Phosphoric Acid

About This Product

Phosphoric acid, orthophosphoric acid, has the formula H3PO4 and CAS number 7664-38-2. It is supplied as a clear, colourless, syrupy liquid, most commonly at 75 or 85 percent concentration, and is manufactured either by the wet process, digesting phosphate rock with sulphuric acid, or by the thermal process, which gives the higher purity needed for food and electronic grades. It is triprotic, meaning it can give up three protons in sequence with pKa values of roughly 2.1, 7.2 and 12.3, and that stepwise dissociation is the basis of the entire phosphate family. Neutralising the first proton gives dihydrogen phosphates such as MSP and MKP, the second gives hydrogen phosphates such as DSP and DKP, and the third gives the fully neutralised trisodium and tricalcium salts. Each has a different pH and a different function, but all are made by stopping the same neutralisation at a different point. Used directly, the acid attacks iron oxide and converts it to an adherent iron phosphate layer, which is the mechanism behind both rust conversion and the phosphating pretreatment applied to steel before painting. It is used in metal treatment and phosphating, rust conversion, descaling, fertiliser and phosphate salt manufacture, water treatment and electropolishing. Bio Green Chem supplies technical, food and electronic grades to specification on assay, chlorides, sulphates, iron, arsenic, fluoride and heavy metals.