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12 Dec 2019

Post Lab Questions Fermentation:

1. What physical property enables one to use distillation for the separation of ethyl alcohol enriched from the water mixture?

2 What is an Azeotrope? Explain how can azeotropes be used to purify mixtures?

3. Azeotropes are also defined as liquid mixtures having a vapor pressure at constant temperature, as a function of composition. Explain with your own words why vapor pressure depends on the composition of the mixture.

4 If the distillation temperature is different from the theoretical distillation temperature, why do you think this is so?

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Hubert KochLv2

13 Dec 2019

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1.[ Plot temperature (oC) vs. volume of distillate (ml) collected for the mixture with and without the fractionating column. Use the graph to determine the boiling ranges of the two compounds in the mixture and identify the compounds. Plot both sets of data on the same graph]- I know how to do that part and by the way the unknown compounds are acetone and 1-propanol. --Also plot on this graph an ideal distillation curve. Why are the real distillation curves different from the ideal? 2. Use a vapor/liquid diagram to explain the differences in the simple and fractional distillation plots. Describe what is happening in the fractionation column and explain why this results in a better separation with purer components isolated. 3. Why is it important to maintain a distilling rate of ~0.5 drop/s? Why not faster or slower? 4. What is an azeotrope? Sketch a distillation curve (as in Question 1) for a simple distillation of a mixture of toluene (70 ml) and water (30 ml). Explain the behavior of the curve.

ivoryant353

Please give me Post lab questions 2 and 3 at the bottom.

Experiment 7 - Molar Mass of a Volatile Liquid

Introduction. Given the mass of vapor at conditions of known pressure, volume, and temperature, one can determine the molar mass of the vapor. The Ideal Gas Law mathematically relates the quantities of pressure (P in atm), volume (V in liters), and temperature (T in Kelvin) and the quantity of gas (n in moles). Using the expression PV=nRT where R equals the Ideal Gas Constant 0.0821 L*atm/K*mol, one can determine the quantity of gas under given conditions of pressure, volume and temperature. The number of moles of gas is found by

n =

Because the molar mass (MM) is defined as the mass of one mole of substance in units of g/mol, the molar mass of the vapor can be determined by

MM= mass of vapor in grams/moles of vapor

In this experiment, an unknown volatile liquid is heated in a boiling water bath and is vaporized. The vapor forces air from the flask until the pressure within the flask equals the barometric pressure of the lab. As with all gases, the vapor occupies the entire volume of its container. The temperature of the vapor equals the temperature of the boiling water bath. After 8-10 minutes, the vapor is cooled. The mass of the condensed liquid is determined and the molar mass is calculated as described above.

Notes:

Check out unknown from stockroom

Record unknown number

Before weighing your condensed vapor, thoroughly dry the outside of the flask and make sure that no water is trapped under the foil cover

Do not rinse your flask with water between trials

Dispose of waste in appropriate container

Procedure. You will record your data and calculations in your lab notebook.

Obtain an unknown liquid and a 3 inch aluminum foil square. You will need two 600 or 800 mL beakers, and 3 or 4 boiling chips.

Add 3 or 4 boiling chips to the water in an 800 mL beaker and heat the water to the boiling point. Continue heating for 8 to 10 minutes after the water comes to a rolling boil. The temperature of the boiling water is 100.0^oC. This will be the temperature of the vapor. Convert the temperature to Kelvin and record in your lab notebook.

800 mL Beaker

250 mL Flask

11.

Chemical Molar Mass

1-chlorobutane 92.6 g/mol

t-butyl chloride 92.5 g/mol

trichloroethylene 131 g/mol

2-propanol 60.1 g/mol

Ethyl acetate 88.1 g/mol

n-hexane 86.2 g/mol

cyclohexane 84.2 g/mol

2-butanone 72.1 g/mol

Post Lab Questions: Answer the following questions using complete sentences. Include them after your conclusion.

1. If a lab group did not keep the flask submerged in boiling water for a full ten minutes, and some unknown never vaporized, how would that affect the calculated molar mass? In other words, would it make the calculated value too high or too low? Explain why.

2. While performing this experiment, ten lab groups have ten different unknown volatile liquids with a range of molar masses. If all lab groups have exactly the same size of flask (255 mL), and all groups took their unknown vapor to the same temperature (100.0^oC) and pressure (760.0 mmHg), how would the number of molecules within the different flasks compare? Would it vary with molar mass? How? Explain.

3. A student has determined that an unknown liquid is either 1-chlorobutane or t-butyl chloride. What other physical property(s) could be used to determine the identity of the unknown?

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