Potassium sodium tartrate

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Potassium sodium tartrate
Skeletal formula of potassium sodium tartrate
Space-filling model of part of the crystal structure of potassium sodium tartrate
IUPAC name
Potassium sodium tartrate
Other names
304-59-6 YesY
ChemSpider 8031536 YesY
EC number 206-156-8
Jmol-3D images Image
PubChem 9855836
Molar mass 282.1 g/mol
Melting point 75 °C (167 °F; 348 K)
Boiling point 220 °C (428 °F; 493 K)
630 g/L (20 °C)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox 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. Rochelle salt is not to be confused with rock salt, which is simply the mineral form of sodium chloride. Potassium sodium tartrate and monopotassium phosphate were the first materials discovered to exhibit piezoelectricity.[2] This property led to its extensive use in "crystal" gramophone (phono) pick-ups, microphones and earpieces during the post-War consumer electronics boom of the mid-20th Century. Such transducers had an exceptionally high output with typical pick-up cartridge outputs as much as 2 volts or more. Rochelle salt is deliquescent so any transducers based on the material deteriorated if stored in damp conditions.

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 laxative. It has also been used in the process of silvering mirrors. It is an ingredient of Fehling's solution and Nylander's test, 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 aluminium-based hydride reagent was used.[3] Sodium Potassium tartrate is also important in Food Industry. [4]

It is a common precipitant in protein crystallography and is also an ingredient in the Biuret reagent which is used to measure protein concentration. This ingredient maintains cupric ions in solution at an alkaline pH.


Large Rochelle salt crystal grown aboard Skylab

Sodium Potassium tartrate, (NaKC4H4O6) may be prepared by adding 0.5 mole sodium carbonate(Na2CO3) to heated solution containing 1 mole potassium bitartrate(KHC4H4O6). (1M KHC4H4O6 : 0.5M Na2CO3). The solution is filtered while hot. This solution is then dried to precipitate solid potassium sodium tartrate, as small crystallites.

Larger crystals of Rochelle salt have been grown under conditions of reduced gravity and convection on board Skylab .[5]


  1. ^ http://www.chemblink.com/products/6381-59-5.htm
  2. ^ Newnham, R.E.; Cross, L. Eric (November 2005). "Ferroelectricity: The Foundation of a Field from Form to Function". MRS Bulletin 30: pp. 845–846. doi:10.1557/mrs2005.272. 
  3. ^ Fieser, L. F.; Fieser, M., Reagents for Organic Synthesis; Vol.1; Wiley: New York; 1967, p. 983
  4. ^ "Rochelle Salt applications". 
  5. ^ "SP-401 Skylab, Classroom in Space". NASA. Retrieved 2009-06-06.