Lab Activity 10: Separations: and Rotary Evaporator

Part A. Separation, Isolation, And Purification By Distillation. 1. Look up the lab techniques in Table 1, identify the equipment used (see Figure 1), and the property used to achieve separation.

Table 1. Lab Techniques Information. Lab Technique Identify the equipment used Property used to achieve separation Filtration: name the two types used in Chem 1A and 1B Distillation: simple and fractional Recrystallization Sublimation (skip this one) Extraction Drying agent Chromatography

2. a. What property tells you whether one substance is soluble in another? b. How is structure and shape related to this property? c. What intermolecular forces are related to the polarity of a compound?

3. a. A _____-_____ mixture is separated in a distillation. (Hint: see state of matter.) b. The _____ property of a substance is used to separate a mixture in a distillation. What chemical force determines this property?

Distillation is one way to separate, isolate, and purify a mixture. You have a solution of two liquids, Liquid A and Liquid B. You want Liquid A. Liquid A has a lower than Liquid B. Problem: How do you separate this mixture and collect Liquid A? Answer: distillation. (You did a macroscale distillation in CHM 1A lab when you distilled an ethanol-water mixture.) 4. a. You’ve been using your microscale kit. (i) What parts would you use to set up a simple distillation and a ? (ii) Draw a picture of each distillation set-up. Name and describe the function of each part. (iii) Show the path and state of matter of Liquid A as the distillation occurs. b. At the end of a distillation, the low boiling point liquid is in the _____ flask and the high boiling point liquid is in the _____ flask. c. The difference in boiling point between the two liquids you want to separate determines whether you should you do a fractional distillation or simple distillation. What should the difference in boiling point be to do a fractional distillation instead of a simple distillation? d. How is a distillation different than a ?

5. You are working at a distillery to make whiskey. Flavoring compounds determine how the whiskey tastes. Table 2. Flavoring Compounds in Whiskey (taken from H. Wan, et al., J. Chem. Educ., 2014, 91, 123.) Compound Ethyl acetate 2-butanone 2-propanol 2-pentanone Ethyl butyrate 3-methyl-1- 1-pentanol butanol Boiling point, 75-77 79-81 81-83 101-105 119-121 129-131 136-138 oC Flavor Fruity, brandy ethereal butter apple Banana, whiskey Sweet, pineapple vanilla

One batch of whiskey tastes different than another batch so you decide to analyze the whiskey by extracting the water and ethanol from the flavoring compounds. a. You have a mixture of 2-propanol and 2-pentanone. Would you use a simple distillation or fractional distillation to separate this mixture? Give reasons. b. Graph 1 shows 2-propanol and 2-pentanone distillation data with temperature in oC on the y-axis and volume of distillate in ml on the x-axis.

110

105

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95

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70 0 2 4 6 8 10 12

Graph 1. Distillation data for 2-propanol and 2-pentanone.

(i) Which substance is being distilled in the first 4 ml of distillate? What property of this substance is shown in this graph? (ii) How does this graph show 2-propanol is separated from 2-pentanone by distillation? c. You have a mixture of 1-pentanol and 2-butanone. Would you use a simple distillation or fractional distillation to separate this mixture? Give reasons.

6. When would you use a distillation? When would you use a recrystallization?

We will do a distillation in Lab 6.

References on distillation: https://www.youtube.com/watch?v=Vjt8Oq5G8Vo http://www.orgchemboulder.com/Technique/Procedures/Distillation/Distillation.shtml http://www.wiredchemist.com/chemistry/instructional/laboratory-tutorials/distillation

Part B. Separation By Rotary Evaporator. A rotary evaporator (rotovap) is a device that separates a from a sample by evaporation under reduced pressure. Our rotovap is shown in Fig. 1. The components are: 1 = Power control. On/off switch on lower left side. One knob controls the heater to the water bath; the other knob controls the motor that rotates the evaporating flask. 2 = evaporating flask that holds the sample mixture. This flask is attached to a motor that rotates the flask in the heating bath. 3 = . This consists of two parts: A tube (“cold finger”) fits into a larger tube that is attached to the collecting flask. 4 = collecting flask. 5 = vacuum pump. 6 = heating bath. 7 = knob that moves heating bath left or right. 8 = lever that tilts condenser, evaporating flask, and collecting flask into heating bath.

Read “Rotary evaporator” in Wikipedia (https://en.wikipedia.org/wiki/Rotary_evaporator) A rotovap can be used to separate a solid-liquid solution (the solid is soluble in a liquid solvent) or two miscible liquids (the liquid is soluble in a liquid solvent. (remove) a liquid low boiling point solvent from a substance solid

Fig. 1. Rotary evaporator components.

1. a. What is the boiling point of ethanol at P = 1.0 atm? b. Is the boiling point of ethanol at P = 0.5 atm greater than, less than, or equal to your answer in (1a)? c. Explain why the boiling point of a liquid changes when the pressure decreases.

2. Your sample goes in the evaporating flask (2 in Fig. 1). What is the reason for rotating this flask in a heated water bath?

3. See the condenser (3 in Fig. 1). Remove the rubber cap from the top. Next, carefully remove the inner tube. How will you cool the vapor to make it condense to a liquid?

4. How is a rotovap similar to a distillation? The difference between a distillation and rotary evaporation is ____. You cannot use a rotovap to separate water from ethanol because _____. Remove a high bp solvent vs. low bp solvent.

5. Use and operation of rotovap. Add ____ ml of _____ and _____ g or ml of ____ to evaporating flask. OR just add one solvent, e.g., EtOH, to flask. Turn on rotovap. Turn dial so evaporating flask starts to rotate. How fast should it spin? Turn on heating bath. Add enough water to bath so evaporating flask is partially immersed when tilted (See 8 in Fig. 1). Let run for 5 min. Is any solvent evaporating? Is any liquid condensing to collecting flask? Turn on pump. After 30 seconds, see pressure gauge on pump. Record pressure in atm. Is any solvent evaporating? Is any liquid condensing to collecting flask?