Sodium Thiosulphate is a colorless, odorless salt that is inorganic in nature. It is a crystalline compound with five molecules of water in it. It is also referred to as disodium thiosulphate with the chemical formula of Na2S2O3. When it is decomposed by the application of heat it emits highly toxic fumes of sulfur oxides. It is often found in toxic wastes of dye industries. It is basically an ionic compound formed from two sodium cations with one thiosulfate anion where one sulfur atom is bonded to three oxygen atoms and one another sulfur atom. The oxygen atoms are bonded to the sulphur atom by double bonds and the other sulfur atm by a single bond. This compound has many applications in day-to-day use and its highly soluble nature serves as the basis of its importance. It becomes amorphous when the five water molecules are lost.
Physical Properties of Sodium Thiosulphate
Appearance: Thiosulphate is a bright crystalline crystal, which is odorless and highly soluble in water.
Chemical formula: The chemical formula of thiosulphate is represented as Na2S2O3.
Density: The solid has a density of about 1.667 g/ ml.
Melting Point: The substance melts at a temperature of 48.3 degrees Celsius.
The compound mostly exists in its hydrated form, written as Na2S2O3.xH2O. Naturally, this white crystalline compound is found in its pentahydrate form represented as Na2S2O3.5H2O.
Chemical Properties of Sodium Thiosulphate
Na2S2O3 + H2O → Na+ + S2O3-
Stability: From the structure of thiosulfuric acid, it’s clear that this inorganic solid is highly stable. It is highly compatible with some of the strong acids and strong oxidizing agents. However, when reacted with dilute acids, the substance gets decomposed to produce sulfur.
Reaction Upon Heat: Though thiosulphate is a stable substance under normal conditions. However, if some heat is provided, then it decomposes to give sodium polysulfide and sodium sulfate.
4Na2S2O3 → 3Na2SO4 + Na2S5
Na2S2O3 + 2HCl (Dilute Hydrochloric Acid) → 2 NaCl + S + SO2 + H2O
Structure of Sodium Thiosulphate
Having a chemical formula as Na2S2O3, thiosulphate is an ionic compound that consists of two cations of a sodium atom, that is, Na+ and a negatively charged anion of thiosulfate, that is, S2O3-. From the thiosulphate structure, it’s clear that the central atom (S) forms one bond with sulfur and other bonds to three oxygen atoms. The central atom forms two bonds with each atom, single and double possessing resonance character.
The above diagram represents the structure of sodium thiosulfate. In this, the central atom (S) forms one single and one double bond with three oxygen atoms and one sulfur atom.
In the structure of thiosulfuric acid, the thiosulfate anion is obtained by the replacement of one of the oxygen atoms by the use of sulfur (S) atom in the sulfate anion. Thus, it forms a tetrahedral structure.
Preparation of Sodium Thiosulphate
Sodium Thiosulphate is usually prepared by heating sulfur along with aqueous sodium hydroxide solution or by using aqueous sodium sulfite solution.
6NaOH + 4S → Na2S2O3 + 2Na2S + 3H2O
The structure of thiosulfuric acid shows that the solid also occurs in a monoclinic crystalline structure. Thiosulphate is not a toxic material, and thus commonly possesses wide medical applications. However, when decomposed, this chemical compound produces toxic sulfur oxide fumes. The fumes formed can cause irritation to skin, eyes, and even mucous membranes.
The above diagram shows sodium thiosulphate contains two types of ions. Two cations of sodium and an anion of thiosulphate.
Applications of Thiosulphate in Real-Life
Due to stable thiosulphate structure, the substance is widely used in different fields such as gold extraction, photography, medicine, and other areas.
Photography: This chemical substance is often used as a fixing agent in photography. It helps in dissolving the silver salts from the negatives.
Cleansing Agent: When dissolved in an enormous quantity of warm water, this chemical substance can be used as a cleansing agent.
Industries: Thiosulphate is popularly used for the dechlorinating of small water bodies such as aquariums, ponds, and so on. This inorganic substance is highly used in the production of patinas. It is widely used in gold extraction from its ores.
Medical Field: It is used in pharmaceutical preparations, including anionic surfactant helping in dispersion. Additionally, it is a crucial antidote to cyanide poisoning. It aids in treating ringworm plus overcoming the side-effects of chemotherapy.
Apart from the above applications, the thiosulphate structure shows that the compound is preferably used in water treatment, neutralizing bleach, leather tanning, photographic film processing, chemical heating pads, and so on.