A student neglected to add sodium carbonate when extracting the tea leaves with
ID: 535479 • Letter: A
Question
A student neglected to add sodium carbonate when extracting the tea leaves with hot water. Yet a very high yield of caffeine was obtained. The crystals melted at 202-214 degree C. Explain. The weight of the purified caffeine is often much lower than the weight of the crude caffeine. Explain why the percent recovery is frequently low. Cholesterol is purified using a hot gravity filtration. Why must the beaker and filter paper be kept hot? ls it better to do two extractions with 10 mL of methylene chloride or one extraction with 20 mL of methylene chloride? Explain. Why is decolorizing carbon (charcoal) used in the purification of cholesterol? Identify all of the functional groups present in cholesterol. Look up the structure of sugar (sucrose). What problems might be encountered in trying to extract caffeine from a soft drink that contains sugar? Library Project: Explain the relationship between excess cholesterol and heart diseaseExplanation / Answer
1. The sodium carbonate acts as a base - you could use sodium hydroxide instead. when you boil tea leaves tannis dissolve in the water as well as the caffeine . if you donot use a base the tannins will also be extracted in to the solvent ( methylene chloride) used in the subsequent extraction . the base converts the tannins in to their sodium salts- being ionic these salts are not soluble in solvents like methylene chloride so reamin in the aqueous layer during the extraction . this allows purer caffeine to be extracted.
2.Purified caffeine is very much just caffeine by itself. crude caffiene contains contaminants, usually other oragano-compounds that were part of the plant the caffiene was extracted from . so, in short, the contaminants add weight to the products .
3. The beaker and filter paper must be kept hot to prevent the mixture from cooling when trasnferring in to the beaker and makes the next step, which is heating the mixture much faster.
4.It is always better to do two extractions with 10 ml of methylene chloride because more extractions results in a higher efficiency of the extraction to produce a more pure product.
5. decolourising carbon is used in purification of cholesterol to filter out the bilirubin pigment so that a purer cholesterol can be obtained.
6. Cholesterol has two types of functional groups. the first one called a hydrocarbon functional group consists of atoms of hydrogen and carbon.In cholesterol, the hydrocarbons connect to form two differnt shapes - rings and chains. the second group called a hydroxyl group, contains one atom each of hydrogen and oxygen.
7.Problems that are encountered are the sugar is soluble in both water and methylene chloride, so it can lead to less pure caffiene product.so, another technique needs to be used to extract caffeine from soft drinks.
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