Recrystallisation is a very important technique in synthetic chemistry. A critical step is in selecting a solvent system where the impurities are very soluble but the product is only partly soluble. The mixture for purification is heated to dissolve all of the product in a super saturated solution. On cooling the product starts to crystallise out of solution as it's solubility is poor at room temperature. If you have chosen your solvent correctly your impurity will stay in solution. Watch this short video and answer the following questions about recrystallisation. Note: this is an example recrystallisation and not actually an aspirin recrystallisation. Why do we allow our recrystallisation to cool slowly? Please select the most accurate answer.单项选择题

题目图片
A

a. To allow crystals to form quickly so there is less chance impurities get trapped.

B

b. To allow crystals to form slowly so there is less chance impurities get trapped.

C

c. To allow the largest mass of crystals to form.

D

d. To allow large crystals to form.

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