Sodium Potassium Tartrate

Sodium Potassium Tartrate Tetrahydrate or Rochelle salt is a double salt of tartaric acid first prepared by an apothecary, Pierre Seignette, in about 1675.

Sodium Potassium Tartrate Crystals
Crystals of Rochelle salt (Source)
IUPAC NameSodium potassium-2,3-dihydroxy butane-1,4-dioate
Other NamesE337; Seignette’s salt; Rochelle salt
Chemical Formula\(C_4H_4O_6KNa . 4H_2O\)


Pierre Seignette of La Rochelle, France, in about 1675, first prepared Potassium sodium tartrate tetrahydrate. 

Piezoelectricity was first exhibited by Rochell’s salt and monopotassium phosphate. This property led to its extensive use in microphones and earpieces during post-World War II.

Structure of Sodium Potassium Tartrate

Structure of Potassium Sodium Tartrate
Structure (Source)

The sodium potassium tartrate is coordinated to ten oxygen atoms, four carbon atoms, one potassium, one sodium, and twelve hydrogen atoms.

This is a tetrahydrate, i.e. it has four water molecules (\(H_2O\)) attached to the salt.

Physical Properties

Molecular Weight (Tetrahydrous)282.10 g/mol
Molecular Weight (Anhydrous)210.16 g/mol
Density1.79 g / cm3
Melting Point75°C
Boiling Point220°C
AppearenceLarge colorless monoclinic needles
Water Solubility66g / 100ml (26°C)
Crystal StructureOrthorhombic

Chemical Properties

FlammabilityNon flammable or Combustible
ToxicityMildly toxic(For humans)
pH value7 – 8.5


First step is conversion of Sodium bicarbonate to Sodium carbonate.

\(2NaHCO_3   \rightarrow   Na_2CO_3 + CO_2 + H_2O\)

Potassium bitartrate reacts with sodium carbonate to generate the Rochelle salt.

\(KHC_4H_4O_6+ Na_2CO_3  \rightarrow  C_4H_4O_6KNa . 4H_2O\)


Fehling’s Solution Test 

The reaction between the copper(II) ions and aldehyde in Fehling’s solution is written as:

\(RCHO + 2 Cu^{2+} + 5 OH^{-}  \rightarrow  RCOO^{-} + Cu_2O + 3 H_2O\)

or with the tartrate included:

\(RCHO + 2 Cu(C_4H_4O_6)_2 ^{2-} + 5 OH^{-} \rightarrow  RCOO^{-} + Cu_2O + 4 C_4H_4O_6 ^{2-} + 3 H_2O\)


  1. Used as a Laboratory reagent
  2. One of the ingredients in the Biuret reagent, to measure the protein concentration.
  3. Used in the process of electroplating (Increases cathode efficiency.)
  4. It helps in maintaining alkaline pH.
  5. It is an ingredient in Fehling’s solution test and determination of uric acid.


What is formula for Sodium potassium tartrate(tetrahydrate)?

Chemical formula of sodium potassium tartarate(tetrahydrated) is \(C_4H_4O_6KNa . 4H_2O\)

What is Rochell’s Salt?

Rochell’s salt is another name for the chemical Sodium potassium tartarate(tetrahydrate), as it was first synthesized by Pierre Seignette of La Rochelle in 1675.

Is Sodium potassium tartarate/ Rochell’s salt soluble in alcohol?

Rochell’s Salt is partially soluble in alcohols.

Is sodium potassium tartrate hazardous?

If consumed it may cause irritation, mildly hazardous.

More on Inorganic Compounds

Mohr’s Salt (Fe(SO4)(NH4)2(SO4)(H2O)6)Ammonium Persulfate ((NH4)2S2O8)
Chlorine Trifluoride (ClF3)Sulfur Trioxide (SO3)
Sodium Sulfate (Na2SO4)Ammonium Bicarbonate ((NH4)HCO3)

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