Why is salt peter added to blackpowder, what does it do?
Saltpeter (either potassium nitrate or sodium nitrate, depending upon who’s calling what what) is an oxidizer. This means that it is capable of oxidizing other substances under some conditions. The reason that nitrates are such good oxidizer is that nitrate group (the -NO3 ligand) is very good at splitting off its oxygens, which then may be used to oxidize other compounds. Saltpeter (as potassium nitrate) is added to charcoal in a ratio of about 15:3:2; it does not have a lot of oxygen to “go around,” facilitating the reaction. See also reference 1 and 2.
