What Is Sodium Tartrate?
Sodium potassium tartrate is a compound salt consisting of sodium and potassium salts in tartaric acid.
It is also known as Rochelle salt or Seignette salt. In its normal state, it exists as colorless or bluish-white crystals. It is soluble in water but insoluble in alcohol.
Uses of Sodium Tartrate
Sodium tartrate is a compound with a strong piezoelectric effect and high dielectric constant, so it can be used as an oscillator or piezoelectric element, or in microphones and handsets. Industrially, sodium potassium tartrate is synthesized by reacting sodium hydrogen tartrate with an aqueous solution of sodium carbonate.
It is also the main ingredient in other Fehling’s solutions and is registered as a food additive in the EU. It is also used in the pharmaceutical and food industries. Furthermore, because of its mild reducing action, it is used as a reducing agent in the electroless plating of silver, and was used to make mirrors from plate glass in the past.
Properties of Sodium Tartrate
Sodium tartrate has a molar mass of 282.1, a melting point of 75°C, and a boiling point of 220°C. Sodium tartrate crystals dissolve at a relative humidity above about 84% and dehydrate at a relative humidity below about 30%.
Sodium potassium tartrate is a salt of the divalent carboxylic acid tartrate with sodium and potassium. It usually contains four molecules of crystalline water and has the chemical formula KNaC4H4O6-4H2O.
Other Information on Sodium Potassium Tartrate
1. Formation of Sodium Potassium Tartrate
Sodium potassium tartrate can be prepared by adding 0.5 moles of sodium carbonate to a heated solution containing 1 mole of potassium hydrogen tartrate. The solution is filtered while hot and the filtrate is dried, resulting in the precipitation of solid Sodium Tartrate as crystallite.
Experiments have been conducted at Skylab under microgravity and convection conditions to study the growth of Rochelle salt into large crystals.
2. Chelating Action of Sodium Tartrate
Sodium tartrate has high solubility in water, and in water it ionizes to form tartrate ions with chelating properties. Therefore, sodium tartrate can be widely used as a weakly basic chelating agent.
In organic synthesis, sodium tartrate is used as a post-treatment for reactions using aluminum hydride reagents, such as lithium aluminum hydride (LAH) and diisobutyl aluminum hydride (DIBAL-H). Sodium tartrate can prevent the formation of emulsions and precipitations during aliquot handling due to its chelating action.
It is also used industrially as a component of plating solutions and as a reagent in chemical analyses such as Fehling’s reaction, Biuret test, Nessler reaction, and determination of cadmium.
3. Piezoelectric Effect of Sodium Tartrate
Single crystals of sodium tartrate will exhibit a high dielectric constant of about 4,000 as a ferroelectric material. On the other hand, it also has a lower Curie temperature limit and does not exhibit ferroelectricity only in the temperature range of 255-297K.
In the past, piezoelectric elements were widely used for crystal microphones and crystal earphones, taking advantage of this feature. Today, however, other materials such as barium titanate (BT) and potassium dihydrogen phosphate (KDP) have been discovered as piezoelectric elements, and the use of moisture-sensitive sodium tartrate is almost non-existent.