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Expt. 3 Part 3x: Determine Boiling Point of Reference Liquid and of an Unknown Liquid Expt. 5.1A: Simple Distillation of Cyclohexane:Toluene Mixture Expt. 5.2A: Fractional Distillation of a Cyclohexane:Toluene Mixture

Rebecca Gotthelf CHE210L Lab Section A 9/28/17; 10/5/17

I.

Abstract The objectives of Experiment 5.1 and Experiment 5.2 were to perform a simple and fractional distillation of a cyclohexane; toluene mixture. The goal of the experiment was to increase the temperature of the mixture so that two drops of distilled mixture are collected per minute. For simple distillation, a long-necked flask is used, whereas for fractional distillation utilizes a short-necked flask. The results of both of these different kinds of distillations should be visible in the graph, where simple distillation is a gradual curve, whereas for fractional distillation, there’s a jump in temperature in which the mixture vaporizes at. For Experiment 3.x, the boiling point of an unknown compound needed to be determined using an unknown and a reference compound. The boiling point of the reference compound, acetone, was 56.3°C, the boiling point of the unknown substance 137 was approximately 76.1°C, which was consistent with the boiling point of ethyl acetate.

II. Introduction 1. Explain what is meant by the term “the boiling point of a liquid.” The boiling point of a liquid is technically when the vapor pressure of the liquid is equal to the pressure of the gas that is above it. The higher the pressure, the higher the boiling point, as applies to lower pressure and boiling point. 2. Explain the three types (ignore ion-ion) of intermolecular attractive forces. The three types of intermolecular attractive forces are, London dispersion forces, dipoledipole, and hydrogen bonds. London dispersion forces are temporary attractive forces when the position of the electrons in two adjacent molecules form an extremely weak, temporary dipole attraction. Dipole-dipole bonds occur when two partially, oppositely charged molecules are adjacent to each other and the partially positive molecule bonds with the partially negative molecule. Lastly, the hydrogen bond is an attraction between the hydrogen atom of a molecule bonds to a highly electronegative atom, which can be either, fluorine, oxygen, or nitrogen.

3. There are three main factors you need to think about when confronted with a question about boiling points. 1) what intermolecular forces will be present in the molecules? 2) how do the molecular weights compare? 3) how do the symmetries compare? Using the abo abov ve criteria determine in each of the following pairs of compounds which has the higher boiling point and why it has the higher boiling point. a. t-butyl alcohol (2-methyl-2-propanol) or n-butyl alcohol (1-butanol) [both are C4H10O alcohols] The molecule with the higher melting point would be the t-butyl alcohol due to its structure. This molecule has a branched structure, rather than a linear structure which means that it has a higher boiling point. Other than

that, the molecular formulas of the two molecules are the same, indicating that there are the same intermolecular forces and the same molecular weight. b. 1-butanol (CH3CH2CH2CH2OH) [an alcohol] or diethyl ether (CH3CH2OCH2CH3) [an ether] 1-butanol would have a higher boiling point than the diethyl ether. This is due to the alcohol group (OH) at the end of the 1-butanol which enables it to make hydrogen bonds, whereas the diethyl ether cannot. This leads to stronger intermolecular forces, and an overall higher boiling point. 4. In distillation and especially fractional distillation, liquid can be seen running from the bottom of the distillation column back into the distilling flask. What effect does this returning condensate have on the fractional distillation? The liquid going back into the distilling flask interacts with the vapor coming out of the flask, and can increase the concentration and volatility of the fraction.

5. Experimental Section: Procedure: This procedure was taken from page 92-95 and57-58 of “Macroscale and Microscale Organic Experiments 6th Edition”. There were no modifications made to the procedure.

6. Results and Discussion Data: Experiment 5.1 and 5.2

Fractional and Simple Distillation of Cyclohexane; Toluene mixture

Temperature(celcius)

120 100 80 60 40 20 0

Volume of Distillate

Experiment 3.x

BP of acetone: 56.3°C BP of unknown 137: 76.1°C = ethyl acetate

Analysis: For Experiments 5.1 and 5.2, the two separate curves in the graphed data are supposed to have distinctly different properties. Simple distillation is supposed to have a gradual “S” looking curve, where the points all mold together, whereas with the fractional distillation, there is supposed to be a relatively sharp incline when the boiling point of cyclohexane ends and toluene begins. In this data, the blue line is simple and orange is fractional. Simple is a bit more gradual, however the fractional distillation is not nearly as sharp of a change as would have been expected. Some possible sources of error that could have resulted in the data being skewed like this could be, having more than 2 drops come out at once, changing or not changing the temperature fast enough, or recording too few or many data points. All of these sources of error could have led to the graph looking like this. As the cyclohexane; toluene mixture is distilled, it becomes more pure, the impurities evaporate out, and the pure samples of each compound are collected as the condense. For Experiment 3.x, the thermometer was held above the liquid, due to the fact that the gas above the liquid is the true boiling point, because that is where the liquid is becoming a vapor. Initially acetone was used to see how the thermometer was reading, due to the fact that the boiling point of acetone was previously known. Then, Unknown 137 was used and the boiling point of that liquid was compared to a list of known liquid boiling points, and it was deduced that unknown 137 was ethyl acetate.

7. Works Cited Williamson, Kenneth L.; Minard, Robert D.; Masters, Katherine M. Macroscale and Microscale Organic Experiments, 6th ed., chapters 3 and 5; Houghton Mifflin Co.: New York, 2007....