Sodium Potassium Tartrate

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This article deals with Sodium potassium tartrate, also known as Rochelle salt, which is a double salt of tartaric acid. It was first prepared in the year 1672 by an apothecary, Pierre Seignette, of La Rochelle, France. Rochelle salt is a white crystalline powder and a slightly bitter taste. It has a pH range of 6.5 – 8.5. It is obtained by the reaction of Sodium Hydroxide on the crude Cream of Tartar which is a by-product of the Wine Industry. It is almost insoluble in alcohol and ether.

Properties of Sodium Potassium Tartrate

Sodium potassium tartrate formula / Rochelle salt

C₄H₄O₆KNa . 4H₂O

Molar Mass

282.1 g/mol


1.79 g/cm³

Melting Point


Boiling Point


Sodium Potassium Tartrate Uses

  • Used in Laboratory reagent, one of the ingredients in Biuret reagent to measure the concentration of protein.

  • It is used in the electroplating process (Increases cathode efficiency.), in electronics, and piezoelectricity.

  • It is used in cigarette paper. (Delays the consumption of cigarette paper.)

  • It helps in maintaining alkaline pH.

  • It is used in the silvering of mirrors. (Act as a reducing agent)

  • It is also used in the Pharmaceutical Industry.

  • It is used in gas purification.

  • It is an ingredient in Fehling's solution test (reagent used in reducing sugars) and determination of uric acid.

Sodium Potassium Tartrate Structure

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Sodium Potassium tartrate/ Rochelle salt contains ten oxygen atoms, twelve hydrogen atoms, four carbon atoms, one potassium atom, and one sodium atom. 


Reactions Involved in the Preparation of Rochelle Salt/Potassium Tartrate

The first step involves the Conversion of sodium bicarbonate to sodium carbonate

2NaHCO₃   →   Na₂CO₃ + CO₂ + H₂O

Potassium bitartrate reacts with sodium carbonate to generate Sodium Potassium Tartrate / Rochelle salt:

KHC₄H₄O₆ + Na₂CO₃  →  C₄H₄O₆KNa . 4H₂O 

Did you know?

Rochelle Salt must be stored in a dry place with airtight packing and, away from humidity and in normal temperature conditions and its IUPAC name is sodium potassium-2,3-dihydroxy butane-1,4-dioate.

FAQ (Frequently Asked Questions)

Question: Write Some Applications of Rochelle Salt.

Answer: It is used in Food Industries, Wall Plaster, Pharmaceutical industry, Treatment of metals, Electroplating (Increased anodic solubility, Greater surface uniformity, Increased cathode efficiency.), Silvering of mirrors, Piezoelectrical effect, etc.

Question: Rochelle Salt is Soluble in Alcohol?

Answer: Sodium Potassium Tartrate/Rochelle salt is partially soluble in alcohol.

Question: What is the Function of Rochelle Salt in Fehling Solution?

Answer: Fehling’s solution is used to identify the presence of aldehydes or groups that contain any aldehyde functional group -CHO and also used to differentiate a ketone group and water-soluble carbohydrates.

This solution is always prepared freshly in the laboratory. It is made initially in two separate solutions, known as Fehling's A and Fehling's B. Fehling's A is a blue aqueous solution of copper(II) sulphate pentahydrate crystals, and Fehling's B is a clear solution of aqueous potassium sodium tartrate (also known as Rochelle salt) mixed with a strong alkali (commonly known as sodium hydroxide).

Fehlings Solution A and B are kept separate because if we combine the two, the Copper Tartarate complex formed will be quickly degraded, and will not be effective in detecting “reducing sugars” (sugars containing aldehyde groups).