lab report 03

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Feb 20, 2024

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Nalo Russell Experiment 3 - Caffeine from Tea Fill in the blanks in the given template. Use underlines, boldface, or parentheses to clearly indicate the filled content within the context. Type up the report and save it as one single file in the PDF format. Submit the PDF file by the deadline. Key Observations - The appearance of 7.993 g (amount) of calcium carbonate in 300 mL (volume) of water in a 600-mL beaker: brown, foggy, liquid (color, clarity and form). - 15 (number) tea bags were added into the above mixture. The appearance of the mixture: dark brown, cloudy, and liquid (color, clarity and form). - The resulting mixture was heated at a temperature of ~100 °C for 20 min. (time). - The approximate volume of the final mixture right before being transferred into a separatory funnel: ~200 mL. Its appearance: dark brown, clouding, and liquid (color, clarity and form). - The appearance of the aqueous layer in the separatory funnel after the first round of dichloromethane extraction: translucent, slightly cloudy, and liquid form (color, clarity and form). It is the bottom layer (top or bottom). - The appearance of the organic layer in the separatory funnel after the first round of dichloromethane extraction: translucent, slightly cloudy, and in liquid form (color, clarity and form). It is the top layer (top or bottom). - The appearance of the interface between the organic layer and aqueous layer in the separatory funnel after the first round of dichloromethane extraction: distinct layers, translucent, and sharp form (color, clarity and form). - The appearance of the combined organic layer before being dried with Na 2 SO 4 : cloudy liquid (color, clarity and form). It was then dried with ~ 4 grams of Na 2 SO 4 for 20 min. (time). - Change of the appearance of Na 2 SO 4 (size and form) throughout the treatment: from fine powder/ granular to larger, clumped/aggregated particles. .

- The appearance of the resulting organic layer after being dried with Na 2 SO 4 : colorless (faint yellow), the clarity is clear and in liquid form (color, clarity and form). - The Na 2 SO 4 was removed from the organic layer by filtration . - The crude caffeine was obtained from the organic layer by using a rotary evaporator to remove the organic solvent. - The crude caffeine was transferred to a tared vial with the aid of ~ 20 mL of dichloromethane. - Crude caffeine (dried): amount 0.443 g , color tan , form (and shape) white crystalline powder. - Power of the heating mantel used during the sublimation of the crude caffeine: between 40 - 65 %. - Sublimed caffeine: amount 0.8 g , color yellow(ish) tan, form (and shape) powder some parts were granulated , mp 222 - 227 °C. Results (Show calculations. Assume 45 mg caffeine per tea bag. Apply the significant figure rules) - Theoretical yield of caffeine (mg): 675 mg - Percent yield of the crude caffeine (percent crude yield = amount of the crude/ theoretical yield x 100%): 6.562 %. - Percent yield of the purified caffeine (percent purified yield = amount of the purified / theoretical yield x 100%): 1.1852 %. - Percent recovery yield of the sublimation (= amount of the sublimed / amount of the crude x 100%): 18.0587 %.

Discussion Suggest two major causes including one unavoidable cause for the low recovery yield of the crude caffeine from tea. (1) Incomplete extraction: caffeine extraction from tea leaves may not be thorough due to limitations in the extraction method or conditions, such as insufficient extraction time or improper temperature control. This may have caused a loss of material through (2) Loss during purification: during the purification process, there could have been a loss of caffeine due its solubility in the solvent, absorption into purification apparatus, or a loss of material through transfer during the procedure. Comment on the identity and purity of the purified caffeine based on the melting point of your product in comparison to the melting point reported in the literature. The identity and purity of the purified caffeine can be assessed by comparing its melting point to the theoretical value. My recorded melting point was 222 - 227 °C, which is significantly lower than the expected value of 236- 238 °C. Consistency in the melting point indicates the absence of impurities. However, my melting point deviates significantly from the expectation, which indicates the presence of impurities or a different crystalline compound within the caffeine. Suggest two practical things you could do to improve the recovery yield and/or purity of the caffeine without making any major change to the experimental procedure. (1) Optimize extraction conditions: you can better optimize the extraction parameters with the type of solvent, temperature precision, and extraction time. Experimenting with different solvents, adjusting the temperature, and extending the extraction time can possibly enhance the efficacy of caffeine extraction from tea leaves without altering the fundamental extraction technique. For instance, using a solvent with a higher affinity for caffeine or increasing the extraction temperature slightly within safe limits can improve the overall yield without significant changes to the procedure.

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(2) Implement additional purification steps: incorporating additional purification steps, such as recrystallization or possibly chromatographic methods, can help enhance the purity of the recovered caffeine. Recrystallization involves dissolving the crude caffeine in a minimum amount of hot solvent and then allowing it to slowly cool and crystallize. In this way, promoting the formation of pure caffeine crystals while leaving the impurities behind. Additionally, chromatographic methods like column chromatography or thin-layer chromatography can further separate caffeine from impurities based on tier different affinities for the stationary [hase, improving the purity of the final product without altering the experimental protocol. Post-Lab Questions for Experiment 3 1. n-Butanol is water soluble. But if you add salt to an aqueous solution of n-butanol, you can extract the n-butanol into dichloromethane. Explain how this works. When you add salt to an aqueous solution of n-butanol, the water becomes more polar due to the presence of ions from the salt. This increased polarity of the water phase makes it less favorable for nonpolar compounds, like n-butanol, to remain dissolved in it –– since like dissolves like. As a result, the n-butanol molecules tend to aggregate and separate from the water phase. Dichloromethane is an organic solvent that is immiscible with water and has a high affinity for nonpolar compounds. When you introduce dichloromethane to the salted aqueous solution containing n-butanol, the n-butanol molecules divide with a preference in the dichloromethane phase due to their nonpolar nature. This partitioning occurs also because like dissolves like –– where the nonpolar n-butanol molecules are more soluble in the nonpolar dichloromethane than in the polar water phase. 2. In extraction of an aqueous mixture, an experienced organic chemist would prefer to use a “heavier” organic solvent such as methylene chloride (density > 1) over a “lighter” solvent such as ethyl acetate or diethyl ether (density < 1). This often has little to do with distribution coefficient, volatility, miscibility, or reactivity. The chemist simply wants the organic layer as the

bottom layer in a separatory funnel. Provide two practical advantages of having the organic layer as the bottom layer when conducting Experiment 3 - Caffeine from Tea. Having the organic layer (methyl chloride) as the bottom layer in a separatory funnel during experiment 3 can offer practical advantages: (1) Ease of separation: with the organic layer at the bottom, it is easier to drain and separate it from the aqueous layer. Gravity aids in the separation process, allowing for a cleaner and more efficient transfer of the organic phase to another container. This ultimately minimizes the risk of contamination or loss of the desired product during transfer. (2) Safety considerations: methylene chloride, being more dense than water, tends to remain at the bottom layer, resulting in the reduction of the likelihood of accidental spills or splashes during handling. Overall, this improves safety in the laboratory by minimizing the potential for exposure to hazardous chemicals. Also, if any water accidentally gets into the organic layer, it will remain as a distinct layer at the top, making it easier to detect and remove before continuing with the experiment. 3. The rotavap is not removing the methylene chloride (bp = 39.6°C) from your solution. This often can be attributed to the problem of the vacuum and / or heating of the rotavap. Provide a list of things to check for diagnosis of the cause of the problem. If the rotavap is not effectively removing the methylene chloride from the solution, several factors related to the vacuum and heating of the rotavap should be checked for diagnosis: (1) Vacuum pump operation: ensure that the vacuum pump is functioning correctly. Check for any leaks in the vacuum tubing, connections, or seals. Inspecting the vacuum gauge to confirm that the necessary vacuuming level is being achieved in important for functionality (2) Vacuum control settings: verifying that the vacuum control settings are set appropriately in order to optimize solvent evaporation. (3) Rotavap bath temperature: check the temperature of the water bath in the rotavap. Ensure that it is set to an appropriate temperature for the boiling point of methylene chloride.

Adjust the bath temperature as needed in order to facilitate solvent evaporation without overheating. (4) Bath fluid circulation: ensure that the bath fluid is circulating properly around the condenser to efficiently cool the vaporized solvent. Checking for any blockages in the circulation system that may impede heat transfer is important for proper function. (5) Condenser coolant temperature: Verify that the coolant flow to the condenser is sufficient and that the temperature of the coolant is low enough to condense the methylene chloride vapor efficiently. By systematically checking these factors, you can diagnose the cause of the problem with the solvent removal in the rotavap and take appropriate corrective actions to improve its performance.

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