Question

If each bag of Lipton black tea contains 55 mg of caffeine, what is the maximum amount of caffeine that you could extract from one using our procedure? Assume one bag and 40mL of tea-water at the end of initial solid-liquid extraction. The partition coefficient (K) for caffeine in methylene chloride is 7.2.

How much caffeine could be extracted using our procedure if we had used ethyl acetate (K = 2.0) instead of methylene chloride? Explain why the amount does or does not change.

Step 1. Solid–liquid Extraction - Day 1 Add ~500 mg sodium carbonate, ~40 mL water, a few boiling chips, and one tea bag to a 150 mL beaker. Heat and gently boil the tea solution for ~20 minutes with occasional stirring. Allow the tea to cool and squeeze the tea bags gently with a flat spatula against the sides of the beaker to maximize your extraction. Try not to rip the tea bag. Transfer the tea solution to several 15 mL centrifuge tubes and centrifuge for 2 minutes.9 Filter the tea solution under vacuum into a 50 mL filter flask using a Büchner funnel fitted with filter paper. Do this in the 8 You can identify the layers by density or by adding a drop a water and observing in which layer it dissolves. 9 Do not adjust the centrifuge settings.

Step 2. Liquid–liquid Extraction - Day 2 All methylene chloride must stay in the fume hood to minimize unnecessary vapor exposure. Add the ~40 mL of filtered tea solution from day 1 to a 60 mL sep. funnel in the hood. Add ~5 mL of methylene chloride. Cap the sep. funnel and gently shake, remember to vent into the hood. Stop shaking and allow the two layers to separate, ~ 5 min. 10 Collect the clear organic solution in a clean vial; leave behind any emulsion for further extraction. Extract the aqueous tea solution with once more with 5 mL of methylene chloride. Collect the clear organic solution and combine with the first extraction. Next, collect any emulsion into a clean centrifuge tube. Add 2 mL of water, cap, and centrifuge for 2 minutes. Use a pasteur pipette to collect the clear organic layer and combine with the previous extractions. Dry the combined organic layers with magnesium sulfate. Add a few boiling chips to a 60x15 mm petri dish with cover11. Tare the combined dish, cover and boiling chips. Tare the cover separately. Gently clamp a filter pipette (prepared in E0) over the petri dish bottom and transfer the dried methylene chloride solution into the top of the filter pipette using a second pipette. Rinse the solid magnesium sulfate with two 1 mL portions of methylene chloride and filter the washes into the dish as well. Place the petri dish containing the methylene chloride on a warm hot plate in the hood and set it to about 70°C. Several petri dishes can share the same hot plate. Once the solvent has evaporated, allow the dish to cool and replace the cover. Weigh the petri dish and calculate the amount of crude caffeine obtained. The amount will be small.

PART C Sublimation - In the hood, place the covered petri dish containing the crude caffeine directly on a hot plate. Place a 400 mL beaker ice-bath on top of the petri dish cover. Set the hot plate to ~ 350°C. After ~10 minutes, you should see white solid adhered to the cover of the petri dish. Leave the petri dish on the hot plate, replenished the ice bath and turn off the hot plate. Let everything cool slowly on the hot plate until the petri dish is cool (20-30 minutes). Remove the beaker and wipe water from the petri dish. Allow the petri dish to equilibrate to room temperature and carefully record the mass of the petri dish cover and caffeine crystals. Replace the cover and store it in your lab drawer to be analyzed in the next experiment. Use a little parafilm around the edges to minimize caffeine spills

Answer 1