In a recrystallization from ethanol, cinnamic acid (pure mp 132-135 degree C) wa
ID: 476586 • Letter: I
Question
In a recrystallization from ethanol, cinnamic acid (pure mp 132-135 degree C) was melted on a melting point machine immediately after vacuum nitration, and found to have a melting point of 122-127 degree C. Why is the melting point not 132-135 degree C? Assume that there are no solid compounds present other than cinnamic acid, and explain in terms of what affects melting points, and how. Why should the filter be steam less when performing a hot gravity filtration? Construct a flow chart showing the purification of aspirin. Begin with aspirin, soluble impurities, and insoluble impurities. What is the purpose of adding water to the solution before cooling to get crystals? What does the term air drying mean when performing a vacuum filtration? What is the purpose of this? Heavy-walled vacuum tubing should be used when performing a vacuum filtration. Why is this? Show by means of a diagram. Would ammonium chloride dissolve better in water, or in ethanol? Why?Explanation / Answer
1. Since cinnamic acid recrystallized from ethanol is melted on a melting point machine immediately after vacuum filteration, the melting point will be lower than the melting point of pure cinnamic acid. This is because cinnamic acid is not dry. It is wet with ethanol. In the wet sample, the intermolecular forces present between ethanol and cinnamic acid are weaker than the intermolecular forces present between two cinnamic acid molecules. Weaker intermolecular forces leads to lower melting point.
2. Filter be stemless when performing a hot gravity filtration to prevent the solid from crystallization on cold stem.
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