Phosphoric acid is used in the manufacture of superphosphate fertilisers, livestock feeds, phosphate salts, polyphosphates, soaps, waxes, polishes and detergents. Phosphoric acid is used as a soil stabiliser, in the manufacture of fire control agents, opal glasses, electric lights, in cotton dyeing, tile cleaning, ceramic binding, dental cement, water treatment, electro-polishing, operating lithography, photoengraving operations, process engraving, as a petrol additive and in coagulating rubber latex. It is used in metal rust proofing before painting, in the polishing of metals, in pickling and in hot stripping for aluminium and zinc substrates. Phosphoric acid is used as an acid catalyst in making ethylene and purifying hydrogen peroxide, in the manufacture of chemicals (ethylbenzene, propylene, cumene), as a bonding agent for refractory bricks, in extracting penicillin and as an analytical agent. It is used as an anti-oxidant in food, as a flavour additive for sharp taste in food (jellies, preserves) and soft drinks (e.g. Coca-Cola), as a tang (Food Additive 338) and for the manufacture of yeasts and gelatine. It is used to manufacture the phosphoric acid electrolyte fuel cell system and it has been used to treat lead poisoning.
Substance name: Phosphoric acid
CASR number: 7664-38-2
Molecular formula: H3O4P (or PO(OH)3)
Synonyms: Orthophosphoric acid, white phosphoric acid, Sonac
Pure phosphoric acid is a non-combustible, colourless, odourless and hygroscopic crystal. Commercial phosphoric acid comes as a viscous solution in water which contains 75-85% phosphoric acid. The liquid can solidify at lower temperatures.
Melting Point: 42°C (pure)
Boiling Point: 260°C (pure)
Specific Gravity: 1.88 (pure)
Vapour Density: 3.4 (pure)
Phosphoric acid can be made using either of two different methods. One method is by direct reaction of ground phosphate rock with sulfuric acid which also produces a lot of gypsum (calcium sulfate) as waste by-product. The second method is by burning elemental phosphorous and subsequent hydration of the phosphorous oxide. Phosphoric acid is a corrosive acid that can form three different classes of salts, namely primary phosphates, dibasic phosphates and tribasic phosphates. Phosphoric acid is soluble in water. It is incompatible with strong caustics and it is corrosive to ferrous metals and alloys. It readily reacts with metals to form flammable hydrogen gas. Phosphoric acid decomposes under formation of toxic fumes on contact with alcohols, aldehydes, cyanides, ketones, phenols, esters, sulfides, mercaptans and halogenated organic compounds. Phosphoric acid forms toxic phosphorous oxide fumes on combustion.
The National Pollutant Inventory (NPI) holds data for all sources of phosphoric acid in Australia.
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