Look at Figure 31.2 in the Procedure section. Note the position of the layers in
ID: 1054673 • Letter: L
Question
Look at Figure 31.2 in the Procedure section. Note the position of the layers in the separatory funnel. What does this say about the relative densities of the water and the dichloromethane? What gives tea its brownish color? How does adding the anhydrous sodium sulfate to the dichloromethane solution remove water? If the above step was omitted in the isolation procedure, how would this be reflected in the yield calculation. A student used 8.23 g of tea leaves in the experiment. How much caffeine is expected, assuming all the caffeine is extracted?Explanation / Answer
Lab
1. The density of dichlormethane is greater than the density of water. Dichloromethane with two Cl in it is heavier than water and hence in the separatory funnel, dichloromethane would be the lower layer. Water is the upper layer.
2. Tea is brownish is ccolor due to the presence of tannin, a bitter polyphenolic molecule.
3. Adding anhydrous sodium sulfate absorbs water from the dichlormethane layer and thereby making the organic layer water free.
Na2SO4 (anhydrous) + nH2O ---> Na2SO4.nH2O (hydrated)
4. If step 3. is avoided, the water present in dihchloromethane would pass on to the final product and thus, the yield of final compound thus calculated would be greater than the actual yield.
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