Disodium dihydrogen pyrophosphate, Na2H2P2O7, is formed by heating sodium dihydrogen phosphate at about 200° C.:
2NaH2PO4 = Na2H2P2O7+H2O.
Above 300° C. it is converted into sodium metaphosphate.
In addition to the anhydrous salt, a tetrahydrate, and also a hexahydrate of density 1.848, are known. The aqueous solution has an acidic reaction, and reacts with sodium hydroxide to form the normal pyrophosphate. |