Oxides of sulphur preparation and properties, Group 16 P Block Elements
Sulphur dioxide (SO2) :
Sulphur dioxide can be prepared by the following methods
→ From sulphur: When sulphur is burned in presence of air or oxygen then wulphur dioxide is formed. With SO2 small amount approximate 6 to 8% of SO3 is also formed.
S8 + 😯2 → 8SO2
Laboratory Method : In laboratory, SO2 can be prepared when sodium sulphite reacts with dil HCl.
Industrial Preparation : Industrially SO2 can be prepared by roasting of sulphide ores such as iron pyrites organe blende.
→ The gas is dried, liquefied under pressure and stored in steel cylinders By heating sulphur with sulphuric acid : When sulphur is heated with sulphuric acid then sulphur dioxide is formed.
→ By heating copper or silver with concentrated sulphuric acid : When copper turning or silver is heated with concentrated sulphuric acid then so, is formed.
→ By the reaction of HCl with sodium sulphite or sodium hydrosulphide : On reacton between HCl and Na2 SO3 or NaHSO3 SO2 is formed.
→ By heating gypsum with carbon: When gypsum is heated with carbon at about 1000°C then sulphur dioxide is formed.
Properties (i) Physical Properties :
- It is a colourless gas with a pungent, auffocating smell.
- It is highly soluble in water.
- It liquefies at room temperature on applying 2 Atm, pressure.
- It liquefied at -10°C and solidify at – 76°C into snow like solid.
- It is heavier than air
- Liquid SO2 is a good solvent for sulphur, iodine, phosphorus etc.
Chemical Properties Oxides of sulphur
→ Acidic Nature : It forms sulphurous acid when dow in water
- It turns moist blue litmus red. It is known as anhydride of sulphurous acid.
- its acidic behaviour can be shown by the following reactions
→ Reaction with base: It readily reacts with sodium hydroxide and form sodium sulphite which again reacts with excess amount of soidum hydroxide forming sodium hydrogen sulphte.
Thermal decomposition : On beating strongly at 1473 K temeperature it decomposed into SO3 and S.
3SO2 → 2SO3 + S
On electric disintegeration it decomposes into SO3 and S.
3SO3 → 2SO+ O2
On electric disintegration it decompone into SO and O2
Reaction with oxygen : SO2 eacts with oxygen when it is heated in presence of V2O5 or platinum asbestos catalysis, then So is formed.
Renction with Chlorine : SO2 reacts with chlorine in presence of charcoal forming sulphuryl chloride SO2Cl2)
Reducing properties : Sulphur-di-oxide behaves as reducing agent. Its some important reducing properties are as follows
→ Reduction of halogen: It can reduce halogens into halogen acids or halide ions. As it can destroy the properties of chlorine so sulphur di-oxide is also known as anti-chlor
X2 + SO2 + 2H2O → 2HX + H2SO4
(where X = Cl, Brorl)
Reduction of lead dioxide into lead sulphate
Oxidising Properties : It behaves as mild oxidising agent. Some oxidising properties are given below:
It oxidises magnesium into magnesium oxide.
It oxidises iron into iron oxide and iron suiphide.
It can oxidises H2S into S.
2H2S + SO2 → 3S + 2H2O
It can oxidises carbon mono oxide into carbon-di-oxide.
2CO + SO2 → 2CO2 + S
It can oxidise stannous and mercurous salts into stannic and mercuric salts in presence of HCl.
→ Bleaching action Moist sulphur dioxide acts as mild bleaching agent. It bleaches naturally coloured subtances like flowers, vegntables, leaves etc. But its bleaching action is temporary as it is due to the reduction of substances. When bleached articles or substances are exposed to air, they remains its colour due to oxidation.
SO2 +2H2O H2SO4 +|2[H]
Vegetable colouring matter +[H] → Colourless vegetable matter
Reaction with hydrogen: SO2 oxidine hydrogen into water at 1000°C temperature.
→ Action of lime water. It can turn lime water milky, It is due to the formation of insoluble calcium sulphite. However, on passing time water in exces milliers disappears due to the formation of soluble sodium bisulphite.
Structure of SO2
in SO2 sulphur atom is sp2 hybridised. In it S-O-S bond ingle is 109,5°. Its shape is planar triangular. It has consting structures which are shown below
Uses Oxides of sulphur
- In refining of sugar and petroleum.
- In bleaching of the delicate articles such as wool, silk, straw etc.
- Used as a disinfectant, germicide and anti-chlor. (for removing excess chlorine)
- Used as preservative.
- In production of sulphuric acid, sodium hydrogen sulphite and calcium hydrogen sulphite ete.
- Used as a solvent for organic and inorganic chemicals.
- Used as a refrigerant.
Test of SO2
SO2 can be detected by the following tests :
- it is highly toxic was with a pungent and suffocating odour.
- It converts orange colour of acidified potassium dichromate into green
- It decfourises pink colour of potassium permangante.
Sulphur Tri Oxide (SO3)
→ From sulphur dioxide : SO2 is oxidised inpresence of V2O5 or finely divided platinum at 2 atm pressure and 700 K temperature into SO3.
2SO2 + O2 → 2SO3
→ From phosphorus pentoxide : On dehydrating conc. H2SO4 with phosphorus pentoxide, SO3 is formed.
Uses of Sulphur Tri Oxide (SO3)
- It is used in preparation of sulphuric acid and oleum
- Used as drying agent for various gases