Detection of Carbon and Hydrogen

If a substance is already known (or strongly suspected) to be organic, there is technically no need to separately confirm the presence of carbon -- the carbon test in this section exists mainly as a way to establish, from scratch, WHETHER an unknown compound is organic at all. Hydrogen, by contrast, is worth confirming directly in almost every case, since with only a couple of exceptions (CCl4, CS2) every organic compound contains hydrogen alongside its carbon.

Both elements are confirmed together by a single test: the copper oxide test. The organic substance is ground together with roughly three times its own weight of dry copper oxide, and the mixture is packed into a hard-glass test tube fitted with a bent delivery tube whose far end dips into lime water held in a second test tube. Heating the mixture strongly drives the reaction: carbon present in the sample is oxidised by the copper oxide to carbon dioxide, and hydrogen present is oxidised to water. The carbon dioxide produced bubbles into the lime water and turns it milky -- a positive test for carbon. The water produced, being formed in the hot zone, condenses back out as small liquid droplets on the cooler walls of the test tube and inside its bulb; collecting this condensate on anhydrous coppe …