1. What purpose does sodium carbonate serve during the extraction of caffeine fr

Question

1. What purpose does sodium carbonate serve during the extraction of caffeine front tea leave? 2. What purpose does a 1 -cm layer of anhydrous sodium sulfate in the apex of the funnel serve while transferring the dichloromethane extract into the round -bottom flask? 3. What is steam distillation and why is it i preferred technique to purify high boiling liquid that are water insoluble? 4. the presence of the carbon-carbon double bond in eugenol can be tested using the bromine water test. Write a balanced equation for the reaction involved in this test

Explanation / Answer

1. The sodium carbonate acts as a base - you could use sodium hydroxide instead. When you boil tea leaves tannins dissolve in the water as well as the caffeine. If you do not use a base the tannins will also be extracted into the solvent (i.e. methylene chloride) used in the subsequent extraction . The base converts the tannins into their sodium salts - being ionic these salts are not soluble in solvents like methylene chloride so remain in the aqueous layer during extraction. This allows purer caffeine to be extracted.

2. Anhydrous sodium sulfate is used as a drying agent to remove microscopic amounts of dissolved water in a solvent. It works by chemically reacting with the water by forming its hydrate, which is insoluble preferably in the solvent in this case dichloromethane. This allows one to filter off the crystals containing the water that would otherwise have remained dissolved in the dcm

3.steam distillation is where substance is purified by heating with immiscible substance By heating with immiscible substance, when heated, they both exert independent vapor pressure. steam distillation is an effective way to separate slightly volatile water insolube substance from nonvolatile material. Steam distillation offers an advantage in volatile compounds that are unstable or have high boiling points can codistill with water at relatively low temperatures. This process avoids decomposition that might occur at the normal boiling point of the compound of interest.

4.Eugenol contains a carbon-carbon double bond and an aromatic hydroxyl group called a phenol. These functional groups provide the basis for simple chemical tests used to characterize the clove oil. A solution of bromine (Br2) in dichloromethane decolorizes as Br2 reacts with the double bond to form a colorless compound. The balanced equation for the reaction involved is as follows: C10H12O2 + Br2 + H2O ---> C10H13O3Br + HBr. Some C10H12O2Br2 will form as well.A positive test is the disappearance of the red Br2 color.

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