A student noticed that their aspirin had a melting range that was both lower and
ID: 1055781 • Letter: A
Question
A student noticed that their aspirin had a melting range that was both lower and wider than expected. In addition their aspirin had a noticeable strong odor of vinegar. What happened to the students sample to cause this? Again be sure to include an appropriate chemical equation as part of your answer. At the start of the experiment an aqueous base solution could have been used in the first extraction. In this case what compound would have been removed from the organic layer? Again be sure to include an appropriate chemical equation as part of your answer.Explanation / Answer
A pure organic compound usually melts over a range of two degrees or less. A sample is impure if it has a melting point range that is lower and wider than that the literature value. A substance (solid) containing soluble impurities usually melts at a lower temperature than the pure compound. It can also melt over a wide range of temperatures. This is called the melting point depression. So the lower and wider melting range of given aspirin sample indicates that it is an impure sample.
Salicylic acid and acetic anhydride in the presence of many hydrogen catalysts produce aspirin (acetyl salicylic acid) as a major product and acetic acid as a by-product. When aspirin becomes old, it gradually reacts with the moisture present in the air. Aspirin tablets that have high concentrations of acetic acid undergo a reverse process when exposed to wet surrounding or kept past their expiration date. Salicylic acid and acetic acid are released due to the breaking down of acetyl salicylic acid. This breakdown process produces the vinegar smell due to the resulting acetic acid.
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