Pyrophosphoric Acid

Acidity of pyrophosphoric acid The chain and ring structures of pyrophosphoric acid, tetrametaphosphoric acid or other polyphosphoric acids are formed by dehydration condensation of orthophosphoric acid, and are all condensed acids. Generally, the acidity of condensed acids is greater than that of monoacids. This is because the volume of condensed acid radical ions is large, and the negative charge density on their surfaces is much lower, so condensed acids are easy to dissociate protons. The greater the degree of condensation of similar oxygen-containing acids, the stronger the acidity. Uses: moisture retainer, quality improver, pH regulator, metal chelator. For toxicity, see industrial phosphoric acid. Chemical properties: colorless, transparent, crystalline solid or yellow syrupy liquid, highly hygroscopic. Solid pyrophosphoric acid is formed by the natural crystallization of a polyphosphoric acid mixture with a P2O5 content of 79.8%±0.2%. Soluble in ethanol and ether. When heated above the melting point, it decomposes into liquid acids containing orthophosphoric acid, pyrophosphoric acid, trimetaphosphoric acid, polymetaphosphoric acid, etc. Crystalline pyrophosphoric acid does not decompose much in ice water, but decomposes at high temperatures, and the amount of orthophosphoric acid increases. The general solid crystal is type I pyrophosphate (melting point 54.3). Type I crystals are heated at about 50 for several hours in a closed tube and then become type II (melting point 71.5). This product is stable at room temperature. Uses: used as catalyst, concealing agent, metal refining, stabilizer for organic peroxides. It is also used to adjust the Ph value of the electroplating solution in the copper electroplating process.