moles calculated would also be too low due to the direct relationship between volume and moles. As a result, if the moles are calculated to be too low, the molar mass would also be calculated too low. 7. Similarly to volume, as the pressure increases, the moles calculated will also increase. So, if the pressure reading on the barometer is too high, the moles would be calculated to be too high, and as a result the molar mass will be too high....