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Trioxosulphate(IV) Acid, H2SO3


Trioxosulphate(IV) acid - H2SO3 is formed by the dissolution of SO2 in water.

SO2(g) + H2O(l) → H2SO3(aq)

Properties of H2SO3

Trioxosulphate(IV) acid is a colourless liquid, which smells strongly of SO2. It has all the reducing properties of SO2 in the presence of water.

The reaction of trioxosulphate(IV) acid, H2SO3 with alkali, such as sodium hydroxide, NaOH or potassium hydroxide KOH produces two salts: a normal salt and an acid salt.

2NaOH(aq) + H2SO3(aq) → Na2SO3(aq) + 2H2O(l) and

NaOH(aq) + H2SO3(aq) → NaHSO3(aq), + H2O(l)

The effect of acids on salts of trioxosulphate (IV):

Sulphur(IV) oxide, SO2 , is always given off when salts of trioxosulphate(IV) are warmed with dilute acids (such as hydrochloric acid and H2SO4.

This occurrence is sometimes used as a method to prepare SO2.

Na2SO3(aq) + H2SO4(aq) → Na2SO4(aq) + H2O(l) + SO2(g)

Note: Salts of trioxosulphate(IV) used in dilute acidified solutions show all the reducing properties of trioxosulphate(IV), or of sulphur(IV) oxide in water.





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