Question

Which of the following statements is true when considering temperature during a recrystallization? More than one answer may be correct. It is important that the sample is dissolved in just enough hot solvent. Ideally the hot solvent used will keep the impurities dissolved OR not dissolve them at all. Using ice to cool the sample will speed up the crystallization process so that large crystals will be formed. Enough cold solvent should be added to dissolve the sample BEFORE heating it past its boiling point.

Answer 1

Temperature is crucial in recrystallization process. A hot solvent should be used to dissolve the sample, and enough cold solvent should be added to dissolve the sample before heating. Cooling the sample with ice will speed up the crystallization process.

Step-by-step explanation:

Temperature plays an important role in recrystallization. When dissolving a sample, it is crucial to use just enough hot solvent to dissolve the sample. The hot solvent should ideally keep the impurities either dissolved or not dissolve them at all. Cooling the sample with ice will speed up the crystallization process and promote the formation of large crystals. Furthermore, enough cold solvent should be added to dissolve the sample before heating it past its boiling point.

Let's say we have a compound that is soluble at high temperature and insoluble at low temperature. We dissolve the compound in a hot solvent and then cool it down. As the temperature drops, the compound will crystallize out of the solution, leaving the impurities still dissolved.

Answer 2

The correct answer is:

(1) It is important that the sample is dissolved in just enough hot solvent.

Step-by-step explanation:

The process of recrystallization is important to eliminate the impurities and to obtain better crystals of the solid. The solvent used to perform the recrystallization must have a high dissolution power of the substance to be recrystallized and a low dissolution power of the impurities. This is in order to eliminate most impurities. Furthermore, It is important that the sample is dissolved in just enough hot solvent because this should be easy to remove after the recrystallization and the crystal should form easily when the solution cools. Also, it is better to add the hot solvent to solubilize the crystals and keep the impurities insoluble, instead of adding the cold solvent and heating the solution. Additionally, the process of cooling the solution must be done slowly to obtain large and fewer crystals. A fast ice-cooling will form smaller crystals.