Does burning a substance and having it turn black mean that is contains carbon?
Yes. That black deposition is soot; pure carbon deposited as a by-product of incomplete combustion. When a combustible material burns in a limited oxygen supply, carbon monoxide and water are produced (as opposed to carbon dioxide and water when an excess of oxygen is present). Carbon monoxide, however, tends to decompose into carbon dioxide and pure carbon, which is deposited as soot: 2CO –> CO2 + C This soot can potentially burn as well if the oxygen supply and heat are both great enough. This is how a chimney fire starts; the hot gases from the fireplace heat up the soot on the chimney walls while simultaneously rising upwards, creating an updraft and a steady supply of oxygen. This will eventually ignite the soot on the inside of the chimney.
