Experiment order to determine the unknown triplet point
Experiment 2: Intermolecular Forces Performed: 9/12/2011 Submitted: 9/20/2011 Chemistry 1046L PART I: Purpose: The purpose of partI in this experiment is to identify a variety of unknown substances’ properties using observations of the temperature changes that occur during evaporation. We know that substances with weaker intermolecular forces, such as London dispersion, will have a faster vaporization rate and thus a higher temperature difference compared to those with stronger molecular bonds such as hydrogen and dipole-dipole forces.By measuring the average kinetic energy (or the temperature) of the liquid left behind after some evaporation takes place, we can determine its type of intermolecular forces and ultimately identify the unknown liquid when compared to other substances. Another purpose of part I of this experiment is to reiterate the use of web- based data and tables to organize our numerical results as well as deltaHvapand delta T calculations of substances.
Also to teach the proper use and technique of laboratory materials such as the clamp apparatus, beaker, pipet and thermometer.Data: Observations: Unknown substance B had a mild scent of nail polish remover; Unknown E smelled similar to spray paint before and after probe soak and unknown D exhibited scent similar to rubbing alcohol. Unknown A, C had no smell. All five unknown were clear, colorless liquids. A: Table of Temhttp://answers. yahoo.
com/question/index? qid=20100718190731AAQZ2dKre values (Tfinal-Tinitial) for the five unknown liquids (A-E) UnknownT initialT finalTf-Ti A21. 5 C8. 8 C8. 8-21. = -12. 7 B18. 0 C10.
9 C10. 9-18. 0 = -7. 1 C23. 0 C18. 0 C18.
0-23. 0 = -5. 0 D23. 5 C16.
0 C16. 0-23. 5 = -7. 5 E23.
0 C10. 0 C10. 0-23. 0 = -13.
0 B: rankings of the unknown liquids from strongest (1) to weakest (5). Based on the T values found, the highest temperature decrease will have the weakest intermolecular forces and vice versa. 1. C 2. B 3. D 4.
A 5. E C: identification of the unknown liquids” A: Acetone B: 2-Propanol C: Water D: Methane E: Hexane PART II: Purpose:The purpose of this portion of the experiment is to observe the “phenomenon of the triplet point”, at which a substance exhibits properties of all three phase categories. Also, to familiarize students with Boyle’s law to determine the pressure neededin order to determine the unknown triplet point as well as calculating percent error to accurately publish our experimental data. Data: Observations: Dry ice was white, cylindrical shaped solid that smoked and sublimed when placed onto paper towel. The solids were crushed into a fine grain and a few small chunks.
While in the pipet, the dry ice crystallized on outside bottom and inside some layer of “fog” and smoke was created. During submersion into the cup of water, the dry ice observed began to liquefy (the triple point) and after the first slight release of the pliers on the pipet, there was an explosion. Calculations: P1 V1 = P2 V2 Pressure of the room taken off the barometer: 10125 kPa 1015 kPa X 1 atm = 10. 02 atm 101.
325 kPa (10. 02 atm)(5 mL) X (P2 )(3 mL) P = 16. 7 atm % Error = 16. 7 – 5. 1X 100= 233% 5.
1 Conclusion:Based on the observations, it is concluded that unknown C is water because this substance has the least decrease in temperature which correlates to high intermolecular forces. Out of the five unknowns, water has the strongest intermolecular forces having hydrogen bonding. The substance with the weakest intermolecular forces and lowest empalthy of vaporization is unknown E based off the high rate and magnitude of temperature difference observed. From this, it is concluded that unknown E is Hexane which correspondingly has dispersion forces between its molecules which is the weakest of the types.Unknown B is 2-propanol with the second strongest intermolecular forces because it is right below water with the second highest amount of heat needed to evaporate and because it has the capacity for hydrogen bonding. Unknown d is methane, made up predominantly of dipole-dipole interactions and unknown A is concluded to be Acetone, also dipole-dipole interactions but a lower boiling point and smaller chain. For Part II, the white, cylindrical solid carbon dioxide began to liquefy in a pipet while submerged in water to display its phase change through its triple point determined to be at 10.
2 atm based off observations that the dye traveled from 5cm down to the 2cm marker on the pipet. This experimental value has ~ 200% percent error when compared to CO2’s triple point actual value found to be at 5. 11 atm. This percent error could have been caused by human error- some misreading of the thermometer or barometer in the classroom. Another error incurred was noted during identification of unknown B, due to a possible additional amount of water present in the solution caused by re-use of original probe used during evaluation of unknown A. Questions: 1.
The change in temperatures we observe as the various solvents evaporate is related to their deltaHvap because the rate of evaporation is indirectly proportional to their deltaHvap. The weaker the intermolecular forces, the lower amount of heat need to produce a phase change from a liquid to a gas. The solvents needing the least amount of energy and having the weakest intermolecular forces will have the highest temperature difference. It will have evaporated the quickest compared to the solvents with stronger intermolecular forced and a higher deltaHvap because those need much more heat and energy to evaporate.
Those stronger solvents will have the highest deltaHvap and will have exhibited the least temperature difference between Ti and Tf. 2. In determining the tripe point of CO2 we did not find the actual volume because the diameter of the pipet was constant during this experiment. This approximation does not ruin our results because if both sides of the equation are equal, it will cancel each other out so only the h, or height, portion of the volume equation was measured using the distance traveled by the dye.
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