A student is extracting a caffeine/water solution with dichoromethane. The K val
ID: 478708 • Letter: A
Question
A student is extracting a caffeine/water solution with dichoromethane. The K value is 4.6. If the student starts with a total of 40 mg of caffeine in 2 mL of water) and extracts once with 6 mL of dichloromethane, how much caffeine will be in the dichloromethane extract? Another student also starts with 40 mg of caffeine in 2 mL of water and decides to use three extracts, each with 2 mL of dichloromethane. How much caffeine will be in each extract? How much caffeine total in all three extracts of dichloromethane?Explanation / Answer
2. Extraction of caffeine
let x grams of cafeeine is extracted by 6 ml of dichloromethane
K = 4.6 = (x/6)/[(40 - x)/2]
92 - 2.3x = 0.167x
x = 37.3 mg caffeine is extracted in dichloromethane
3. With three stage extraction
K = 4.6 = (x/2)/[(40 - x)/2]
92 - 2.3x = 0.5x
x = 32.86 mg caffeine is extracted in first stage dichloromethane
K = 4.6 = (x/2)/[(7.14 - x)/2]
16.42 - 2.3x = 0.5x
x = 5.86 mg caffeine is extracted in second stage dichloromethane
K = 4.6 = (x/2)/[(1.28 - x)/2]
2.94 - 2.3x = 0.5x
x = 1.05 mg caffeine is extracted in third stage dichloromethane
Total caffeine extracted = 39.77 mg
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