Sodium phosphate, tribasic

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White, crystalline, hygroscopic powder. Tribasic sodium phosphate, or TSP, is used as a Water softener, Sequestrant, Buffer, Emulsifier, and Flame retardant. It removes dissolves hard water deposits including boiler scale. TSP is used in detergents, metal cleaners, paint removers, paper manufacturing, and leather tanning. It is also used in developing baths for color photographs.

Synonyms and Related Terms

TSP; trisodium phosphate; trisodium orthophosphate; tertiary sodium phosphate; sodium hypophosphate; Oakite; phosphate cleaner


  • Nonflammable.
  • Toxic by ingestion.
  • Skin contact causes irritation.
  • ThermoFisher: SDS

Other Properties

Soluble in water, ethanol. pH = 11.8 - 12.0 for a 1% solution.

Composition Na3PO4 - 12H2O
CAS 7601-54-9
Melting Point 75 C (dec)
Density 1.62 g/ml
Molecular Weight mol. wt. = 380.12
Refractive Index 1.4653, 1.4738, 1.4804

Resources and Citations

  • G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 824
  • Richard S. Lewis, Hawley's Condensed Chemical Dictionary, Van Nostrand Reinhold, New York, 10th ed., 1993
  • Michael McCann, Artist Beware, Watson-Guptill Publications, New York City, 1979
  • Thomas C. Jester (ed.), Twentieth-Century Building Materials, McGraw-Hill Companies, Washington DC, 1995
  • The Merck Index, Martha Windholz (ed.), Merck Research Labs, Rahway NJ, 10th edition, 1983 Comment: entry 8008
  • Photographic chemicals:
  • Van Nostrand's Scientific Encyclopedia, Douglas M. Considine (ed.), Van Nostrand Reinhold, New York, 1976
  • Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
  • The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
  • CRC Handbook of Chemistry and Physics, Robert Weast (ed.), CRC Press, Boca Raton, Florida, v. 61, 1980 Comment: ref. index = 1.4653, 1.4738, 1.4804

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