if ferric chloride was added to an unknown which happened to be benzophenone to identify if it has the phenol functional grp...will the sol'n turn purple (it contains the phenol) or yellow(does not contain phenol)?
Benzophenone is a ketone and ketones don't give a ferric chloride test UNLESS they form the enol tautomer. Does it form the enol? I did not find anything on the Internet to tell me if benzophenone will give a positive ferric chloride test or not. Couple that with the fact that not ALL enols/phenols give a positive ferric chloride test and that leaves me with the suggestion that you try this in the lab. Sorry I can't be of more help.
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When ferric chloride is added to an unknown compound to test for the presence of a phenol functional group, a positive result is indicated by the formation of a purple color. In the case of benzophenone, which is a ketone and does not contain a phenol functional group, the solution should not turn purple. However, as you mentioned, ketones can potentially form enol tautomers that can react with ferric chloride, but the formation of an enol tautomer in benzophenone is not favored. As a result, it is more likely for the solution to turn yellow, indicating a negative ferric chloride test (i.e., no phenol group is present). Of course, running the test in the lab is the best way to confirm this prediction.
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