Need help, please answer of all them. Thank you. attf A mixture is spotted on a

Question

Need help, please answer of all them. Thank you. attf A mixture is spotted on a TLC plate. After developing, a single spot is observed. This spot is almost at the solvent front. How can the separation be improved? 1. a. Use a smaller amount of sample b. Use a larger amount of sample Use a more polar solvent for elution (for TLC analysis) c. d. Use a less polar solvent elution (for TLC analysis) 2. Which of the following statements about extraction is false? a. The b. T extraction solvent should be immiscible with the aqueous phase he extraction solvent should form an emulsion with the aqueous phase The extraction solvent should have a different density than the aqueous p hase c. d. Multiple extractions are more productive than one extraction of the following procedure is incorrect when you crystall compound? 3. Whi a. Using minimum amount of the solvent b. Us c. Using a solvent that dissolves the solid at boiling temperature d. Placing a boiling chip in t e. All of the above ing a solvent that dissolves the solid at room temperature he flask containing the solvent before heating 4. Vacuum filtration is the correct technique for which of the following a removal of decolorizing carbon b. removal of drying agent c. isolation of crystals d. purification

Explanation / Answer

1) TLC is the technique where a mixture of samples is separated based on their interactions with a polar stationary phase (usually silica or alumina) and a less polar solvent (like hexane, heptane, dichloromethane, etc). In TLC, the samples are separated based on the relative strengths of their interactions with the stationary phase particles and the mobile phase particles. The stationary phase is polar and hence, polar molecules adhere to the stationary phase strongly. The less polar molecules dissolve in the solvent and are carried to the solvent front quickly. In this case, the separation can be improved by using a less polar solvent. The sample particles will have poorer interactions with the mobile phase and hence, will spend more time on the stationary phase, i.e, the sample molecules will be retained more and hence, elute slowly. Therefore, (d) is the correct statement.

2) An emulsion is a dispersion of fine droplets of one liquid into another immiscible liquid. In solvent extraction, the organic solvent simply forms a separate layer usually above the aqueous layer, but do not disperse into the aqueous phase. Consequently, the two solvents used in solvent extraction do form an emulsion and therefore, (b) is false.

3) In case of crystallization, a solid is usually dissolved in minimum volume of a solvent such that the solid is soluble in the solvent at high temperatures, but doesn’t dissolve in the solvent at low or room temperatures. If the solid dissolves in the solvent at room temperature, common separation techniques like filtration cannot be used to separate the solid from the solvent. Hence, (c) is the incorrect statement about solvent extraction.

4) Vacuum filtration is the process where a solvent and soluble impurities are removed from a solid by passing the mixture of the solid along with impurities and the solvent through a filtration apparatus. Vacuum is applied to hasten the separation process. Therefore, the correct answer is (d).

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