of the Si–F bond in the side product. Protonation using simply fluoroantimonic acid, however, has met with failure, as pure sulfuric acid undergoes self-ionization to give ions: which prevents the conversion of to by the HF/ system. Reactions with metals Even dilute sulfuric acid reacts with many metals via a single displacement reaction, like other typical acids, producing hydrogen gas and salts (the metal sulfate). It attacks reactive metals (metals at positions above copper in the reactivity series) such as iron, aluminium, zinc, manganese, magnesium, and nickel. Concentrated sulfuric acid can serve as an oxidizing agent, releasing sulfur dioxide: Lead and tungsten, however, are resistant to sulfuric acid. Reactions with carbon and sulfur Hot concentrated sulfuric acid oxidizes carbon (as bituminous coal) and sulfur: Reaction with sodium chloride It reacts with sodium chloride, and gives hydrogen chloride gas and sodium bisulfate: Electrophilic aromatic substitution Benzene undergoes electrophilic aromatic substitution with sulfuric acid to give the corresponding sulfonic acids: Occurrence Pure sulfuric acid is not encountered naturally on Earth in anhydrous form, due to its great affinity for water. Dilute sulfuric acid is a constituent of acid rain, which is formed by atmospheric oxidation of sulfur dioxide in the presence of water – i.e. oxidation of sulfurous acid. When sulfur-containing fuels such as coal or oil are burned, sulfur dioxide is the main byproduct (besides the chief products carbon oxides and water). Sulfuric acid is formed naturally by the oxidation of sulfide minerals, such as iron sulfide. The resulting water can be highly acidic and is called acid mine drainage (AMD) or acid rock drainage (ARD). This acidic water is capable of dissolving metals present in sulfide ores, which results in brightly colored, toxic solutions. The oxidation of pyrite (iron sulfide) by molecular oxygen produces iron(II), or : The can be further oxidized to : The produced can be precipitated as the hydroxide or hydrous iron oxide: The iron(III) ion ("ferric iron") can also oxidize pyrite: When iron(III) oxidation of pyrite occurs, the process can become rapid. pH values below zero have been measured in ARD produced by this process. ARD can also produce sulfuric acid at a slower rate, so that the acid neutralizing capacity (ANC) of the aquifer can neutralize the produced acid. In such cases, the total dissolved solids (TDS) concentration of the water can be increased from the dissolution of minerals from the acid-neutralization reaction with the