Organic Chemistry Lab 315 Fall, 2016 Lab does not meet on Tues., Oct. 11. (Monday classes meet). DUE DATES Today At beginning of lab Identification of an Unknown Report Problem #1, Part II, Spectroscopy Problem Set At end of lab -- copy of laboratory notebook pages for today's experiment (do not turn in your pre-lab notes or in-class notes)
Next Week (when we meet) Part II, #2 Spectroscopy Problem Set Extraction of Caffeine Report Report Notes Last Week Pay attention to significant figures in calculations. Review them if necessary. You cannot add a digit to an experimentally determined mass. Example: mass = 1.254 .001 and for some reason you add 0
and use 1.2540. You would not add a 2 for example why would you add any digit to the data? Properly labeled vial example in Pavia. It must include the melting point range you always report ranges (and it is an indication of purity). In Lab Today Learn the new technique of extraction. Drying organic solvents (See p. 697 in Pavia). Experiment Notes
Beaker containing dissolved caffeine and insoluble binder Funnel with glass wool as filter Separatory funnel supported on iron ring on ring stand Stopcock closed Beaker underneath just in case Experiment Notes
Beaker containing dissolved caffeine and insoluble binder Separatory funnel with stopper Funnel with glass wool as filter Aqueous layer on top Separatory funnel
supported on iron ring on ring stand Methylene chloride layer on bottom (contains caffeine) Stopcock closed Beaker underneath just in case Drain off CH2Cl2
bottom layer into beaker Total 3 extractions (8 ml x 3) Experiment Notes Extractions in a Separatory funnel Add liquids using a glass funnel in order to not contaminate the neck of the sep. funnel. Remove stopper before separating phases. After replacing the stopper, turn the sep. funnel
upside down to vent. Repeat if audible/visible gas escapes. Shake/swirl gently, but thoroughly, to mix the immiscible liquid phases. An emulsion may form in this experiment. Caffeine is in the bottom CH2Cl2 layer. Drain bottom layer through stopcock into 100 ml beaker. [This is one extraction.] Add additional CH2Cl2 (using glass funnel) from top. Extract with CH2Cl2 three times total, combining all extracts in beaker. Stopcock should be closed!
Experiment Notes Drying Organic Solvents There will be water dissolved in the CH2Cl2 extracts that needs to be removed. Organic solvents are dried by using an anhydrous salt that can absorb the water and become hydrated. See Section 12.9 in Pavia for common drying agents and equations for anhydrous salt hydrated salt MgSO4 + H2O MgSO410H2O When you are ready to dry your solution, bring it to the instructors bench. After drying, decant the solution into a pre-weighed beaker. Experiment Notes
Make sure the balance is displaying .001g Evaporate solvent using a hot plate UNDER THE HOOD. Do not recrystallize caffeine. Weigh the beaker and mostly dry caffeine. Place your caffeine in a properly labeled vial. See Pavia for an example of a correctly labeled vial. Caffeine tablet contains 200 mg of caffeine. The remainder is inert ingredients.
Calculate the % isolation based on the mg caffeine in the 2 tablets. Report for Next Week Report Form in Manual Separation Scheme (flow chart of procedure for separating a pure product from reaction byproducts or mixture impurities). See explanation and example in Manual/class web page. There is no other written report required (major grading will be for the Separation Scheme be sure you understand it).
Report for Next Week Some additives in Vivarin: polyethylene glycol and polysorbate 80 (water-soluble) titanium dioxide and silicon dioxide (waterinsoluble) D&C yellow #10 and yellow #6 aluminum lake dyes (water-insoluble) carnauba wax (water-insoluble) dextrose (water-soluble) Report for Next Week These additives should be included in your Separation Scheme for isolating caffeine from Vivarin tablets. You do not need to find the
structures for these compounds. You can ignore the effect of Na2CO3 on the watersolubility of any of these additives, although Na2CO3 should be included in the scheme. (Na2CO3 was added to the Vivarin-water solution.) Report for Next Week Your Separation Scheme should resemble the one done for isolation of caffeine from tea leaves, shown in class. (It would be helpful if you printed the linked page and brought it to class.) Tea leaves separation Right-click on the hyperlink above, and then choose open hyperlink
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