Distinguishing Test for Organic Compounds Given the following pairs of samples, how do I distinguish between them?

benzamide and ethanamide
ethanoyl chloride and ethanoic anhydride

My Approach:

We could easily convert the amides to amines by reducing them with $\ce{LiAlH4}$. Now, the question reduces to identifying the methyl group against the benzene group.

I am really lost here but my guess would be that we are looking for some characteristic reaction for anhydrides.
Since this sounds like an assignment, I am not going to give it all away. 

Does you have to use qualitative chemical tests? I don't even teach those anymore. They were supplanted by spectroscopic techniques in most professional labs decades ago.

IR spectroscopy would answer both questions quickly. 


Benzamide would have peaks characterizing an aromatic ring, for example:  $\ce{C}_{sp^2}\ce{-H}$ stretches around $3050-3100\ \mathrm{cm^{-1}}$. Ethanamide will not have these peaks, but will instead have $\ce{C}_{sp^3}\ce{-H}$ peaks $2800-3000\ \mathrm{cm^{-1}}$. There are other differences as well.
There are differences in the position (and sometimes number!) of carbonyl peaks between an anhydride and an acid halide. What are they?


So would mass spectrometry. Benzamide and ethanamide have different molar masses and different fragmentation patterns. Ethanoyl chloride... chlorine has two major isotopes. How can that help? 

NMR spectroscopy would also be useful. However, IR is cheap, fast, and easy.