Good Morning! :) Please hand in the lecture problem on the desk in front BEFORE lecture begins! You will not be allowed to hand in the lecture problem once the answer has been given.
Distillation & Boiling Point Next Week in Lab: Chapter 5 Experiment • Note: Fill in the Common Shelf Chemical Data Table. Once complete, • photocopy, and hand in with Ch 5 PreLab. Chemicals that appear on • this table are not included on the regular chemical data tables. • When using Aldrich, pick the chemical entry that does NOT have • isotopic labeling, e.g, d, 15N, 13C. These are more expensive and will • have different FWs. Aldrich will also tell you if a chemical is • flammable, toxic or an irritant. • This Week In Lab: • Ch 4: Recrystallization/Melting Point, Procedures 1, 2, and 4 • (Procedures 3 and 5 can be done next week) • Hand in Ch 4 PreLab • Quiz 1
Distillation & Boiling Point • Distillation: • Purification technique • Used to separate components of a liquid mixture or to purify an • impure liquid • Several basic types/variations: • Simple distillation • Fractional distillation • Simple, high vacuum distillation • Steam distillation • Boiling Point: • Physical property of a compound • Used to identify an unknown
The Distillation Experiment: Ch 5 • A two-day lab • Day One: • Based on your desk location, you will be doing one of the four following distillations: • Macroscale simple distillation (Procedure 1) • Either a cyclohexane/toluene mixture OR an ethanol/water mixture (Fig. 5.3) • Macroscale fractional distillation (Procedure 2) • Either a cyclohexane/toluene mixture OR an ethanol/water mixture (Fig. 5.4) You will share your data with some of your bench mates then graph each set of data. You will then assess and compare the effectiveness of simple and fractional distillations.
Simple vs. Fractional Prediction: Fractional distillation is a more effective purification technique than simple distillation. An example Excel graph with two data sets superimposed: bp of pure B A two- component mixture: A & B Simple distillation Temperature (°C) Fractional distillation bp of pure A Drops of Distillate
Simple vs. Fractional • Simple Distillation: • Used to separate mixture into pure components • Works best if components’ boiling points differ by at least 75°C • Fractional Distillation: • To be used when components’ boiling points are closer together • Unlike simple, uses a fractioning column; this column may be packed with material so as to increase the surface area for heat exchange, thus increasing the number of theoretical plates. • The more theoretical plates, the better the purification/separation. Theoretical Plate: one cycle of vaporization and condensation Refer to Fig. 5.1
The Distillation Experiment: Ch 5 Day Two: Procedure 3: A microscale distillation of a 50:50 unknown, two- component mixture. Based on the observed boiling point data, determine the identities of the two components in your unknown mixture. Graph data in Excel. Also, do solubility tests on each of the purified liquids to confirm identities. Possible unknowns: acetone, methanol, hexane, t-butanol, water, toluene, 1-butanol Refer to Fig. 5.5 - Insulate your set-up with glass wool and be sure to use the correct column (distilling column) from your microscale kit!!!
Distillation: Natural Product Isolation Steam distillation of citral from lemon grass oil Citral (oil) comprised of: • Uses of citral: • Defense pheromone for ants • In perfumes for lemon-like scent • Precursor to vitamin A
Next Week in Lab • Chapter 5, Procedure 1 or 2 • Quiz 5 PreLab is due. Don’t forget to include the Common Shelf • Chemical Data Table! • Quiz 2 on Chapter 5