Summer Research Program for Science Teachers

Eric Paul

Bergen Academies


Activity #2 Related to Natural Products

Activity 1: Operation of the Microwave Oven for Chemistry Experiments

Activity 3: Growing Barley and Detecting the Presence of Amino Acids

Introduction to Activity 2: Natural products are substances produced in living systems that may be useful to humankind, especially in the field of medicine. For example, taxol is a substance derived from Pacific yew trees that has been shown to be effective against certain types of cancer.   The extraction of such substances is necessary before their therapeutic value can be evaluated.

This action plan presents three activities related to natural products. One of these is the extraction of a natural product, caffeine, from tea leaves. This has been chosen since the starting ingredients are relatively easy to come by, and the student will still find a reasonable level of challenge. The microwave oven was chosen to provide energy for heating the tea bags, to emphasize the importance of the microwave oven in the field of organic chemistry. Microwave-assisted chemical reactions are increasingly important, especially for organic chemistry. Many chemical reactions that used to take hours now take minutes or seconds with the use of microwave techniques. A simple demonstration of the microwave is included in the action plan. A third activity is the growing of barley under controlled conditions, since it is often necessary to grow plants (or animals) to provide raw material from which natural products can be extracted. The growing of plants offers ample opportunity for open-ended activities


II.  Extraction of Caffeine from Tea Leaves

Caffeine is a natural product found in coffee and tea.  It is chosen here because it is relatively easy to extract compared to some of the other substances students might be interested in. 

 Objective:  To obtain the greatest number of grams of caffeine from four bags of tea.

[9-12 Content Standard E- Abilities of technological design]


Materials and Equipment


rotovapor machine or hot plate                         three 400-mL beakers

1000-mL beaker                                                basin for ice

ice (cubes or crushed)                                       Earl Grey tea (or any tea containing caffeine)

petri dish                                                            100-mL graduated cylinder

glass stirring rod                                                NaHCO3

500-mL separatory funnel                                 ring stand with ring

expendable rubber tubing                                  dichloromethane

regular funnel                                                     hood

goggles                                                                250-mL Erlenmeyer flask

filter paper                                                          Na2SO4 (anhydrous)

rubber tubing                                                      aspirator or vacuum setup

round-bottom flasks                                           gloves

organic waste can                                               kitchen mitts

stirring rod

[Teaching Standard D- Make accessible science tools]


Before conducting this experiment, ensure individuals (such as wearers of pacemakers) who should not be near operating microwave ovens are out of the room.


(Students perform this activity in groups of four or five.  Every member has a lab book in which procedures, observations, and data must be recorded.  The four members of each group have specific tasks to do.  Task #1 is safety engineer, the person who directs the others and reminds them to wear goggles and to follow other safety procedures, task #2 is balance technician, task #3 is microwave oven technician, and task #4 is “setups technician,” who sets up various pieces of equipment, such as the separatory funnel.  For five-member groups, there is a director distinct from the safety engineer. ) [Teaching Standard E- Nurture collaboration among students]


1.  Put on goggles.


2.  Set up the separatory funnel in advance.  Place the ring stand in the hood.  It is desirable to place rubber bumpers on the iron ring so as to protect the glass from breakage.  The rubber for this will come from expendable rubber tubing.  Cut a short section of tubing, then cut it open lengthwise, so that it can be wrapped around the ring.  Place these bumpers approximately 120o from each other on the iron ring, and this will protect the funnel against damage when it is placed in the iron ring.


3.  Prepare a basin of ice for cooling the beaker of tea later.


4.  In a hood start heating the water in the rotovapor machine (or in a beaker on the hot plate, if there is no rotovapor machine).


5.  The objective is to produce the greatest number of grams of caffeine per tea bag.  Students are given this objective in advance, so they can do research in the library, on the Internet, and by talking to experts, to identify promising teas for extraction of the most caffeine.  [9-12 Content Standard A- Identify questions/concepts that guide inquiry] Start with four tea bags. 


6.   Four tea bags are to be massed.  It is important that tea leaves not leave the bags, so the bags should not be punctured, but strings and tags should be cut off and paper wrappers removed before massing. 


7.  Using the graduated cylinder, measure 100mL of distilled water into a 400-mL beaker.


8.  Mass 2.0 g of NaHCO3 and use glass rod to stir into beaker of water.


9.  Submerge tea bags in the solution in the beaker.


10.  Place a clean, dry petri dish on the top of the beaker to prevent splattering.  Thus covered, the beaker should be placed on the turntable of the microwave oven.  Set microwave oven for 100% power for a duration of 1 minute.  Then start the oven.  After one minute, if boiling is observed, then go to next step.  If no boiling is observed, irradiate for another 1-minute interval, and continue to do so in 1-minute intervals until boiling is observed.


11.  Decant the liquid to a 400-mL beaker and examine the liquid to see if any tea leaves have escaped the bags.  If the liquid is free of tea leaves, then proceed to the next step.  Otherwise, repeat steps 6 through 11.


12.  Cool the tea by setting the beaker in a basin of ice.


13.  Ensure separatory funnel valve shut.  Using an ordinary funnel, pour the tea into the separatory funnel.


14.  Put on gloves.


15.  The separatory funnel should be placed in the hood if it has not been already. 


16.  Using a graduated cylinder, measure 25 mL of dichloromethane.  Dichloromethane and the tea mixture can form an emulsion difficult to separate if allowed to be agitated, so slowly  pour the dichloromethane into the separatory funnel. 


17.  Avoid shaking the separatory funnel too vigorously.  Remove the top of the separatory funnel (if it is not already removed), and gently tilt the mixture back and forth, or else a bothersome emulsion will form. [9-12 Content Standard B- Chemical reactions/Properties of matter]


18.  After the bottom layer is removed from the separatory funnel, it must pass through a drying agent (such as Na2SO4).  The purpose of this second filtration setup is to remove any H2O from the bottom layer.  Set up the Erlenmeyer flask close by the separatory funnel, and place a conical funnel in the Erlenmeyer flask.  Line the conical funnel with filter paper.  Place a small amount of dichloromethane on the filter paper so that it will adhere to the sides of the funnel.  This setup will be used in the next step to remove Na2SO4.   


19.  Place an Erlenmeyer flask under the separatory funnel to catch the bottom layer.  Gently open the valve to allow only the bottom layer to pass through.  Turn the valve to the shut position before any of the top layer passes through.  Add anhydrous Na2SO4 to the liquid and stir.  Pour the contents of this flask through the paper-lined conical funnel so as to remove the Na2SO4.


20.  Set up the rotovapor machine.  [9-12 Content Standard E- Understandings about science and technology] (Omit this step if you will be using a hot plate instead.)  Ensure tubing is hooked up for aspirator (or vacuum) and for cooling water, including a secure hose leading to a drain.  Turn on the cooling water.

Transfer the filtrate to a round-bottom flask, and attach this to the appropriate end of the rotovapor machine.  Ensure a receiving flask is also in place.  Apply a partial vacuum by opening the vacuum valve, or, if you lack a vacuum valve, set up an aspirator to provide a partial vacuum.  Shut the valve at the top of the condenser.  Start the rotation of the sample flask.  Gently lower the sample flask into the water, but if the solvent boils too violently, elevate the sample flask and lower the temperature of the water, then try again. 


21.  If you lack a rotovapor machine, do the following:  set up a heating bath in a 1000-mL beaker on a hot plate in the hood.  Place the filtrate in an Erlenmeyer flask, and using kitchen mitts, lower the Erlenmeyer flask until its bottom is in contact with the hot water. This will provide heat to evaporate the solvent.  Any time the filtrate begins to boil, lift the flask, then lower it again.  Eventually the solvent will be driven off and a solid will be left behind.


22.  With a spatula, remove the solid left behind and mass it.  This solid is principally caffeine.  Record this for comparison with other teas.


23.  If this is the last tea sample to be tested, then commence clean up.


Repeat the experiment with other brands of tea to see which is has the most caffeine per bag.  The number of tea bags tested at a time may also be changed. [Content Standard Unifying Concepts- Change, constancy, and measurement]


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