The Molar Mass of a Volatile Liquid Adam Kozdrowicz Adam Li 11/05/12 Mr. McCready Purpose: The purpose of this procedure is to determine the molar mass of an unknown liquid, evaporate a sample of a liquid substance, and measure certain physical properties of the substance as it condenses. Procedure: 1. Obtain safety goggles. 2. Trim a piece of aluminum foil so that it covers the top of a small 13 x 100 mm test tube. Secure the foil with electrical tape. Make sure that the electrical tape is tightly stretched around the foil so that water doesn’t get underneath it.
. Make a small, needle-sized hole in the top of the tinfoil. 4. Use a sensitive balance to measure the mass of the empty test tube and foil. 5. Fill a 400mL beaker up with around 300mL of tap water, and keep this beaker on a hot plate that is set to around 370K. Keep track of the temperature with a temperature probe. 6. Fill a second 400mL beaker up with around 300mL of cold tap water.
7. Obtain a liquid sample of an unknown volatile compound. Pour around 0. 5mL of the liquid into the test tube through the needle sized hole in the tinfoil. 8.
Place the test tube with the liquid in the beaker that is on the hot plate, and be mindful not to let it touch the temperature probe that is measuring the temperature of the water. Also make sure to immerse as much of the test tube in the water as possible without getting the electrical tape or foil wet. 9. Heat the test tube in the water until there is no more liquid left in the tube. Then, wait two more minutes to make sure that all of the liquid has evaporated. 10. Take out the test tube and inject another sample around 0. 5mL of the unknown volatile compound and place it back into the heated water. 1. Wait until all of the liquid has evaporated, and then wait two more minutes to be sure. 12. Take out the test tube and place it into the beaker with cold water. Wait until a liquid condenses within the test tube. 13. Weigh the test tube and the liquid’s mass on a sensitive balance and record it. 14. Repeat steps 10-13 until your results keep yielding numbers that are very close to one another. Record these numbers. 15. Record the room barometric pressure. 16. Completely rinse out the test tube and fill it to the top with tap water. Measure and record the mass of the test tube, water, and foil.
Data: Trail 1Trail 2 Mass of test tube and foil cover (grams)19. 312 19. 424 Temperature of water bath (Kelvin)368. 0368. 0 Mass of test tube, foil, and gas sample (grams)19. 39419. 426 Barometric Pressure (atm)0. 9970. 997 Mass of test tube, foil, and water (grams)40. 45540. 455 Observations: •The tape seemed to be water logged. •The numbers from our first trial and second trial varied greatly. Results: The Molar Mass of the unknown volatile liquid was calculated to be 120g/mol. The liquid was Acetone, which has a molar mass of 58g/mol. Our results were inaccurate.
Questions: 1. See Calculations 2. See Calculations 3. See Calculations 4. The unknown liquid substance was identified to be Acetone. 5. I used a variation of the ideal gas law to calculate the molar mass. The variation of the ideal gas law was mm = gRT/PV 6. No, the vapor molecules were attracted to one another and thus the actual volume was smaller than the measured volume. 7. If not all of the vapors had been condensed, the mass of the test tube and the vapors would have been measured to be lighter than they really were. 8. My experiment would not have been affected.
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