What is Sodium Thiosulphate?

Sodium thiosulphate is known as disodium salt. it is an inorganic salt that is also available in the pentahydrates.

This is a chemical substance. it has a chemical formula of Na2S2O3.

It appears as a bright white colourless crystal or even in powder form.

The substance is known to possess Alkaline nature when decomposed to sulphide and sulfate in the air.

Sodium thiosulfate readily dissolves in water giving thiosulfate ions,

This is a one of the useful reducing agents. the important chemical reaction.


The Copper (II) sulfate dissolves to give the cupric ion.

The cupric particles is know as stronge oxidizing agents.

It is water-soluble substance and is also soluble in oil of turpentine.

The substance has a melting point of about 48 to 52 C.

You know, this chemical substance is very highly stable.

This chemical substance is highly stable in nature.

The chemical has a density measuring about 1.667 g/mL.

Sodium thiosulphate structure?

Sodium Thiosulphate has a chemical formula of Na2S2O3 and the molar mass of about 158.11 g/mol. The substance well exists in the form of pentahydrate salts (Na2S2O3.5H2O), having a molar mass measuring about 248.18 g/mol.

The sodium Thiosulphate is an ionic compound which consists of two cations of sodium atom (Na+) and a negatively charged anion of thiosulfate (S2O3-). Here the central atom consisting of sulphur bonds to the three oxygen atoms and also another atom of sulphur, all these through a single and also double bonds possessing resonance character. The solid also exists in a monoclinic crystalline structure.

Basic concepts of sodium thiosulphate

It is also called sodium hyposulfite. Sodium thiosulfate is known as hypo or hyposulfite of soda.

Sodium thiosulfate is an important inorganic salt with several medical uses.

It is also called sodium hyposulfite.


Physical properties

(1) it is a colourless.

(2) it is crystalline in nature.

(3) This is a chemical in nature in which it is also known as efflorescent substance.

(4) The chemical formula is Na2S2O3.5H2O.

(5) It is soluble in water.

Chemical Properties

(1) Action of Heat

On heating it decomposes to give sulphur dioxide, hydrogen sulphide and sulphur.

(2) Action of dilute acids

Dilute acids decompose it with evaluation of sulphur dioxide and precipitation of sulphur.

Na2S2O3 + 2 HCl – 2NaCl + SO2 + S + H2O

(3) Action of silver halides

Silver halides are dissolved by sodium thiosulphate solution.

AgBr + 2Na2S2O3 – Na[Ag(S2O3)2]

(4) Action of silver nitrate solution

According to this, it give silver nitrate, silver nitrate gives with a very dilute solution of precipitate which fast changes colour to yellow, brown, and finally, results black colour are obtained due to the formation of silver sulphide.

Na2S2O3 + 2AgNO3 – Ag2S2O3 + 2NaNO3

Ag2S2O3 + H2O – Ag2S + H2SO4

(5) with ferric chloride solution

On addition of a few drops of ferric chloride to thiosulphate solution, According to this, violet colouration is obtained due to the formation of ferric thiosulphate.

3Na2S2O3 + 2FeCl3 Fe(S2O3)3 + 6NaCl

The violet colour disappears quickly due to the reduction of ferric chloride by thiosulphate. this shift the above equilibrium to the left.


(1) Sodium Thiosulphate is prepared by boiling sodium sulphate solution with flowers of sulphur and strirring till the alkaline reaction has disappeared.

For example,

Na2SO3 + S – Na2S2O3

The excess of sulphur is filtered off and the filtrate evaporated to crystallization when crystals of sodium thiosulphate, Na2S2O3.5H2O separate on slow cooling.

Sodium sulphate used above is prepared from sodium carbonate.

A concentrated solution of sodium carbonate is prepared. One half of the saturated with sulphur dioxide and the other half of the solution iss then added when we get sodium sulphate.

Na2CO3 + 2SO2 + H2O – 2NaHSO3 + CO2

2NaHSO3 + Na2CO3 – 2Na2SO3 + H2O + CO2

(2) Sodium thiosulphate is also formed together with sodium sulphide when sulphur is boiled with sodium hydroxide solution.

6NaOH + 4S – NaS2O3 + 2Na2S + 3H2O

Sodium thiosulphate Uses

(1) In textile industry : During bleaching sodium thiosulphate is used as antichlor.

(2) It is used in the exctration and silver from themselves.

(3) In the laboratory – it is used for the volume estimation of lodine and as a reagent.

(4) In medicine – Sodium thiosulphate is also used in medicine.

(5) In photography – it used in photography for fixing.


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