IR Spectroscopy allows us to identify what type of molecule a sample is as different types of bonds absorb different types of frequency. Peaks of an IR spectroscopy graph can be matched with wavenumbers in a data sheet to identify what type of bond is present.
Tollens and Fehling's reagent allow us to test for the aldehyde functional group. Sodium carbonate allows us to test for carboxylic acids. Acidifed potassium dichromate tests for primary and secondary alcohols.