<unk>  is a strong inorganic acid that is used in many industrial processes such as refining metal. The application often determines the required product quality. Hydrogen chloride, not<unk> , is used more widely in industrial organic chemistry, e.g. for vinyl chloride and dichloroethane. Pickling of steel One of the most important applications of<unk>  is in the pickling of steel, to remove rust or iron oxide scale from iron or steel before subsequent processing, such as extrusion, rolling, galvanizing, and other techniques. Technical quality<unk>  at typically 18% concentration is the most commonly used pickling agent for the pickling of carbon steel grades. : Fe3O4 + Fe + 8<unk>  -> 4 FeCl2 + 4 H2O The spent acid has long been reused as iron(II) chloride (also known as ferrous chloride) solutions, but high heavy-metal levels in the pickling liquor have decreased this practice. The steel pickling industry has developed<unk>  regeneration processes, such as the spray roaster or the fluidized bed<unk>  regeneration process, which allow the recovery of<unk>  from spent pickling liquor. The most common regeneration process is the pyrohydrolysis process, applying the following formula: : 4 FeCl2 + 4 H2O + O2 -> 8<unk>  + 2 Fe2O3 By recuperation of the spent acid, a closed acid loop is established. The iron(III) oxide by-product of the regeneration process is valuable, used in a variety of secondary industries. Production of inorganic compounds Akin to its use for pickling,<unk>  is used to dissolve many metals, metal oxides and metal carbonates. The conversion are often depicted in simplified equations: : Zn + 2<unk>  → ZnCl2 + H2 : NiO + 2<unk>  → NiCl2 + H2O : CaCO3 + 2<unk>  → CaCl2 + CO2 + H2O These processes are used to produce metal chlorides for analysis or further production. pH control and neutralization<unk>  can be used to regulate the acidity (pH) of solutions. : OH^- +<unk>  -> H2O + Cl^- In industry demanding purity (food, pharmaceutical, drinking water), high-quality<unk>  is used to control the pH of process water streams. In less-demanding industry, technical quality<unk>  suffices for neutralizing waste streams and swimming pool pH control. Regeneration of ion exchangers High-quality<unk>  is used in the regeneration of ion exchange resins. Cation exchange is widely used to remove ions such as Na+ and Ca2+ from aqueous solutions, producing demineralized water. The acid is used to rinse the cations from the resins. Na+ is replaced with H+ and Ca2+ with 2 H+. Ion exchangers and demineralized water are used in all chemical industries, drinking water production, and many food industries. Laboratory use Of the six common strong mineral acids in chemistry,<unk>  is the monoprotic acid least likely to undergo an interfering oxidation-reduction reaction. It is one of the least hazardous strong acids to handle; despite its acidity, it contains the non-reactive and non-toxic chloride ion. Intermediate-strength<unk>  solutions are quite stable upon storage, maintaining their concentrations over time. These attributes, plus the fact that it is available as a pure reagent, make<unk>  an excellent acidifying reagent. It is also inexpensive.<unk>  is the preferred acid in titration for determining the amount of bases. Strong acid titrants give more precise results due to a more distinct endpoint. Azeotropic, or "constant-boiling",<unk>  (roughly 20.2%) can be used as a primary standard in quantitative analysis, although its exact concentration depends on the atmospheric pressure when it is prepared. Other<unk>  is used for a large number of small-scale applications, such as leather processing, household cleaning, and building construction. Oil production may be stimulated by injecting<unk>  into the rock formation of an oil well, dissolving a portion of the rock, and creating a large-pore structure. Oil well acidizing is a common process in the North Sea oil production industry.<unk>  has been used for dissolving calcium carbonate, e.g. such things as de-scaling kettles and for cleaning mortar off brickwork. When used on brickwork the reaction with the mortar only continues until the acid has all been converted, producing calcium chloride, carbon dioxide, and water: : CaCO3 + 2<unk>  -> CaCl2 + CO2 + H2O Many chemical reactions involving<unk>  are applied in the production of food, food ingredients, and food additives. Typical products include aspartame, fructose, citric acid, lysine, hydrolyzed vegetable protein as food enhancer, and in gelatin production. Food-grade (extra-pure)<unk>  can be applied when needed for the final product.
Hydrochloric acid
Dichloroacetic acid
Hydrofluoric acid
Denatured alcohol
Sodium hypochlorite
Potassium permanganate 
Gold salts
Chloroethane