Sodium sulfate

Disodium sulfate, disodium tetraoxosulfate, sodium sulfate or formerly sodium sulfate (Na₂SO4) is a colorless, crystalline substance with good solubility in water. water and poor solubility in most organic solvents with the exception of glycerin.

Sodium sulfate dissolves in water under cooling of the solution by entropic effect. Dehydrated salt releases energy (exothermic reaction) when hydrated and dissolved. When a saturated solution is cooled, supersaturation is often observed.

Chemical properties

Sodium sulfate is a typical ionic sulfate with electrostatic bonding. The existence of free sulfate ions in the solution is indicated by the easy formation of insoluble sulfates when these solutions are treated with Ba2+ or Pb2+ salts:

Na₂SO₄ + BaCl₂ → 2 NaCl + BaSO₄

Sodium sulfate is unreactive toward most oxidizing or reducing agents. At high temperatures, it can be converted to sodium sulfide by carbothermal reduction (also known as thermochemical sulfate reduction (TSR), high-temperature heating with charcoal, etc.):

Na₂SO₄ + 2 C → Na₂S + 2 CO₂

This reaction was used in the Leblanc process, a now-defunct industrial route for making sodium carbonate.

Sodium sulfate reacts with sulfuric acid to give the acid salt sodium bisulfate:

Na₂SO₄ + H₂SO₄ 2 2 NaHSO₄

Sodium sulfate shows a moderate tendency to form double salts. The only alums formed with common trivalent metals are NaAl(SO4)2 (unstable above 39 °C) and NaCr(SO4)2, in contrast to potassium sulfate and ammonium sulfate which form many stable alums. double salts are known with some other alkali metal sulfates, including the naturally occurring Na2SO4-3K2SO4 mineral aphytalite. The formation of glazerite by the reaction of sodium sulfate with potassium chloride has been used as the basis of a method for producing potassium sulfate, a fertilizer. Other double salts include 3Na₂SO₄ CaSO₄, 3Na₂SO₄MgSO₄ (vanthoffite) and NaF Na ₂SO₄.

Physical properties

Sodium sulfate has unusual solubility characteristics in water. Its solubility in water increases more than tenfold between 0 °C and 32.384 °C, where it reaches a maximum of 49.7 g/100 mL. At this point, the solubility curve changes slope and the solubility becomes almost independent of temperature. This temperature of 32.384 °C, which corresponds to the release of crystalline water and the melting of hydrated salt, serves as an accurate temperature reference for the calibration of a thermometer.

Applications

Anhydrous sodium sulfate has hygroscopic properties and is therefore used as a desiccant in the laboratory or chemical industry.

It is used in the manufacture of cellulose and as an additive in the manufacture of glass and plastic.

It is also added to powder detergents to improve their mechanical behavior, where it can represent a significant part of the total weight. It is used as a disinfectant, but it causes irritation after a short period of time.

It is useful in toxicology as an accelerator of intestinal transit (cathartic), together with the administration of activated charcoal, to reduce the intestinal absorption of ingested toxins. It is also used in foods as acidulants.

Summary

Currently, most of the sodium sulfate is obtained from glauberite mines and from the exploitation of salty lakes, the main producers being the provinces of Jiangsu and Sichuan in China, followed by Spain, where the largest deposits of sodium are located. glauberite from the world (in Cerezo de Río Tirón, Burgos). It is also obtained as a by-product in many industrial processes where sulfuric acid is neutralized with sodium bases.

History

Sodium sulfate is an essential part of the minerals found in many mineral waters and has astringent properties. Johann Rudolph Glauber (1604-1670), a Dutch/German chemist and apothecary, discovered it in 1625 in Austrian spring waters. He called it sal mirabilis (miracle salt), due to its medicinal properties: the crystals were used as a general purpose laxative, until more sophisticated alternatives emerged in the 1900s. He began with his manufacturing from salt (NaCl) and concentrated sulfuric acid between 1650 and 1660. This process is considered the beginning of the chemical industry. Because of this beginning, in German, apart from its systematic name, it is known as "Glaubersalz" and in English as "Glauber's salt" (Glauber's salt).

In the 18th century, Glauber's salt began to be used as a raw material for the industrial production of soda ash (sodium carbonate), by reaction with potash (potassium carbonate). The demand for sodium carbonate increased and the supply of sodium sulphate had to increase in line. Thus, in the 19th century, the large-scale Leblanc process, producing synthetic sodium sulfate as a key intermediate, it became the primary method of producing soda ash.

Analytics

Sodium is commonly determined by its emission of yellow light in the flame. Sulfate is usually determined by precipitating it as barium sulfate.