Caffeine Lab Report PDF

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Caffeine Lab Report...

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Purification of Caffeine Lab Report Purpose: The purpose of this experiment was to extract crude caffeine from coffee or tea and purify that crude sample through various purification methods so as to compare the caffeine content of coffee and tea and compare the purification methods by melting points. Results: Note: I was assigned to use coffee for my experimentation. 1. ● ● ●

Initial Mass of Coffee = 4.0 g Mass of Crude Caffeine = 0.19 g Percent Caffeine Composition = [(Crude Caffeine Mass)/(Coffee Mass)]*100 = [(0.19 g)/(4.0 g)]*100 = 4.75% Caffeine by Mass

TABLE 1: CLASS DATA FOR PERCENT CAFFEINE BY MASS Coffee Initial Mass (g)

AVERAGE

Mass Crude Caffeine (g)

Percent Caffeine by Mass

4.05

0.11

2.72

4.00

0.05

1.25

4.05

0.30

7.41

4.00

0.12

3.00

4.02

0.22

5.47

4.08

0.22

5.39

4.00

0.32

8.00

4.00

0.19

4.75

4.03

0.19

4.71

Tea Initial Mass (g)

AVERAGE

2.

Mass Crude Caffeine (g)

Percent Caffeine by Mass

4.00

0.21

5.25

4.00

0.06

1.50

3.99

0.14

3.51

4.00

0.11

2.75

4.00

0.29

7.25

4.03

0.13

3.23

4.01

0.24

5.99

4.00

0.17

4.25

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One Teaspoon of Coffee = 2.0 to 2.5 g. Given that our class average was 4.71% mass caffeine by mass, one teaspoon coffee contains 0.094 to 0.12 grams of caffeine. One Teaspoon of Tea = 0.7 to 0.8 g. Given that our class average was 4.25% mass caffeine by mass, one teaspoon of tea contains 0.0030 to 0.0034 grams of caffeine; this value is much less than what was calculated for coffee, however this discrepancy is largely due to density of the two compounds, and not percent composition of caffeine.

Discussion: 1. Purity of Caffeine/Method

Melting Point

Crude; No Purification

221.1-223.3 ℃

Pure; Sublimation

223.8-236.1 ℃

Pure; Column Chromatography and TLC

234.8-235.6 ℃

LITERATURE PURIFIED CAFFEINE (1)

235 ℃

Given that caffeine’s literature melting point is 235 °C (1), we can see that our sample’s melting point became progressively centered around 235 °C. This suggests that the purity of the caffeine became progressively greater, as melting point is a physical property of compounds and a theoretical caffeine sample that is perfectly pure should have little to no deviation from its literature melting point of 235 ℃. Thus, our caffeine was most pure after column chromatography and it is therefore a more effective method for the purification of caffeine. In terms of physical properties, the caffeine I attained from sublimation had a bit of yellow/brown. This suggests there were some impurities in the caffeine, as pure, solid caffeine is white in appearance (1). 2. The three methods used for purification of caffeine in this lab were liquid-liquid extraction, sublimation, and column chromatography. They all have their strengths and weaknesses as purification methods, as listed below: ●

Liquid-Liquid Extraction: ○ Strength: Separates an impure fluids into two distinct fluids with different properties, thereby casting a dividing line between impurities. Therefore although the remaining fluid may still have some impurities, a large category of possibilities can be ruled out. (2) ○ Weakness: Leaves behind any impurities that share the solubility property with the desired compound that initially split the solution. (2)

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Sublimation: ○ Strength: Highly concentrates the desired compound into tiny crystals. (3) ○ Weakness: Potential to lose a lot of product if done incorrectly, assumes impurities do not share a similar sublimation property with the desired product. (3)

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Column chromatography: ○ Strength: Can be performed on various volumes and on various products. Almost any organic compound can be purified this way, ranging from milligram to multigram scale. (4) ○ Weakness: Takes a long time and can be done poorly if the column is not constructed properly (each layer being flat and relatively undisturbed). (4)

3. There exist three similarities between TLC and column chromatography: I) Both move a compound through a stationary phase based on the affinity for mobile and stationary phases of the compound (definition of chromatography) (4). II) Both use a solid (silica gel) as the stationary phase (4). III) Both use a liquid absorbent (EtOAc). 4. Methods for purifying caffeic acid by recrystallization: a) Place the crude caffeic acid into a reasonable amount of HOT water/ethanol mix (5) in a beaker and add sufficient HCl for the caffeic acid to precipitate out. The solution should be completely dissolved in just enough solution to dissolve it. If insoluble impurities remain, remove them by hot filtration (step b). b) Vacuum filter with hot water/ethanol mix, collecting the solution that passes through the filter, keeping the solution hot as it passes through, rinsing the filter with hot water/ethanol mix. c) Note: if any insoluble impurities. d) Transfer the vacuumed solution to a beaker and cool it slowly to room temperature, making sure to not go too fast so the pure crystals can form. e) Place the beaker in an in an ice bath until noticeable crystal structures form. f) Now cold vacuum filter the solution, collecting your purified product on the filter paper. Works Cited 1. “Caffeine.” National Center for Biotechnology Information. PubChem Compound Database, U.S. National Library of Medicine, pubchem.ncbi.nlm.nih.gov/compound/2519#section=Melting-Point 2. “Design Principles for Liquid-Liquid Extraction.” AIChE, 21 July 2016, www.aiche.org/resources/publications/cep/2015/november/design-principles-liquid-liquid -extraction. 3. “The University of Chicago Organic Chemistry Laboratory Manual: Experimental Procedure—Part 1: Extraction and Sublimation”, Great River Learning, May 2018.

4. “Separation techniques: Chromatography” Northern clinics of Istanbul vol. 3,2 156-160. 11 Nov. 2016, doi:10.14744/nci.2016.32757 5. “Measurement and Correlation of the Solubility of Caffeic Acid in Eight Mono and Water + Ethanol Mixed Solvents at Temperatures from (293.15 to 333.15) K.” NeuroImage, Academic Press, 24 Oct. 2016, www.sciencedirect.com/science/article/pii/S0167732216325600?fbclid=IwAR2gqPrgZlG ohdbiazEJCsk8AC2lNtx4_3svjr5krNHplc1qCLO8n9Ot4F0. ...