Formula (NaPO3)6 Density 2.48 g/cm³ Boiling point 1,500 °C | Molar mass 611.77 g/mol Melting point 628 °C Appearance White crystals | |
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Related compounds | ||
Sodium hexametaphosphate
Sodium hexametaphosphate (SHMP) is a hexamer of composition (NaPO3)6. Sodium hexametaphosphate of commerce is typically a mixture of polymeric metaphosphates, of which the hexamer is one, and is usually the compound referred to by this name. It is more correctly termed sodium polymetaphosphate.
Contents
Sodium hexametaphosphate
Uses
SHMP is used as a sequestrant and has applications within a wide variety of industries, including as a food additive in which it is used under the E number E452i. Sodium carbonate is sometimes added to SHMP to raise the pH to 8.0–8.6, which produces a number of SHMP products used for water softening and detergents.
A significant use for sodium hexametaphosphate is as a deflocculant in the production of clay-based ceramic particles. It is also used as a dispersing agent to break down clay and other soil types for soil texture assessment.
It is used as an active ingredient in toothpastes as an anti-staining and tartar prevention ingredient.
Food additive
Artificial maple syrup, canned milk, cheese powders and dips, imitation cheese, whipped topping, packaged egg whites, roast beef, fish fillets, fruit jelly, frozen desserts, salad dressing, herring, breakfast cereal, ice cream, beer, and bottled beverages, among other foods, can contain sodium hexametaphosphate.
Preparation
SHMP is prepared by heating monosodium orthophosphate to generate sodium acid pyrophosphate:
2 NaH2PO4 → Na2H2P2O7 + H2OSubsequently, the pyrophosphate is heated to give the corresponding sodium hexametaphosphate:
3 Na2H2P2O7 → (NaPO3)6 + 3 H2Ofollowed by rapid cooling.
Reactions
SHMP hydrolyzes in aqueous solution, particularly under acidic conditions, to sodium trimetaphosphate and sodium orthophosphate.