Sodium dithionite (aka Sodium hydrosulfite) is a toxic, white crystalline powder with a weak sulforous odor. It is stable under most conditions, although it will decompose in hot water and in acid solutions. It can be produced by the following reaction:

$2NaHSO\_3\; +\; Zn\; \backslash rightarrow\; Na\_2S\_2O\_4\; +\; Zn(OH)\_2$

This compound is a water soluble salt, and can be used as a reducing agent in aqueous solutions. It is used as such in some industrial dying processes, where an otherwise water-insoluble dye can be reduced into a water-soluble alkali metal salt. The reduction properties of sodium dithionite also eliminate excess dye, residual oxide, and unintended pigments, thereby improving overall colour quality. It can also be used as a bleach, in, for instance, paper pulp, cotton, wool, and kaolin clay.

This chemical can also be used for water treatment, gas purification, cleaning, and stripping. It can also be used in industrial processes as a sulfonating agent or a sodium ion source. In addition to the textile industry, this compound is used in industries concerned with leather, foods, polymers, photography, and many others.

Sodium dithionite is often used in physiology experiments as a means of lowering solution's redox potential (E^o' ~ -420 mV at pH 7). Potassium ferricyanide is usually used as an oxidizing chemical in such experiments (E^o' ~ 436 mV at pH 7). Additionally, Na-dithionite is often used in soil chemistry experiments to determine the amount of Fe that is not incorporated in primary silicate minerals. Hence, Fe extracted by Na-dithionite is also referred to as "free Fe". The strong affinity of the dithionite ion for bi- and trivalent metal cations allows it to enhance the solubility of Fe, and therefore dithionite is a chelating agent.

External links

Sodium compounds | Bleaches

Dithionit sodný | Natriumdithionit