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Potassium sodium tartrate

Potassium sodium tartrate
IUPAC name Potassium sodium tartrate
Other names E337
CAS number 304-59-6
EINECS number 206-156-8
Molecular formula KNaC4H4O6·4H2O
Molar mass 282.1 g/mol
Melting point

75 °C

Boiling point

220 °C

Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Potassium sodium tartrate is a double salt first prepared (in about 1675) by an apothecary, Pierre Seignette, of La Rochelle, France. As a result the salt was known as Seignette's salt or Rochelle salt.

It is a colorless to blue-white salt crystallizing in the orthorhombic system. Its molecular formula is KNaC4H4O6·4H2O. It is slightly soluble in alcohol but more completely soluble in water. It has a specific gravity of about 1.79, a melting point of approximately 75 °C, and has a saline, cooling taste. As a food additive, its E number is E337.

It has been used medicinally as a purgative but in more recent years its piezoelectric properties have been more important and it has found usage in phonograph pickups and other sensing devices. It has also been used in the process of silvering mirrors. It is an ingredient of Fehling's solution, formerly used in the determination of reducing sugars in solutions.

In organic synthesis, it is used in aqueous workups to break up emulsions, particularly for reactions in which an aluminum-based hydride reagent was used.

It is also an ingredient in the Biuret reagent which is used to measure protein concentration.


Rochelle salt (potassium sodium tartrate, NaKC4H4O6) can easily be prepared from potassium bitartrate (KHC4H4O6) and sodium carbonate (Na2CO3). First heat a potassium bitartrate solution. Add sodium carbonate to the still hot solution. Add sodium carbonate until no more reacts (Effervescence will occur). Filter the solution while hot and then heat to evaporate the water. After continued heating potassium sodium tartrate will precipitate.


    This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Potassium_sodium_tartrate". A list of authors is available in Wikipedia.
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