Experiment 4: Purification of Liquids by Distillation

Transcription

1 Experiment 4: Purification of Liquids by Distillation A. Distillation Procedure: In this experiment, you will perform a fractional distillation on a solution comprised of a mixture of n-butyl acetate and ethyl acetate. This experiment may be done in pairs, if permitted by your instructor. If working in pairs, each student must record the data in his or her laboratory notebook and each student will submit a separate lab report. butyl acetate ethyl acetate Pertinent information regarding the chemicals you are using: Reagents MW (g/mol) MP (ºC) BP (ºC) Density (g/ml) n-butyl acetate ethyl acetate Procedure: 1. Check that all glass equipment is clean and dry before beginning. Label three clean dry sample vials as Fractions 1, 2 and Take the 100 ml round bottom flask at your station to the hood, along with the cork ring, to use as a stand for your flask. Using the provided graduated cylinder, obtain 35-mL of the pre-mixed solution of butyl acetate and ethyl acetate and add this to your round bottom flask, as well as 2-3 boiling stones. Record the actual volume you used. Read that meniscus! bserve what the mixture looks like. 3. Assemble a fractional distillation apparatus (shown on next page, without heating mantle). Securely clamp the round-bottom flask in place at its neck, so the clamp is under the slightly protruding lip of the neck. The flask should be 4-5 inches above the countertop. Align the iron ring underneath it, as it will hold the heating mantle you will use to heat the flask. 4. Your heating mantle has a separate cord be sure to securely plug and twist the cord on, then slide the heating mantle under the round bottom flask and adjust the iron ring so the flask is snuggly nestled inside the mantle. Plug the heating mantle into

2 the Variac (which should be set to off and a voltage of 0). D NT PLUG THE HEATING MANTLE DIRECTLY INT THE UTLETS N THE BENCH! Check that the Variac is plugged into the wall socket. A two-piece unit, consisting of a thermometer adapterr and a distilling adapter may be used Keck Clip H 2 out Clamp to lattice H 2 in Keck Clip 5. Add the Raschig ring column packing to your distilling column enough to fill the column without filling the upper joint. Slide this into the neck of the round-bottom flask and attach a second clamp at the top of the column to secure it vertically. Add the Y shaped distillation head to the top of the column, as well as the thermometer in the thermometer adapter. Be sure to place the thermometer so the top of the mercury bulb is just slightly below the bottom of the sidearm of the distillation head. 6. Attach water tubing to the inlet and outlet of the water-cooled condenser you are using. Wetting the end of the rubber tubing will make it easier for you to slide it on over the glass fingers of the inlet and outlet. Connect the lower inlet to the water faucet (labeled green CW ) in the trough in front of you and place the drainage tube from the outlet also in the trough. Use a Keck clip to secure the water-cooled condenser to the distillation head. Add the vacuum adapter to the other end and secure the vacuum adapter to the water-cooled condenser using a second Keck clip. Add a clamp to secure the water-cooled condenser to the bench lattice. A Keck clip may also be used to secure the distillation head on the distilling column, if desired. 7. Align a 10 ml graduated cylinder under the drip tube of the vacuum adapter. Clamp in place. HAVE YUR INSTRUCTR CHECK YUR APPARATUS BEFRE PRCEEDING FURTHER. 2

3 8. Turn on the Variac and start heating with the VARIAC set to 90. As the solution heats up, you should begin to see boiling (observation!) occur in the round bottom flask. Watch for the reflux line (observation!) and make note of it in your notebook when you see it. Allow the apparatus to continue to heat up until enough vapors condense and liquid begins to drip out of the apparatus into the 10 ml graduated cylinder. You should begin collecting temperature data when the first drop is collected for this first fraction. nce that 10 ml sample is collected, record the temperature, and switch to a new 10 ml graduated cylinder. D NT VERFILL THE GRADUATED CYLINDER or you will not be able to accurately measure the volume! bserve what the first fraction looks like. Pour this first 10 ml sample into the vial for Fraction 1. Use the blow dryer to blow out any remnants of solution from the first 10 ml grad cylinder (do not clean by washing with water). 9. Now that you are collecting the second fraction, increase the setting on the VARIAC to 125 for the remainder of the distillation. Repeat the process of obtaining a 10 ml sample again. The second fraction contains both compounds and you may see the difference as the new compound drips into the old compound (observation!). The ending temperature for the first fraction is the beginning temperature for the second fraction. After 10 ml has been collected, swap again to the clean dry 10 ml graduated cylinder you used for the first fraction and record the temperature of the last drop in Fraction 2. Pour the 10 ml sample into the vial for Fraction 2. bserve what the second fraction looks like. Use the blow dryer to blow out any remnants of solution from the second 10 ml grad cylinder (do not clean by washing with water). 10. btain the third fraction. The ending temperature for the second fraction is the beginning temperature for the third fraction. Watch the temperature as you may see it drop as you begin to run low on liquid for your distillation. Make note in your observations if the temperature begins to drop. After 10 ml has been collected, record the temperature for the final drop, and place the grad cylinder from Fraction 2 under the opening of the vacuum adapter to catch random drops until the apparatus cools. Turn off the Variac and loosen the iron ring so the heating mantle can be removed from under the round bottom flask. Allow the apparatus to cool. 11. nce entirely cooled, record the volume of the non-distilled liquid (called the pot residue) that remains in the round bottom flask. Pour this pot residue into the graduated cylinder currently collecting random extra drops from the vacuum adapter, to see what volume of liquid was not distilled into Fractions 1, 2 or Your laboratory instructor will provide you with three GC sample vials to be used with the GC autosampler. These cannot be labeled so you will need to keep track of which one is which as you fill them. Transfer each fraction to a clean GC vial using a clean, dry pipette, filling the sample vial (at least 3/4 of total volume). Do not cross contaminate by using the same pipette for each sample. Place in designated automatic 3

4 sampler tray on the front bench and sign in on the sign-in sheet for whichever set of slot numbers your samples are in. In your distillation data table, record what slot numbers you placed your vials in. Without this information, you will not be able to identify what GC traces correspond to your experiment. 13. nce your apparatus has cooled, carefully remove each piece of glassware and wash thoroughly with soap and water. The glassware may not be return to its blue box if they still contain organic solvent. Distillation Data Table: Initial Volume: Fraction Number Volume Collected BP range GC Vial Slot pot residue volume: Waste Disposal and Clean Up: a. Pot Residue place in distillation solvent bottle in hood, after determining volume remaining in your flask. b. Column packing place in used column packing beaker in hood. c. Fractions Tightly cap each of the sample vials, place them in a beaker to prevent them from tipping over, and store them in your personal locker until GC analysis is completed. d. Clean and put all glassware and equipment in proper locker. Wash and dry your personal work area. B. Gas Chromatography No Procedure. The details for analysis of the data will be discussed in lab lecture. The laboratory report of each student must contain a copy of the GC analysis traces even though the distillation was done in pairs. Waste Disposal and Clean-Up: 1. After receiving GC traces for results analysis, place the rest of each sample in "distillation waste container in hood. 2. Wash sample vials and place them in your personal locker. C. Data Analysis (as required by Instructor) Do the following calculations in your laboratory notebook: 4

5 1. Make a separate table for GC results, summarizing the relative peak areas and retention times for each peak in the three GC traces. Note that there should be two peaks per GC trace - one corresponding to ethyl acetate and one corresponding to n- butyl acetate. You should also include retention times for the two standard GC traces for comparison Gas Chromatography Data Table: GC Trace #1 Retention Time Relative Peak Area Percent Composition GC Trace #2 Retention Time Relative Peak Area Percent Composition GC Trace #3 Retention Time Relative Peak Area Percent Composition 2. If needed, calculate the percent composition for each ester in each fraction that has more than two peaks. First, identify which two peaks are butyl acetate and ethyl acetate, using the known retention times. Second, calculate the total area of the two peaks (add the areas of the two peaks together). Third, divide each individual area by the total area and multiply by 100 to obtain your answer in a percentage. If all of your GC s only have two peaks, no calculations will be required. 5