Caffeine Lab Report PDF

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Introduction The purpose of this experiment was to learn several basic techniques of organic chemistry that will be used throughout the course. The techniques learned were used in the context of separating caffeine from tea. This experiment used the techniques of extraction, filtration, and evaporation of a solvent, and included methods of drying compounds. For this experiment, it was important to know the contents of tea and what potential problems other compounds in the tea could cause. Tea contains caffeine, which is closely related in structure to the heterocyclic bases guanine and adenine that is found in the DNA. Tea is stronger than coffee in the sense that most tea has 3% to 5% caffeine by weight, whereas most coffee beans only have 2% caffeine by weight. Knowing the approximate caffeine amount in the tea can help us make an educated guess on the expected amount of caffeine that would be recovered from the tea as a crude solid. A potential problem of extracting caffeine from tea is that a large class of weakly acidic molecules called tannins also dissolve in the hot water. Therefore, it was important to add calcium carbonate to the water so that the tannins to precipitate and leave the aqueous solution. Experimental Procedure The first step was to weigh out 9 to 10 grams of tea. The measurement that was taken for this experiment was 9.011 g of tea. Using the calculation of 5% caffeine by weight, the expected amount of recovered caffeine was 0.45 g. Then, 4.8 g of calcium carbonate is added and 125 mL of water is poured over the tea and calcium carbonate. After it was all mixed together, the mixture was boiled for 15 minutes, and then cooled down to 55 degrees C. After that, the first technique to be implemented was using the vacuum filtration apparatus to filter out the calcium carbonate and tannins. Then the filtered solution is cooled to around 15 to 20 degrees Celsius in

an ice-water bath, and the tea solution is poured through a 125-ml separatory funnel, along with 15 mL of dichloromethane to the funnel. Once the dichloromethane was added, the separatory funnel is continuously inverted to create separation. Then the two layers are separated and the dichloromethane layer is drained into an Erlenmeyer flask. This is done twice. The dichloromethane that is added to the filtered solution is used to react with the caffeine to separate from the tea solution. This process is done three times to purify the dichloromethane layer. Then anhydrous magnesium sulfate to the dichloromethane solution. The anhydrous magnesium sulfate is used to dry the solution and leave crude caffeine after being dried with a rotary evaporator. Results/Calculations The theoretical yield of crude caffeine using black tea was 5% of the weight of the teas that was used. This translated to about 0.45 g of caffeine, using 9.011 g of black tea to start with for the experiment. The amount of calcium carbonate that was used was 4.81 g. After the procedure was complete, our crude caffeine that was recovered was 0.052 g. Mass of empty round-bottom flask: 57.400 g Mass of round-bottom flask containing crude caffeine: 57.452 g

Percent Yield:

0.052 g Caffeine Recovered 0.45 g Theoretical Caffeine Recovered

x 100% = 11.56% yield

Discussion and Conclusion At the conclusion of the experiment, our data and observations show that only 11.56% of the theoretical amount of crude caffeine was recovered. This is quite a low percent recovered, which points to signs of error during the experiment. The most likely explanation for this is that

caffeine was lost in any of the techniques that were performed during the experiment, but more so during the vacuum filtration. The tea that contained the caffeine may not have been boiled long enough, which didn’t allow all of the caffeine to steep into the water. After boiling, a filter was used to separate the aqueous solution from the loose tea, which left only a small amount of caffeine in the aqueous solution. During the experiment, all steps in the procedure were followed as accurate and precise as possible, so there is a smaller chance that caffeine could have been lost in the other techniques. When the dichloromethane was added into the separation flask, one warning of losing caffeine was that an emulsion layer could be formed. However, the technique of inverting the flask and separating the two layers was done correctly, as there was a little to no emulsion layer that was formed. It is also highly unlikely that any caffeine was lost during the rotary evaporation. This points back to the main source of error, which was not letting the tea boil for longer in order to maximize the amount of caffeine in the aqueous solution. It could also be that we did not have the tea boiling hot enough. The procedure called for boiling just to the point where it was boiling gently, but instead that could have been taken as simmering the solution. This was probably why there was a low percent yield of caffeine. Besides the low percent yield of caffeine, the experiment went well and ran smoothly. The measurements of all compounds used were very precise, and the techniques used were also carried out in the correct manner....