After we removed the solution from the hot plate and Oltered out the carbon, itbegan crystalizing. The longer the solution cooled, the more crystallizationoccurred. After 5 minutes crystallization was complete.1. What would it mean if the melting point had a wide range in temperature ratherthan a narrow range of one to two degrees? When no single solvent can be found that meets all of the criteria for crystallization, it may be possible to use a mixed solvent. A pair of solvents is chosen: one in which the compound is soluble (called the "soluble solvent"), and one in which the compound is insoluble (called the "insoluble solvent"). The two solvents must be miscible in one another so that their solubility with one another does not limit the proportions used. Table 3.2 shows a list of common mixed solvents used in crystallization. To perform a crystallization using a mixed solvent, the solid to be crystallized is first dissolved in the minimum amount of hot "soluble solvent", then hot "insoluble solvent" is added dropwise until the solution becomes slightly cloudy. An additional small portion of hot soluble solvent is then added to clarify the solution, and the solution is set aside to slowly cool and crystallize. A diagram describing this process is shown in Figure 3.13. Although this procedure can produce good results, when possible it is often best to use a single solvent for crystallization. As a mixed solvent is heated, the composition can change as the solvents evaporate at different rates, which can affect the solubility of the compound in the mixed solvent. Also, crystallizations from mixed solvents sometimes "oil out", where the dissolved compound comes out of solution above its melting point and forms a liquid instead of a solid. To test a mixed solvent for crystallization, use the procedure that follows. This process is demonstrated by crystallizing trans-cinnamic acid from a mixed solvent of water and methanol (Figures 3.14 + 3.15).
Get the answer to your homework problem. Try Numerade free for 30 days
Brent S. Chemistry 101 12 months ago
'In which of the following cases would recrystallization be favored over extraction when purifying mixture of two solid compounds? When the desired compound is freely soluble in the solvent pair. at all temperatures_ II When significant difference in pKa exists between the two compounds_ III: When there is a significant excess of the undesired compound. and B. Il C. Iland E. /, Il, and IIl F: None of the above and'
Get the answer to your homework problem. Try Numerade free for 30 days
Weber State University
Amy S. Chemistry 101 1 year ago
You have just made new compound in the lab and need to choose good solvent for your recrystallization experiment: From the data collected below; which solvent from the list is best suited for this experiment? Solvent Solubility at boiling Solubility at 0"€ (g/L) (g/L) 17 35 90 30 100 95 15 80 70 30 15 Hexanes Methanol Ethanol Dichloromethane Water Diethyl Ether Dichloromcthanc Ethanol Hexancs Watcr
Get the answer to your homework problem. Try Numerade free for 30 days
Russell N. Chemistry 101 11 months, 3 weeks ago
'In which of the following cases would recrystallization be favored over extraction when purifying mixture of two solid compounds? When the desired compound is freely soluble in the solvent pair. at all temperatures_ II When significant difference in pKa exists between the two compounds_ III: When there is a significant excess of the undesired compound. and B. Il C. Iland E. /, Il, and IIl F: None of the above and' |