2 The liquid-li uid having different dens e liquid-liquid extraction process aen

Question

2 The liquid-li uid having different dens e liquid-liquid extraction process aends on two solvents be immiscible with each other and ferent densities a. What solvent will be used to extract caffeine from the aqueous tea layer? b. Record the density of this extraction solvent: c. Record the density of water d. Which one will be the lower layer in the separatory funnel? e. What is the purpose of adding sodium chloride to the aqueous tea mixture? f. What is the purpose of adding sodium carbonate to the aqueous tea mixture? (refer to physical constants sheet if necessary) a. Ethyl ether and water: b. Ethanol and water: c. Chloroform and water what is meant by ‘drying, an organic layer? 3. Among the following solvent pairs, which layer would be on top? Or would they be miscible? 4, 5. Recrystallization is one way to purify a solid compound. Vaporization of a solid followed by the condensation (or deposition) of the vapor back to the solid phase is another method. Specifically, the conversion of a solid directly to the gaseous phase is called

Explanation / Answer

2.

Extraction is one of a methods used for the separation of organic compound from a mixture of compound. The solubility of caffeine in water is 22mg/ml at room temperature and 670mg/ml at 100°C. For extraction of caffeine, (a) dichloromethane is used as organic solvent to extract caffeine from aqueous extract. This is because caffeine is more soluble in dichloromethane (140mg/ml) than it is in water (22mg/ml). Dichloromethane and water are immiscible each other. Densities of these solvents are also different. (b) Density of dichloromethane is 1.33 g/cm3 and for (c) water is 1 g/cm3. So (d) dichloromethane layer will be settling under the water layer in the separating funnel. We can collect the dichloromethane layer from the bottom. Water and dichloromethane is slightly soluble in each other. If you add some sodium chloride, again density changes will occur so we (e) can completely take out the dichloromethane from water layer. If any residual water will remain the organic layer, anhydrous sodium sulphite is used for the removal of water from organic layer. Anhydrous sodium sulphite is insoluble in organic solvent and will absorb water.

  In the extraction process of caffeine, there is a chance of mixing of tannins in the solution. (f) The tannins that are slightly soluble in dichloromethane can be eliminated by converting it to their salts by adding sodium carbonate. So it will remain in the water.

3.

a. Ethyl ether and water = ethyl ether will be on the top and water will be below. Because density of ethyl ether is lower than water.

b. Ethanol and water = Ethanol and water are miscible each other so it will not form any layer.

c. Chloroform and water = Water will be at top and chloroform will be at bottom. Because the density of chloroform is higher than water.

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