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April 21, 2014

Homework Help: Mixed melting point

Posted by Sheryl on Sunday, October 1, 2006 at 8:16pm.

Question: A compound melting at 134 degrees C was suspected to be either aspirin (mp 135C) or urea (mp 133C) Explain how you could determine whether one of these two suspected compounds was identical to the unknown compound without using any form of spectroscopy.

This seems the same type of problem as my other most recent posting. It seems that the identity could be determined by a mixed melting point procedure if you had aspirin and urea available. A narrow melting point range would verify the substance and eliminate the other.

Sheryl


That's right. Another solution would be odor. Most aspirin smells faintly of acetic acid, expecially in moist air. It hydrolyzes. Urea, with most air and hydrolysis, smells like NH3. Urea is a base, aspirin is an acid so that will distinguish them also. But the mixed melting point is the correct answer here since that is what you are studying.

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