What is Rochelle salt
Rochelle salt or Potassium sodium tartrate tetrahydrate is an odourless, colourless to white crystalline solid with a salty taste. It is the double salt of tartaric acid. It is soluble in water but insoluble in alcohols. Potassium Sodium Tartrate is prepared from potassium bitartrate and sodium carbonate. Commercially it is produced as a by-product of the wine industry.
Properties and specification of Rochelle salt
- Synonyms: Potassium Sodium Tartrate; E337; Seignette’s salt; Rochelle salt; Potassium sodium tartrate tetrahydrate; Potassium sodium 2,3-dihydroxysuccinate; L(+)-Tartaric acid potassium Sodium salt; butanedioic acid, 2,3-dihydroxy-, potassium sodium salt
- CAS number: 304–59–6
- EINECS: 206–156–8
- Purity: >99%
- Appearance: colourless / white crystalline solid
- Molecular weight: 282.1
- pH: 7–8.5
- Density: 1.79
- Specific gravity: 2.75 g/cm3
- Solubility in water: soluble 630g/L @20C
- Melting point: 75C
- Boiling point: 220C
- Refractive index: 1.59
- Oil Absorption: 37g/100g
The chemical composition of Potassium sodium tartrate tetrahydrate consists of Water 24.53%, Potassium 13.85%, Sodium 8.15% and Tartaric acid 53.17%. When heated it melts at 70–80C; at 100C it loses 3 water molecules and eventually becomes anhydrous at 130–140C; at 220C it begins to decompose. Potassium Sodium Tartrate has the linear formula KOCOCH(OH)CH(OH)COONa.4H2O
How to make Rochelle salt crystals
The salt is prepared by adding 0.5M sodium carbonate to a hot solution of 1M potassium bitartrate (cream of Tartar). The solution is mixed thoroughly and then filtered while hot. This solution is then dried to precipitate solid potassium sodium tartrate, as small crystals.
Uses for Rochelle salt
As additive in food industry ( E337 ) where it acts as sequestrant, emulsifier, stabilizer, buffer and antioxidant in cheese products, margarine, jellies, jams, minced meat, and sausage casings.
In pharmacology it is used as saline cathartics (usual adult dose: 5–10g). potassium bitartrate is administered rectally as a suppository with sodium bicarbonate to produce carbon dioxide, which promotes defecation by distending the rectal ampulla; administered for relief of constipation, and evacuation of the colon before surgical or diagnostic procedures or childbirth. It is not to be used on persons with heart problems or those on low sodium diets.
Potassium Sodium Tartrate is also used for the removal of toxic materials in some cases of poisoning.
Other applications include the preparation of piezoelectric crystals used in electrical appliances; as a laxative; in the manufacture of mirrors; in the plating industry; as a laboratory reagent; in the preparation of Fehlings solution for the detection of aldehydes; and for delaying the quick-setting of gypsum .
Health & Safety
This substance is not classified as dangerous according to Directive 67/548/EEC.
For full details see MSDS for Rochelle salt
Other Tartrate salts: