Question

The melting point of pure benzoic acid and pure naphthol are 122.5 *C and 123 *C respectively. You are given a pure sample that is known to be either pure benzoic acid or 2- naphthol. Describe a procedure you will use to determine the identity of the sample.

Answer 1

If you react the unknown sample with a weak aqueous solution of sodium bicarbonate, you will get one of two reactions:
a) formation of sodium benzoate if the sample had been benzoic acid
b) formation of an ether, if the sample had been 2-naphthol (likely in a separate layer on top).
Then, then a simple contuctivity test (ohmmeter) will either confirm ions (sodium benzoate solution), or not (ether from naphthol reaction).

Answer 2

Bob pursley, that seems like too much work.

FT-IR: Look for a peak at 1700, which would distinguish it from naphthol if it is Benzoic acid. Naphthol does not have a carbonyl group.

UV-VIS: Take the absorbance of the compound. If 2-naphthol, you should see a red shift in absorbance, somewhere around 250 or 260nm. Benzoic acid absorbs light at around 230 to 240nm.

Answer 3

UV-VIS: Take the absorbance of the compound. If 2-naphthol, you should see a red shift in absorbance, somewhere around 250 or 260nm. Benzoic acid absorbs light at around 230 to 240nm. 230nms to 240nm is on the high end.

Answer 4

I apologize. 2-naphthol should see a greater shift close to about 270 to 300 nm.