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Lab section (day, AM/PM)
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Exercise 12: Extraction of Caffeine from Coffee
Introduction
As we have already observed, different solutes exhibit different solubilities depending
upon the solvent used. An ionic compound (a compound that contains a metal and a non metal)
is typically held together by an ionic bond (an electrostatic attraction due to electron transfer due
to large differences in the electronegativities of the metal and non metal elements). As such,
ionic compounds are typically soluble in ionic or strong polar liquids. An organic compound (a
compound containing carbon and other non metal elements), on the other hand, is typically held
together through non-polar or weakly polar covalent bonds (bonds formed through the sharing of
electrons due to the fact that carbon and other non metals have similar electronegativities). As
such, organic compounds are typically soluble in non polar or weakly polar solvents.
Coffee is a solution that contains a mixture of both ionic and covalent compounds in
water (recall water is a good solvent for ionic and polar covalent compounds because of its
dipole). One component of interest in coffee is caffeine. Caffeine is an organic compound. As
such, it should be more soluble in organic (non-polar or weakly polar) solvents that in water (a
very polar solvent).
In this experiment, a non polar solvent will be added to a coffee solution. The caffeine,
which is more soluble in the non polar liquid than in water, will dissolve out of the water and
dissolve into the non polar liquid. The non polar liquid will be evaporated leaving the extracted
caffeine behind. More interesting reading on caffeine can be found at
http://en.wikipedia.org/wiki/Caffeine.
CH3
N
N
N
N
H3C
O
CH3
O
Caffeine
Procedures
1. Add 100 mL of coffee to a clean, dry 250 mL beaker.
2. Add about 2 grams of Na2CO3 to the coffee in the Erlenmeyer flask and swirl until the
Na2CO3 dissolves.
3. Add 25 mL of CH2Cl2 to the Erlenmeyer flask and swirl for 10 minutes.
4. Allow the solution to stand untouched until two separate layers form. The top layer is the
caffeine free aqueous layer, while the bottom layer is CH2Cl2 with caffeine dissolved in it.
5. Pour off as much of the top coffee layer as you can without losing any of the CH2Cl2 layer.
6. Using a pipet, transfer the bottom layer (the CH2Cl2 layer) into a small beaker (be careful not
to include any of the remaining top layer). Add a scoop of anhydrous Na2SO4 to the small
beaker containing the CH2Cl2.
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Lab section (day, AM/PM)
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7. Measure and record the mass of a clean, dry evaporating dish.
8. Set up a hot water bath as shown by your instructor.
9. Using a pipet transfer the CH2Cl2 from the beaker to the evaporating dish (leave the Na2SO4
behind).
10. Place the evaporating dish on the hot water bath and heat until all the CH2Cl2 has
evaporated.
11. Remove the evaporating dish and allow it to cool to room temperature.
12. Measure and record the mass of the evaporating dish and caffeine.
13. Record the appearance of the caffeine (pure caffeine is a white, crystalline solid).
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Data Sheet for Exercise 12:
Lab section (day, AM/PM)
Extraction of Caffeine from Coffee
Mass of the evaporating dish
_________________ g
Mass of the evaporating dish and caffeine
_________________ g
Mass of caffeine
_________________ g
Appearance of the caffeine:
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