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 Potassium sodium tartrate tetrahydrate | |
| Names | |
|---|---|
| IUPAC name Sodium potassium L(+)-tartrate tetrahydrate | |
| Other names E337; Seignette's salt; Rochelle salt | |
| Identifiers | |
3D model (JSmol) | |
| ChemSpider |
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| ECHA InfoCard | 100.132.041 |
| EC Number |
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| E number | E337(antioxidants, ...) |
| UNII |
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| Properties | |
| KNaC4H4O6·4H2O | |
| Molar mass | 282.22 g/mol (tetrahydrate) |
| Appearance | large colorless monoclinic needles |
| Odor | odorless |
| Density | 1.79 g/cm3 |
| Melting point | 75 °C (167 °F; 348 K) |
| Boiling point | 220 °C (428 °F; 493 K) anhydrous at 130 °C; decomposes at 220 °C |
| 26 g / 100 mL (0 °C); 66 g / 100 mL (26 °C) | |
| Solubility in ethanol | insoluble |
| Structure | |
| orthorhombic | |
| Related compounds | |
Related compounds | Acid potassium tartrate;Aluminum tartrate;Ammonium tartrate;Calcium tartrate;Metatartaric acid;Potassium antimonyl tartrate;Potassium tartrate;Sodium ammonium tartrate;Sodium tartrate |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Potassium sodium tartrate tetrahydrate, also known asRochelle salt, is adouble salt oftartaric acid first prepared (in about 1675) by anapothecary,Élie Seignette [fr], ofLa Rochelle, France. Potassium sodiumtartrate andmonopotassium phosphate were the first materials discovered to exhibitpiezoelectricity.[3] This property led to its extensive use in crystalphonograph cartridges, microphones and earpieces during the post-World War II consumer electronics boom of the mid-20th century. Suchtransducers had an exceptionally high output with typical pick-up cartridge outputs as much as 2 volts or more. Rochelle salt isdeliquescent so any transducers based on the material deteriorated if stored in damp conditions.
It has been used medicinally as alaxative. It has also been used in the process ofsilvering mirrors. It is an ingredient ofFehling's solution (reagent for reducing sugars). It is used inelectroplating, inelectronics andpiezoelectricity, and as acombustion accelerator incigarette paper (similar to anoxidizer inpyrotechnics).[2]
In organic synthesis, it is used in aqueous workups to break upemulsions, particularly for reactions in which an aluminium-basedhydridereagent was used.[4] Sodium potassium tartrate is also important in the food industry.[5]
It is a common precipitant inprotein crystallography and is also an ingredient in theBiuret reagent which is used to measureprotein concentration. This ingredient maintainscupric ions in solution at an alkaline pH.
The starting material istartar with a minimum 68%tartaric acid content. This is first dissolved in water or in themother liquor of a previous batch. It is then basified with hot saturatedsodium hydroxide solution to pH 8, decolorized withactivated charcoal, and chemically purified before being filtered. The filtrate is evaporated to 42°Bé at 100 °C, and passed to granulators in which Seignette's salt crystallizes on slow cooling. The salt is separated from the mother liquor by centrifugation, accompanied by washing of the granules, and is dried in a rotary furnace and sieved before packaging. Commercially marketed grain sizes range from 2000 μm to < 250 μm (powder).[2]
Larger crystals of Rochelle salt have been grown under conditions of reduced gravity and convection on boardSkylab.[6]Rochelle salt crystals will begin to dehydrate when the relative humidity drops to about 30% and will begin to dissolve at relative humidities above 84%.[7]
In 1824, SirDavid Brewster demonstratedpiezoelectric effects using Rochelle salts,[8] which led to him naming the effectpyroelectricity.[9]
In 1919, Alexander McLean Nicolson worked with Rochelle salt, developing audio-related inventions like microphones and speakers at Bell Labs.[10]
Rochelle salt-based composites have gained renewed interest for their applications in impact energy absorption and smart sensing technologies.[11][12] Recent research has demonstrated the growth of Rochelle salt crystals within 3D-printedcuttlebone-inspired structures, resulting in multifunctional composites that combine mechanical robustness with piezoelectric properties. The chambered microstructure inspired by cuttlefish bone provides high stiffness and energy absorption capacity, making these composites suitable for protective equipment and structural health monitoring.[13]The developed composites exhibit remarkable mechanical performance, with enhanced fracture toughness and resistance to impact. Under cyclic loading, they maintain consistent piezoelectric output for up to 7000 cycles. Impact tests show voltage outputs peaking at approximately 8 V, and a piezoelectric coefficient (d33) around 30 pC/N.[13] These properties enable real-time sensing of impact forces, making the material suitable for use in wearable protective gear, such as smart armor for athletes and fall detection devices for the elderly.Sustainability and recyclability are notable advantages of this material. The Rochelle salt crystals can be dissolved and re-grown within the structure, allowing the composite to be repaired after damage. Recycled samples retain up to 95% of their original mechanical and piezoelectric performance.[13]Potential applications extend to sports safety equipment, aerospace structures, military armor, and biomedical monitoring devices, highlighting the versatility and functionality of Rochelle salt composites in modern material science.[13]
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