Exp1 Ebulliometry PDF

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Experiment 1: Ebulliometry

Tasneem Abdalla S2954210

Introduction: This experiment determines the boiling point constant of toluene and use it to measure the molar mass of benzoic acid in toluene solution. Colligative properties depend on the number of solute molecules in the solvent molecules in the solution, which include, billing point, freezing point, osmotic pressure and equilibrium vapour pressure. In this experiment, we used boiling point to calculate the toluene solution, using the 2v range for the voltmeter, toluene was set to 110.6(degrees) boiling point. In this report, there will be several calculations showing the molar mass of the samples used, the graphs for the calculations and explanations to how we achieved these results.

Method 1. Weigh 3 samples each of ~0.2 g for naphthalene, benzoic acid and biphenyl into plastic weighing boats using a 2 place balance (i.e. 3 × 3 = 9 tablets in total). 2. Form these samples into tablets using the die press. Consult your demonstrator for DIE PRESS instructions. 3. Pipette exactly 10.0 ml of toluene into a clean dry ebulliometer flask. Calculate the mass of toluene added. Toluene: (20°C) = 0.8669 g ml-1 Consult your demonstrator for EBULLIOMETER instructions. 4. Carefully fit the flask into the heating apparatus into the ebulliometer heater. Add the cold finger reflux to the reflux arm of the flask. Carefully add the temperature probe to the flask. 5. With water flowing through the reflux cold finger, turn on the heater to its maximum setting. Monitor the temperature inside the flask when boiling commences. When a vigorous boiling action produces a steady temperature, adjust the offset to that of the boiling point of toluene ; i.e. using the Control Box, adjust the reading to 1.106 V (a 10 mV increment of voltage would thus correspond to a temperature difference of 1 K). 6. Weigh a tablet of naphthalene on the analytical balance (4 places) and add it to the ebulliometer flask via the reflux arm. The tablet will dissolve, and a new temperature of equilibrium boiling will be established. Record the new boiling temperature and the mass of naphthalene in your results table. 7. Repeat step (5) with another 2 tablet additions. Record the naphthalene tablet mass and the new boiling point in each case. Then turn off the heater and carefully raise the ebulliometer flask to cool. 8. Empty the cooled flask contents into an organic waste bottle provided in the fume cupboards. Thoroughly clean the flask by washing more than three times with approximately 5 ml portions of dichloromethane, followed by air-drying. 9. Repeat steps (1) to (5) using firstly benzoic acid tablets, then biphenyl tablets, in place of naphthalene. Again, record the boiling point of the solvent before and after each of three successive additions of pre-weighed tablets. 10. When all readings have been taken, cool the flask and clean and dry as before in step (8).

Results: Weight of each 3 samples:Napthalene 0.215g 0.201g 0.206g

Benzoic acid 0.19g 0.19g 0.20g

Biphenyl 0.20g 0.20g 0.20g

Table results for naphthalene experiment: added msolute (g) cumulative msolute (g)

nsolute (mol)

bsolute (mol kg1)

boil (°C)

T (K)

Nap1: 0.1804g Nap2: 0.1992 Nap3: 0.2032g Benz1:0.1969 Benz2: 0.1934 Benz3: 0.1979 Biph1: 0.1966 Biph2: 0.2069 Biph3: 0.1972

0.00143 0.00155 0.00158 0.00161 0.00158 0.00162 0.00127 0.00134 0.00128

0.00799 0.07842 0.00783 0.00824 0.00823 0.00825 0.00650 0.00652 0.00653

1.1118 1.1178 1.1237 1.1121 1.1168 1.1207 1.1131 1.1206 1.263

274.1118 274.1178 274.1237 274.1121 274.1168 274.1207 274.1131 274.1206 274.263

0.17897 0.19765 0.20162 0.19529 0.19182 0.19628 0.19533 0.20556 0.19592

Molar Mass of naphthalene: 128.1705g/mol Molar Mass of Benzoic acid: 122.12g/mol Molar Mass of Biphenyl: 154.21g/mol

Nsolute: mass/Molar mass Added msolte/molar mass of 3 smaples, example: nsolute for naphthalene 1: 0.1804/128.1705= 0.00143(mol) Bsolute: nsolute/cumulative msolute Napthalene Kb: 1 Benzoic Acid Kb: 0.9971 Biphenyl kb: 0.7874 ** Kb was calculated from the samples graphs’ slope**

Discussion: The measured molar mass of benzoic acid differs from the formula mass (C 6H5COOH) because of certain aspects that would either make the concentration (measurement) higher or lower. For example, the interference of hydrogen bonds and their attraction requires greater kinetic energy and therefore we would have a higher measurement of boiling point thus, greater concentration to the actual formula mass of benzoic acid. Another factor that has an impact on the measurement of sample concentrations can be standard enthalpy, if we have a higher concentration there will be an increase of enthalpy and might affect the measurement of mass of Benzoic acid. Conclusion: This experiment was set to determine molar mass by elevation of boiling point, using three samples: Naphthalene, Benzoic Acid, Biphenyl. Using the method Die press, and after using Ebulliometer to determine that the mass of toluene added at 20(degrees) had a mass of 0.8669 gml-1, So the result was, toluene for naphthalene had a boiling point of 1.106(degrees), Toluene for Benzoic acid is 1.1063 (degress) and boiling point for Biphenyl is also 1.1063(degrees). Due to some errors made in this experiment the results showed that the molecular weight of Benzoic acid is 122.12g/mol and it is accurate for most of the samples made, therefore, to avoid errors next time, more samples ust be prepared and that we have precise calculations and measurement do compare experiment with natural calculations and why might the measurement be higher or lower....