Oxides of sulphur Oxides of sulphur preparation and properties

Oxides of sulphur preparation and properties, Group 16 P Block Elements

Sulphur dioxide (SO₂) :

Preparation :

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)

Preparation :

→ 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

Chemistry Notes