Lab 7_ Boiling Point Determination

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Temple University *

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2201

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Chemistry

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Jan 9, 2024

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Lab 7: Boiling Point Determination Goal: To learn boiling point measurement techniques by identifying the unknown compound using the boiling point and IR spectroscopy. Background: A boiling point is a physical property that can be very useful in identifying an unknown substance. As we previously distinguished with melting point, physical properties usually remain the same for a given substance no matter how much of it is present. Distinguishing the boiling point of an unknown is different than that of a melting point. This can be done using various methods, one of which is the macroscale method of determining the boiling point. An unknown substance is placed in a test tube inside boiling water with a mercury thermometer hanging right above the substance. Once a constant drop of condensation is dripping from the thermometer this will indicate the boiling point of the unknown. Given Table of Context: Standard: Boiling Point ( C ): 1-propanol 97.0 Cyclohexene 82.8 Cyclohexane 80.2 Ethanol 78.4 Ethyl Acetate 77.1 n-hexane 69.0 1-hexane 63.5 acetone 56.0 Equipment: ● Hot Plate

● Beaker ● Test tube ● Thermometer ● IR spectroscopy apparatus Procedure: 1. The apparatus was set up by using the named equipment. 2. About 1cm high of unknown liquid was placed in a test tube which was then lowered into a beaker with water on a hot plate. 3. A thermometer was placed approximately 1cm higher above the unknown liquid 4. Constant drip from the bottom of the thermometer was observed and the temperature was recorded. 5. A sample of the unknown was put in the IR spectroscopy apparatus and the spectrum was obtained. 6. Once a standard was proposed and checked with the instructor, a part of the unknown was added to a part of the identified standard to measure the boiling point 7. Then, the unknown was mixed with another standard and the boiling point was obtained. Results: Unknown # and identification 10 b.p - identified as ethanol Unknown (ethanol) b.p 79.0 C Unknown + equal amount of standard b.p 78.0 C Unknown + ethyl acetate (another std) b.p 76.5 C Conclusion: By running the experiment, I was able to identify my unknown which was 10b.p as ethanol. While it was boiling the constant drip of my product was recorded at 79.0 C, which closely resembles that of ethanol from the table of contexts. Then, to solidify my findings, the unknown was tested in the IR spectroscopy. In the attached wavelength spectrum, I was able to

identify the strong O-H bond ranging between 3300-3600 cm-1, this is a functional group commonly found in ethanol. Once I confirmed that my unknown was ethanol, I repeated the boiling point determination with a standard ethanol and in the third run with another standard which was ethyl acetate. The recorded temperatures for boiling point are provided. Changes: - No significant changes were noted Discussion: Although the experiment was significantly simple there could have been lots of external factors that might have messed with my results. Next time I run this test I will pay extremely close attention to the drip at the end of the thermometer because I was about 1 degree away from identifying my compound as cyclohexane. In this case, IR spectroscopy served to confirm the exact property of the unknown compound. I believe that if this experiment had been done without the use of the IR spectroscopy apparatus, my identification would have been wrong. Questions: Q1.) Using the pressure-temperature alignment chart in Figure 13.2, answer the following questions. A.) What is the normal boiling point (at 760 mm Hg) for a compound that boils at 150C at 10 mm Hg pressure? - 300 C B.) At what temperature would the compound in (a) boil if the pressure were 40 mm Hg? - 185 C C.) A compound was distilled at atmospheric pressure and had a boiling point of 285C. What would be the approximate boiling range for this compound at 15 mm Hg? - 150 C Q3.) Suppose that you had calibrated the thermometer in your melting-point apparatus against a series of melting-point standards. After reading the temperature and converting it using the calibration chart, should you also apply a stem correction? Explain.

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- It would not be necessary to use the stem correction since the thermometer had already been calibrated as they read the correct measurement. Q4.) The density of a liquid was determined by the automatic pipette method. A 100-mL automatic pipette was used. The liquid had a mass of 0.082 g. What was the density in grams per milliliter of the liquid? - 0.00082 grams per liter