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Question

y lextLIt ara.. No Spac. Normal Heading 1 Heading 2 Heading 4 Heading 5 Paragraph color (4) Nile recorded some original data for this lab: Approximate Weight of tea used: Caffeine's literature Mp: -5.02- 236 Weight of crude caffeine: Mp Crude: Weight of recrystallized caffeine: 40.0 mg Mp. of the crystal Recrystallized: 233.7-235.2 °c 50.0 mg 230-240 °c Answer following questions (a) What is the percent recovery of recrystallized caffeine? (b) What is the percent recovery from tea leaves? (c) Briefly discuss the melting points of both the crude and recrystallized caffeine relative to the literature value. Why the melting point of Nile's isolated caffeine was lower than the literature value. Considering the melting point range of the recrystallized caffeine, briefly comment its purity and tell what may be a good method for further purification

Explanation / Answer

1 (a) Percent recovery of recrystallized caffeine = (Mass of recrystallized caffeine/mass of crude caffeine) x 100%

= 80 %

(b) Percent recovery from tea leaves = (Mass of recrystallized caffeine/mass of tea) x 100%

= 0.796 %

(c) Due to the presence of impurity, the melting point temperaure of crude caffeine was lesser than that of pure caffeine.

Recrystallized caffeine was not 100% pure, so it also had lesser melting point compared to the literature value.

If the impurity is volatile, further purification can be carried out by sublimation under vacuum.

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