OXIDES OF SULPHUR

Liquid sulphur dioxide in small glass siphons may be purchased from

chemical manufacturers. Sulphur dioxide may be dried with concentrated

sulphuric acid, and collected either over mercury or by the upward

displacement of air.

In industry scale sulphur dioxide is made by burning sulphur in air . The

gaseous products of combustion pas up to a tower to meet a steam of cold

water which dissolves out the sulphur dioxide. The sulphur dioxide is

boiled out of the resulting solution dried by refrigeration and by exposure

to sulphuric acid, liquefied by compression and stored in steel cylinders.

Sulphur dioxide is colorless, heavy gas with an acrid, suffocating

smell,B.Pt.-10? , M.Pt.-72.7?.at 15? sulphur dioxide may be condensed to

colorless, heavy liquid by pressure of 2.5 atmospheres.

Sulphur dioxide reacts with chlorine in the presence of charcoal to yield

sulphuryl chloride , and with oxygen in the presence of platinum to yield

sulphur trioxide. sulphur dioxide absorbs by alkalis to yield sulphite and

bisulphite.

Sulphur dioxide dissolves in water at .15? , 1 volume of water dissolves

45 volume of the gas. the solution probably contains the weak acid

H2SO3, but the acid has not been isolated.

An aqueous solution of sulphur dioxide used in the lab. As a reducing

agent

2KMnO4+5 SO2 + 2H2O= K2SO4+ 2MnSO4+2H2SO4

Sulphur dioxide in some conditions can react as an oxidizing agent ;

2H2S+ SO2 = 2H2O+ 3S

At high temperatures sulphur dioxide oxidizes carbon to carbon dioxide,

and many metallic sulphides to sulphates.

Sulphur trioxide: is made by passing a mixture of sulphur dioxide and air

over platinum heated to 450?.

Sulphur trioxide may be also prepared by the thermal decomposition of:

1- ferric sulphate

Fe2(SO4)3= Fe2O3+3SO3

2- pyrosulphuric acid or sodium pyrosulphate

Na2S2O7= Na2SO4 + SO3

3- a mixture of concentrated sulphuric acid and phosphorus pentoxide

P4O10+ 2 H2SO4= 2SO3+ 4 HPO3