a) In an isolation of caffeine from tea experiment, students try to find out the

Question

a) In an isolation of caffeine from tea experiment, students try to find out the ratio of grams of caffeine per gram of black tea leaves.However most of the students find lower ratio than the published value. Give at least two reasons for this discrepancy. (Dichloromethane is used in the experiment)

b) On the other hand when students calculate grams of caffeine per liter of black tea (not the leaves), most of them find higher results than the published value. Give at least two reasons for this discrepancy.

Explanation / Answer

a. Actually the black tea leaves contains maximum part cellulose along with desired caffiene and other phenolic compounds (tannins). Therefore overall if we compare the yields of caffine in per gram of black tea leaves then its ratio will be lower. The other factors is due to solubility of caffine in water also being an organic compound there is possibility that all the amounts present in te leaves may not be dissolving in water so some amount must be present in the solid parts that will be kept aside.

B. During extraction, when this solid part (cellulose) gets removed and only aqueous part (black tea) remains there then it contains only caffine, tennins so now its relative amount will increase. second reason of getting higher value could be due to amount of water present along with caffine. Due to that its observed amount appears higher then calculated one.

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