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Determining the Relative Caffeination of Decaf Teas

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David Henrich

on 6 June 2014

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Transcript of Determining the Relative Caffeination of Decaf Teas

By David Henrich and Ligia Brolo
Determining the Relative Caffeination of Decaf Teas
To determine the relative caffeination of various decaf teas using tannic acid.
-Caffeinated black tea
-Tannic acid
-Decaffeinated black, & green teas
-Distilled water
-Graduated cylinder
-Four tea cups
-Rubbing alcohol
-Masking tape
-Medicine dropper
-Permanent marker
-Four test tubes
-Small metric food scale
Experimental Procedure
Number of grams of tea used in infusion:
Tazo Black Tea (caf): 5.4868 g
Tetley Green Tea (decaf): 5.4906 g
Tetley Black Tea (decaf): 5.4936 g
Bigelow Black Tea (decaf): 5.4798 g

1 Drop Tannic Acid Solution: 500 µl

Number of drops to form precipitate:
Tazo Black Tea (caf):1
Tetley Green Tea (decaf): 16
Tetley Black Tea (decaf): 10
Bigelow Black Tea (decaf): no precipitate was formed after 20 drops
1) Label five teacups with the masking tape and permanent marker as follows: Tazo Caf Black, Tetley Decaf Green, Tetley Decaf Black, and Bigelow Decaf Black.
2) Open the four teabags and place the loose tea leaves of each of the three decaf teas into its corresponding labeled cup.
3)In the fourth cup add the same amount of caffeinated black tea. This tea is the control.
4)Bring distilled water placed in a teapot to a rolling boil and pour it over the teas.
5) Allow the teas to steep for up to an hour to maximize the amount of caffeine that is extracted.
6) Carefully pour 2 ml of each tea infusion into five test tubes and allow the tea infusions to cool.
7) Dissolve 1 g of tannic acid in 1 ml of alcohol, and dilute with distilled water to 10 ml. Prepare this solution fresh.
8) Using a medicine dropper add tannic acid drop-wise to the caffeinated black tea. If a white precipitate forms, caffeine is present. Stop adding the tannic acid! If an excess amount of tannic acid is added, the precipitate will dissolve and disappear!
9) Record the number of drops added until the caffeine was detected.
10) Using a medicine dropper add tannic acid drop-wise to the four decaffeinated teas stopping immediately when or if a white precipitate is seen.
11) Record the results.
It is predicted that if a tannic acid solution is added to decaf tea, then a white precipitate will form, indicating the presence of residual caffeine.
When the experiment was originally performed, the tea that was used had not been steeped adequately to make the reaction take place. Not enough caffeine had been extracted from the tea leaves. The experiment was then repeated on tea that had been steeped for a very long time. When 500 µl of tannic acid was added to the caffeinated Tazo black tea, a white precipitate formed immediately, indicating a high concentration of caffeine. A precipitate formed in the Tetley green tea (decaf) after 8000 µl of tannic acid were added, and a precipitate formed in the Tetley black tea (decaf) after 5000 µl of tannic acid were added. 10000 µl of tannic acid were added to the Bigelow black tea (decaf), but no precipitate was formed, indicating that any caffeine present was negligible. This would indicate that the Tetley green tea (decaf) had the most caffeine left over after the decaffeination process, followed by the Tetley black tea (decaf). The tea with the least caffeine was the Bigelow black tea (decaf). A source of error that can be drawn from this is the fact that different brands of tea were used. Ideally, all the teas that were tested would be from the same brand, but unfortunately, that was not the case this time. Another source of error is the fact that all the teas were not steeped for the exact same amount of time, meaning that more or less caffeine may have been extracted, which could effect the outcome of the experiment. Additionally, the precipitate took a few moments to form, which means that some of the measurements of the number of drops required to form a precipitate could be slightly off if more tannic acid was added while the precipitate was still forming.
The hypothesis was correct in regards to the two Tetley decaf teas, which were found to have some residual caffeine, but any caffeine in the Bigelow decaf black tea was imperceptible by our methods of observation.
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