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July 1, 2015

Homework Help: Chemistry

Posted by Paul on Thursday, April 2, 2009 at 4:29pm.

Aspirin can be prepared by the reaction of salicylic acid with an excess of acetic anhydride, using phosphoric acid as a catalyst. Once the aspirin is formed, it is precipitated from the reaction mixture by adding water and filtering. The solid aspirin obtained in this way is contaminated with acetic acid. To purify it, it will be recrystallized from an ethanol-water mixture. Recrystallization is a commonly-used method for the purification of solids. In this case it is done by dissolving the impure aspirin in a hot ethanol-water mixture; purified aspirin will recrystallize upon cooling the solution.

If the recrystallization step was skipped, would this result in an increase or decrease of the apparent percent yield or have no effect?

I feel that it would result in an increase in the apparent percent yield because the actual yield would be larger than what it would have been had the recrystallization been carried out.

Is this reasoning correct?

Also, from the above description of the experiment, what does "The solid aspirin obtained in this way is contaminated with acetic acid" mean in simple terms?

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