Determining Molar Mass by Ideal Gas Law

I. abstractionist By manipulating the ideal gas law (PV=nRT), we provide be find the seawallar tidy sum of an unknown volatile crystalline. Heating a flaskfulful alter with an unknown, easily evaporated eloquent will allow for measurements that trick be taken to work out the ideal gas equation. This lab will require knowledge of basic equations used in chemistry. Using these equations, much(prenominal) as density and number of bulwarkes(n), we can substitute different set into the ideal gas law to manipulate it. II. Materials 250-mL Erlenmeyer flask Needle or pin Unknown liquid sampleBarometer 1000-mL beaker Hot plate service program clamp Aluminum freezer foil Hot mitt fit gauze with ceramic center 1000-mL receive cylinder III. Procedure 1. Aprons and gawk on. Clean a 1000-mL beaker for use as a heating bath. flock the beaker on a hot plate and begin heating. 2. Clean and all ironic the Erlenmeyer flask. 3. Cut a square of aluminum foil to perform as the scree n door of the flask. Trim the edges so that it neatly covers the edge of the flask. 4. reflect the empty flask with cover and record to as numerous sigfigs as possible. 5.Obtain your unknown liquid and record the ID . Add 3-4 mL of the liquid to the flask. Re-cover the flask, making sure the edges are tightly crimped. 6. Punch a small hole in the foil cover with a needle or pin. 7. Heat the weewee in the beaker to boiling. Adjust the heat so that the water will remain boiling but will not splash. 8. inhume the flask containing the unknown liquid in the boiling water so that most of the flask is covered. Clamp the neck of the flask. 9. Watch the liquid carefully. The liquid will begin to evaporate, and its volume will decrease. 10.When it appears that the flask is on the whole filled with vapor, continue heating for 1-2 minutes. Remove the flask from the bath using the clamp. 11. garment the flask on the wire gauze on the lab table, shift the clamp, and allow the flask to coo l to room temperature. Measure and record the fill temperature of the boiling water in the beaker, as well as the barometrical pressure in the lab. 12. When the flask has cooled completely, carefully dry the outside of the flask to remove any water. Weigh the flask, foil cover, and vapor with as many sigfigs as possible. 3. Perform a bet on trial, if the final mass of the flask and vapor is not within 0. 05g of the basic trial, perform a 3rd. 14. When devil acceptable trials have been performed, remove the foil cover and clean the flask. 15. fulfill the flask to the very rim with water and pour it into a 1000-mL graduated cylinder to determine the exact volume of the flask. Record. IV. Data and Observations TRIAL 1 TRIAL 2 BAROMETRIC PRESSURE (mm Hg) 763. mm Hg 763. 5 mm Hg bus OF FLASK AND FOIL COVER (g) 106. 095g 106. 095g TEMPERATURE OF wet IN BEAKER (C) and 99. 1C / 372. 1 K 97. 9C / 370. 9 K (K) MASS OF FLASK/COVER AND CONDENSED LIQUID 106. 406g 106. 87g (g) the great unwashed of Erlenmeyer Flask (determined by filling completely with water) 289mL Unknown liquid ID B (ethyl alcohol) V. Analysis of Data PV = nRT visitation 1) 763. 5 (. 289 L) = n (62. 4) (372. 1) 220. 6515 = 23219. 04 n 220. 6515/23219. 04 = n 0. 0095 mol = nMass of vapor in the flask = (mass of flask/cover and condensed liquid) (mass of empty flask/cover) Mass of vapor in the flask = 106. 406g 106. 095g = 0. 311g 0. 311g/0. 0095 mol = 32. 73 g/mol = molar mass Trial 2) 763. 5 (. 289 L) = n (62. 4) (370. 1) 220. 6515 = 23094. 24 n 220. 6515/23094. 24 = n 0. 0096 mol = n Mass of vapor in the flask = (mass of flask/cover and condensed liquid) (mass of empty flask/cover) Mass of vapor in the flask = 106. 487g 106. 095g = 0. 392g 0. 392g/0. 0096 mol = 41. 02 g/mol = molar mass AVERAGE MOLAR MASS (32. 3 + 41. 02) / 2 = 36. 875 g/mol Theoretical molar mass of ethyl alcohol 46. 07 g/mol VI. Conclusion (36. 875 46. 07) / 46. 07 (x 100) = 19. 9% = pct error The first trial was very unsuccessful while the second trial was much closer to the theoretical value. The possibilities of error within the first trial include not letting the flask cool completely to room temperature forwards weighing and also forgetting to utilize acetone to dry the flask before the addition of the liquid. The latter was the major difference in performance of the two trials.This experiment showed that the interference of water vapor can completely wreck the chance for an accurate measurement of volume of a different gas. It is imperative to make sure that the flask is as dry as possible or the results will show a very wrong answer. It is hard to realize the prominence of water vapor in the air until an experiment like this one shows that it takes up a comparatively huge space in a given volume of air. A suggestion to improve this lab could be to place more emphasis on drying the flask with a paper towel and acetone before use.