Properties of common acids

① Hydrochloric acid (HCl) most chlorides are soluble in water, metals before hydrogen and most metal oxides and carbonates are soluble in hydrochloric acid, in addition, Cl - also has a certain reducibility, and can also form coordination ions with many metal ions to facilitate the dissolution of the sample. It is commonly used to dissolve hematite (Fe₂O₃), stibnite (Sb₂S₃), carbonate, permanganite (MnO₂) and other samples.
② Nitric acid (HNO) has a strong oxidation, almost all nitrates are soluble in water, in addition to platinum, gold and some rare metals, concentrated nitric acid can dissolve almost all metals and their alloys. Iron, aluminum, chromium, etc. are passivated by nitric acid, and non-oxidizing acids are added when dissolved, such as hydrochloric acid to remove the oxide film can be well dissolved. Almost all sulfides can also be dissolved by nitric acid, but hydrochloric acid should be added first, so that the sulfur is volatilized in the form of H₂S, so as not to pack the sample with elemental sulfur and affect decomposition. In addition, nitric acid is also very unstable, under heating or light conditions can be broken down into water, nitrogen dioxide and oxygen, and the higher the concentration of nitric acid, the easier it is to break down. Nitric acid also has strong oxidation, it can react with some metals, non-metals and reducing substances, as a result, the valence of nitrogen is reduced, into nitrogen dioxide or nitric oxide (concentrated nitric acid reacts with metals and non-metals to produce nitrogen dioxide, dilute nitric acid produces nitric oxide). In addition, nitric acid can also react with proteins to make them yellow.
③ Sulfuric acid (H₂SO₄) The sulfates of all metals dissolve in water except calcium, strontium, barium, and lead. Hot concentrated sulfuric acid has strong oxidation and dehydration, and is often used to decompose iron, cobalt, nickel and other metals and aluminum, beryllium, antimony, manganese, thorium, uranium, titanium and other metal alloys, as well as decompose organic matter in soil and other samples. Sulfuric acid has a high boiling point (338℃), and when the anion of low boiling point acids such as nitric acid, hydrochloric acid and hydrofluoric acid interferes with the determination, sulfuric acid is often added and evaporated to SO₃ to drive away.