During recrystallization, an orange solution of a compound in hot alcohol was tr

Question

During recrystallization, an orange solution of a compound in hot alcohol was treated with activated carbon and then filtered through fluted paper. On cooling the filtrate gave gray crystals, although the compound was reported to be colourless. Explain why the crystals were gray and describe steps that 2. you would take to obtain a colourless product. The solubility of compound ethanol is 0.8 g per 100 ml at 0 degree C and 5.0 g per 100 ml at 78 degree C. What is the minimum in ethanol needed to recrystallize a 12.0-g sample of compound A? How amount of much would be lost in the recrystallization, that is, would remain in the cold solvent? Describe how you would purify p nitrobenzoic from a mixture of 9.0 g of p nitrobenzoic acid and 2.0 g of p nitrobenzoic acid using recrystallization (see Table 3.1). Tell what solvent you would use and how the components would be separated. Assume that 3.0 g of aniline and 4.5 mL of acetic anhydride are used in the preparation of acetanilide (Eq. 3.1). What is the limiting reagent? What is the theoretical yield of acetanilide? What is the per- cent yield if 3.3 g of acetanilide is obtained? Compound B is quite soluble in toluene, but only slightly soluble in petroleum ether. How could these two solvents be used in combination in order to recrystallize Compound B? PRELABORATORY QUESTIONS Describe the requirements for a "good" recrystallizing solvent. How are insoluble impurities removed in a recrystallization? What is the purpose of adding activated carbon to the warm solution during a In most cases, how does the solubility of a solid in a solvent change increasing temperature? What are boiling stones? Why are they used?

Explanation / Answer

2. To remove insoluble impurities during recrystalization, we first heat the compound. After heating and cooling down, crystals are formed which can removed by filtration. If the impurities are still there, again heat the solution. Then filter out the solution before cooling as the insoluble impurities would be suspended hence would be easier to filter off.

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