Sulphuric acid preparation and properties, Group 16 P Block Elements

Sulphuric acid preparation and properties, Group 16 P Block Elements

Sulphuric Acid (H2SO4) :

It is considered as the king of chemicals. In ancient days, it was called “oil of vitriol” as it has been prepared by the distillation of ferrous sulphate (Green Vitriol)

Sulphuric acid preparation and properties, Group 16 P Block Elements 1

Manufacture of sulphuric acid (Contact Proces) :

→ Production of sulphur-di-oxide : So, ein be prepared by oxidation of powdered uphur or by roasting of pyrites,

Sulphuric acid preparation and properties, Group 16 P Block Elements 2

→ Oxidation of Sulphur-di-oxide : SO2 is oxidised into SO3 in presence of atmospheric oxygen. The reaction is carried out in presence of V2O5 catalyst at 2 bar pressure and 720 K temperature.

Sulphuric acid preparation and properties, Group 16 P Block Elements 3

→ By increasing the production of SO3 we can increase the yield of sulphuric acid. By applying Le-Chateliers principle, we can get the better yield of sulphur trioxide by following conditions are maintained during manufacture.

→ Temperature. The reaction is exothermic bence at low temperature the reaction will go in forward direction, hence at 673-723 K temperature, the yield will be maximum

Pressure : High pressure will favour the process Thus, at 1.5 – 2bar pressure, the yield will be maximum

→ Catalyst: For better yield the presence of catalyst is compulsory because at low temperature, the reaction will be slow. Hence either vunndium pentaoxide (V2O5) or platinised asbestors is used as catalyst.

Sulphuric acid preparation and properties, Group 16 P Block Elements

Excess of Oxygen : For better yield of SO3O2 should be taken in excess.

Puricy of gases: For the prevention of poisoning of catalyst, the must be free from dust, moisture and As2O3.

Conversion of SO3 into H2SO4 production of So, it is absorbed in cone. H2SO4 to get oleum

Sulphuric acid preparation and properties, Group 16 P Block Elements 4

Oleum may be diluted with calculated amount of water to get H2SO4

Sulphuric acid preparation and properties, Group 16 P Block Elements 5

The sulphuric acid formed from this method is 96-98% pure.

Plant and its Working :

→ The plant employed for Contact process has been shown below in fig 7.38

Sulphuric acid preparation and properties, Group 16 P Block Elements 6

This plant consists of the following parts :

→ Pyrite burners : In this part sulphur or ironpyrite is oxidised in presence of excess of air and sulphur dioxide is formed.

S + O2 → SO2
4FeS2 + 11O2 → 2Fe2O3 + 8SO2

Sulphuric acid preparation and properties, Group 16 P Block Elements

→ Purifying Unit : The gases coming out from burners have the impurities of dust particles and arsenic oxides. Before passing the mixture from catalytie chamber it is quite necesary to remove these impurities. These impurities can be removed by passing the uses from following

  • Dust Chamber : In dust chamber, steam is passed from the top of the chamber. It helps in removing the dust from the gases by settling these particles
  • Coolers: In coolers the temperature of the is reduced to about 373 K
  • Scrubbers: Scrubber is a tower in whieh quartz is packed. In this tower, water is sprayed from the top so that dust particles and other water oluble impurities are removed.
  • Drying tower in this tower concentrated sulphuric acid is sprayed from the top of the tower so that the moisture present in case can be removed and the mixture may completely dehydrated.
  • Arsenie purifier : In this chamber freshly precipitated ferrie hydroxide is present which absorbs the impaurities of arsenic acide. Arsenie Oxide behave a poison for the catalyst.

→ Testing box: The gases coming out from the purification unit, are now pad through the testing box. Here the purity of gases is checked. For the testing of se, a strong beam of light is pred through the box. If the gases are impure then the path of beam will be invisible ie, the light will show Tyndall effect while if the gases are pure then the path of the beam will be invisible. In case if the gases are impure then the gases are furhter passed through purifying unit.

→ Contact tower: Now the pure ses are pre-heated up to about 723-823 K. Then gases passed into converter or contact tower. Contact tower is a cylindrical chamber which is made up of iron. In this chamber iron tubes are also present in which platinised asbestos is packed. But in many other cases V2O5 used because it is more efficient. In this converter, sulphur dioxide is oxidised to sulphur trioxide.

Sulphuric acid preparation and properties, Group 16 P Block Elements 7

This evolved beat is used in maintaining the temperature needed for the reaction. Thus, preheating is not needed any more.

→ Absorption tower : Sulphur trioxide coming from converter is now passed through this tower. The tower is packed with acid proof flint pieces. Pure concentrated sulphuric acid is sprayed from the top for the abeorption of sulphur triocide. After absorption of SO3 in conc H2SO4, oleum or fuming sulphuric acid is formed

Sulphuric acid preparation and properties, Group 16 P Block Elements 8

→ By diluting the oleum with calculated amount of water, concentrated sulphuric acid of desired concentration is obtained.

Sulphuric acid preparation and properties, Group 16 P Block Elements 9

→ SO3 is not abeorbed directly in water because it results forms a dense fog of sulphuric acid which cause much difficulty to the workers. Hence, wulphur trioxide is absorbed over sulphuric acid in order to make the procesa naler to handle.

Properties :

Physical Properties of Sulphuric acid

  • It is a colourless, corrosive and syrupy liquid called oil of vitriol
  • Its specific density is 1,84 pm at 20°C
  • Its freezing point is 10.5°C and boiling point is 317°C. The high boiling point of sulphuric acid is due to the presence of intermolecular hydrogen bonding which is shown below

Sulphuric acid preparation and properties, Group 16 P Block Elements 10

  • It also has very high viscosity due the presence of intermolecular hydrogen bonding
  • It has great affinity for water. It dissolves in water with exothermic process. When water is added to acid spurting takes place
  • because a lot of heat is produced during this process. Hence for diluting the acid, always add acid to water slowly and not water to acid.
  • It is highly corrosive and produces burns on the skin

Chemical properties of Sulphuric acid

The important chemical properties of sulphuric acid are discussed below

→ Dissociation : Sulphuric acid dissociates partially on heating upto 270°C temperature

Sulphuric acid preparation and properties, Group 16 P Block Elements 11

→ Acidic character: It is a strong dibasic acid. In aqueous solution, it ionises in two steps

Sulphuric acid preparation and properties, Group 16 P Block Elements 12

→ Higher value of Ka1 than Ka2 indicates that H2 SO4 is stronger acid than HSO4 In other words, we can say that HSO4 ion has lesser tendency to donate proton or H3O+ ion as compared to sulphuric acid. Since on disociation sulphuric acid forma two types of lona hence it reacts with base and forms two types of salt. These salts are knwon as acidic salts and normal salt.

Sulphuric acid preparation and properties, Group 16 P Block Elements 13
Sulphuric acid preparation and properties, Group 16 P Block Elements 14

→ As dehydrating agent: Concentrated sulphuric acid has strong affinity for water and it is highly hygroscopic in nature so it absorbs water ensily. Due to this reason it is used as a dehydrating agent. It ab orbe water from organic compounds like organic acids, sugars, starch, paper, wood, etc. Some examples are given below

Sulphuric acid preparation and properties, Group 16 P Block Elements 15

Drying of some gases: The gases like O2, N2 HCl, Cl2 etc Which do not react with cone. H2SO4 can be dried by conc. sulphuric acid.

→ Precipitation Reactions : Ba2+, Pb2+ Ca2+ Sr2+ etc. one can be precipitated in the form of sulpbate from their salt solutions.

Sulphuric acid preparation and properties, Group 16 P Block Elements 16

→ Oxidising properties : Hot and concentrated sulphuric acid behave a strong oxidising agent. The oxidising character of H2SO4 is due to the fact that it decomposes to give nascent oxygen.

Sulphuric acid preparation and properties, Group 16 P Block Elements 17

Some oxidising reactions are discussed below

→ Oxidation of copper metal In presence of sulphuric acid copper metal is oxidised into copper sulphate.

Sulphuric acid preparation and properties, Group 16 P Block Elements 18

→ Oxidation of silver metal: It oxidises silver metal into silver sulphate

Sulphuric acid preparation and properties, Group 16 P Block Elements 19

→ Oxidation of carbon. It oxidises carbon into carbon dioxide

C + 2H2SO4 → 2SO2 + 2H2O + CO2

→ Oxidation of sulphur : It oxidises sulphur into sulphur dioxide

S + 2H2SO4 → 3SO2 + 2H2O

Sulphuric acid preparation and properties, Group 16 P Block Elements

→ Oxidation of HBr and HI: It oxidises HBr into Br2 and HI into I2

2HBr + H2SO4 → Br2 + SO2 2H2O
2HI + H2SO4 → I2 + SO2 + 2H2O

→ Oxidation of phosphorus : It oxidises phosphorus into phonhar acid

Sulphuric acid preparation and properties, Group 16 P Block Elements 20

→ Oxidation of mercury : It oxidines mercury into HgSO4.

Sulphuric acid preparation and properties, Group 16 P Block Elements 21

→ Oxidation of naphthalene. In presence of mercury catalyst napthalene in oxidined into phthalic acid by sulphuric acid.

Sulphuric acid preparation and properties, Group 16 P Block Elements 22

→ Reaction with salts: (a) Dilute sulphuric acid can decomes bicarbonaten carbonates, sulphides, sulphites, nitritos eto at room temperature.

Sulphuric acid preparation and properties, Group 16 P Block Elements 23

Sulphuric acid preparation and properties, Group 16 P Block Elements 24

→ Hot concentrated sulphuric acid can decompose the Balts like chlorides, fluorides, nitrates, acetates, oxalates etc.

Sulphuric acid preparation and properties, Group 16 P Block Elements 25

→ Action with sulphur trioxide : Concentrated sulphuric acid absorbes wulphur trioxide and oleum or fuming sulphuric acid is formed

Sulphuric acid preparation and properties, Group 16 P Block Elements 26

→ Sulphonation Concentrated sulphuric acid and oleum reacts with aromotie compounds to form sulphonic acids.

Sulphuric acid preparation and properties, Group 16 P Block Elements 27

→ Action of Potassium ferrocyanide : Carbon mono oxide is formed

Sulphuric acid preparation and properties, Group 16 P Block Elements 28

→ Reaction with PCl5

Sulphuric acid preparation and properties, Group 16 P Block Elements 29
→ Reaction with potassium chlorate

Sulphuric acid preparation and properties, Group 16 P Block Elements 30

Structure of Sulphuric acid

Sulphuric acid as well as sulphate ion both have tetrahedral structure where sulphur atom is op hybridised

Sulphuric acid preparation and properties, Group 16 P Block Elements 31

Uses of Sulphuric acid

→ It is a very important industrial chemical and mainly used in manufacturing industrial products A nation’s industrial strength can be judged by the quantity od sulphuric acid. It is also known as king of chemicals. Ita main users follow

  • In production of fertilizers like ammonium sulphate, super phosphate etc.
  • In petroleum refining.
  • In leather industry for tanning.
  • In textile, paper and dying industries.
  • In manufacture of coal tar, dyea and a number of drugs and disinfectants.
  • In manufacturing of other acide such as orthophosphoric acid, nitric acid, hydrochloric acid etc.
  • In manufacturing of nitro cellulose.
  • In storage batteries.
  • in manufacturing of paints and pigments.
  • In cleansing metals before electroplating, enameling, galvanising and pickling.

Chemistry Notes

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

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

Oxoacids of Sulphur :

Sulphur forms various oroacide like H2SO3, H2S2O3, H2S2O4, H2S2O5, H2SO4, H2SO5 etc. Some of these acids are unstable and cannot be isolated in free state. They are known in aqueous solution or in the form of their alts The wtructures of these oxyacids are given below.

Sulphurous acid (H2SO3): Free acid does not exist. dipratic, strong reducing agent.

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 1

Sulphurie Acid (H2SO2): (Oil of vitriol): Stable, diprotic, dehydrating agent.

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 2

Peroxomono sulphuric acid or Caro’s acid (H2SO5)

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 3

Peroxodisulphuric acid or Marshall’s acid (H2SO2O8)

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 4

Thiosulphurie acld (H2S2O3): Pree acid does not exist but its salte.g. Na2S2O3 is found. All quite stable reducing agent.

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 5

Dithionic acid (H2S2O6) : Free acid is moderately stable but its salts are quite stable.

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 6

Pyrosuiphuric acid or oleum (H2S2O7) or disuiphuric acid strong oxidizing agent.

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 7

Polythionic Acid (H2S4O6)

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 8

Dithionous acid (H2S2O4)

Oxoacids of sulphur preparation and properties, Group 16 P Block Elements 9

Chemistry Notes

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

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.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 1

Industrial Preparation : Industrially SO2 can be prepared by roasting of sulphide ores such as iron pyrites organe blende.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 2

→ 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.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 3

→ By heating copper or silver with concentrated sulphuric acid : When copper turning or silver is heated with concentrated sulphuric acid then so, is formed.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 4

→ By the reaction of HCl with sodium sulphite or sodium hydrosulphide : On reacton between HCl and Na2 SO3 or NaHSO3 SO2 is formed.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 5

→ By heating gypsum with carbon: When gypsum is heated with carbon at about 1000°C then sulphur dioxide is formed.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 6

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

Oxides of sulphur preparation and properties, Group 16 P Block Elements 7

  • It turns moist blue litmus red. It is known as anhydride of sulphurous acid.
  • its acidic behaviour can be shown by the following reactions

Oxides of sulphur preparation and properties, Group 16 P Block Elements 8

→ 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.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 9

Thermal decomposition : On beating strongly at 1473 K temeperature it decomposed into SO3 and S.

3SO2 → 2SO3 + S

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

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.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 10

Renction with Chlorine : SO2 reacts with chlorine in presence of charcoal forming sulphuryl chloride SO2Cl2)

Oxides of sulphur preparation and properties, Group 16 P Block Elements 11

Reducing properties : Sulphur-di-oxide behaves as reducing agent. Its some important reducing properties are as follows

Oxides of sulphur preparation and properties, Group 16 P Block Elements 12

→ 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

Oxides of sulphur preparation and properties, Group 16 P Block Elements 13

Oxidising Properties : It behaves as mild oxidising agent. Some oxidising properties are given below:

It oxidises magnesium into magnesium oxide.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 14

It oxidises iron into iron oxide and iron suiphide.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 15

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.

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

→ 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]

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

Vegetable colouring matter +[H] → Colourless vegetable matter

Reaction with hydrogen: SO2 oxidine hydrogen into water at 1000°C temperature.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 17

→ 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.

Oxides of sulphur preparation and properties, Group 16 P Block Elements 18

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

Oxides of sulphur preparation and properties, Group 16 P Block Elements 19

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.

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

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.Oxides of sulphur preparation and properties, Group 16 P Block Elements 20

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

Sulphur preparation and properties, Group 16 P Block Elements

Sulphur preparation and properties, Group 16 P Block Elements

Sulphur :

It is the second member of group – 16 It is a typical non-metal. Its atomic number is 16 and electronic configuration is 1s2 2s2 2p6 3s2 3p4.

Occurrence :

→ Sulphur occurs in the earth’s crust to extent of 0.06%. It coeurs in nature in both combined and free states. In free state it is found in the volcanic regions of Japan, South America. Sicily and Russia..

Sulphur preparation and properties, Group 16 P Block Elements

→ In combined state, it exist in the form of sulphates and sulphides. Some example are given below

  • Epsom salt (MgSO4 . 7H2O)
  • Galena (PbS)
  • Copper pyrites (CuFeS2)
  • Iron pyrites (Fes2)
  • Zinc blende (ZnS)
  • Cinnabar (HgS)
  • Gypsum (CaSO4 . 2H2O)
  • Barytos (BaSO4)

→ Traces of sulphur also occurs as hydrogen sulphide (H2S) gas coming out from the volcanoes. Some organic substances like proteins, hair, onion, eggs, garlic, wool etc, also have small percentage of sulphur.

Allotropes of Sulphur

exhibit in various allotropic forms. The various allotropes of sulphur are discussed below.

→ Orthorhombic or Octahedral or c-Sulphur or Yellow sulphur or Rhombic Sulphur: It is a common form of sulphur. It can be prepared when the solution of sulphur in carbon-di-sulphide (CS2), taken in a dish, is evaporated slowly then crystals of sulphur are appeared in dish.

Sulphur preparation and properties, Group 16 P Block Elements

→ It is most stable and common allotropic form of sulphur. It is yellow in colour. It a melting point is 386.8KIts specific gravity is 2.06 pem! It is insoluble in water but soluble in benene, akohol and other. It is highly soluble in carbon di sulphide, it has very little electrical and thermal conductivity. It exist as S, molecule which has puckered ring like or crown shaped structure.

Sulphur preparation and properties, Group 16 P Block Elements 1

→ Monoclinic or prismatie ors-Sulphur : Monoclinic sulphur is prepared by melting the sulphur ina china dish and cooling till the crust is formed. On removing the crust needle shaped crystals of monoclinic sulphur are obtained.

→ This allotropic form of sulphur is dull yellow in colour. Its specific gravity is 1.98 g/cm3. Its melting point is 393 K. It is insoluble in water but soluble only in carbon disulphide (CS2), It slowly changes into rhombie sulphur. It also exist ass, molecule with puckered ring like or crown shaped structure but it differs from the rhombic sulphur in the symmetry.

Sulphur preparation and properties, Group 16 P Block Elements 2
Sulphur preparation and properties, Group 16 P Block Elements 3

In contrast, below 360 K temperatured-sulphur is stable. This temperature is known as transition temperature.

Sulphur preparation and properties, Group 16 P Block Elements

→ Plastic Sulphur or Amorphous sulphur or y Sulphur : When molten sulphur is poured into cokl water then soft rubber like mass is obtained which is known as plastie sulphur. This super cooled liquid is insoluble in water as well as carbon disulphide (CS2). It i anamorphous form of sulphur. It has no sharp melting point. Its specific gravity in 1.95 g/cm3. It has zig-zag chain like structure.

Sulphur preparation and properties, Group 16 P Block Elements 4

→ Colloidal Sulphur or & Sulphur It can be obtained from any oxidising agent or sodium thio sulphate. When sodium thiosulphate reacts with dilute hydrochloric acid then colloidal sulphur is obtained.

Sulphur preparation and properties, Group 16 P Block Elements 6

→ Cyclo S6-20 form : In this form sulphur exist as a ring where S6 occupy a chair form. Cyclo-S6 form of sulphur is also known as Engel’s sulphur or e-sulphur

Sulphur preparation and properties, Group 16 P Block Elements 5

→ Catena S(n): It has chain like structure. This allotrope is formed only at high temperature. It exists in liquid state. Sometimes in this form, sulphur exists in vapour phase Here n = 2 – 5.

Sulphur preparation and properties, Group 16 P Block Elements

→ At about 1000K temperature S2 species predominate. Like dioxygen (O2)S2 le paramagnetic and blue coloured. It is due to the presence of unpaired electron in π antibonding molecular orbital.

Chemistry Notes

Ozone preparation and properties, Group 16 P Block Elements

Ozone preparation and properties, Group 16 P Block Elements

Ozone : 

Ozone is an allotrope of oxygen gas. It is higly reative gas. It is present in the upper atmosphere about 20 km away from the earth surface. The layer of ozone acts as a blanket and protects us from harmful ultraviolet rays.

Preparation From Siemen-Brodie’s Ozonizer

→ When silent (sparkless) electrie discharge is passed through pure, cold and completely dry oxygen at 298 K temperature, then one is prepared. The appartus in which one is prepared is known as conizer.

Ozone preparation and properties, Group 16 P Block Elements 1

→ The preparation of none from oxygen is an endothermia reaction hence during its preparation the use of silent electric discharge is compulsory so that it can be protected from decomposition. For the preparation of pure none (b.p 385 K), batteries are used in azoniser. Pure one is condensed in a receiver surrounded by liquid oxygen

Ozone preparation and properties, Group 16 P Block Elements 2

Explanation of Ozone

→ Siemen’s zoniser is made up of two concentric tubes which are sealed at one end. There is an inlet for passing pure dry cygen and an outlet for release of cooniand oxygen or one. Outer surface of the outer tube and inner surface of the inner tube is coated with tin foil.

Ozone preparation and properties, Group 16 P Block Elements

→ This inner and outer contings of tin foil are connected with terminals of induction coil Now a slow and silent stream of pure and dry Oxygen is persed through the space between the two tubea. This stream of pure and dry oxygen is subjected to the silent electrical discharge.

→ Some of the oxygen gets converted into ozone forming the product which has 15-25% Rone. For increasing the yield of product, following precautions must be taken

  • Sparkless discharge should be passed
  • Dioxygen should be pure and dry
  • Temperature should be kw
  • Osonizer should be free from moisture

Ozone preparation and properties, Group 16 P Block Elements

Purification of ozonised oxygen :

To get pure onone, the ononised oxygen obtained from the above method is surrounded by liquified air. As a result, ozone (b.p. 161. 2K) is condensed first and then Oxygen (b.p. 90°K). The small amount of oxygen present with osone can be separated by fractional distillation.

Physical properties of Ozone

  • Pure ozone is a pale blue gas having characteristic pungent smell.
  • It is a dark blue liquid and violet black solid.
  • When inhaled in small concentration it is harmless however if the concentration rises above about 100 parts per million then
  • breathing becomes uncomfortable resulting in headache and nausen.
  • It is heavier than air. Ita vapour density is 24.
  • Its boiling point is 385 K and melting point is 24K
  • It is slightly soluble in water but it is highly soluble in organic solvents like benzene, carbon tetrachloride etc.
  • Ozone is dimagnetic in nature.
  • One is thermodynamically unstable with respect to oxygen but at high concentration it may become explosive.

Chemical Properties of Ozone

Some important chemical properties of one are discussed below

  • Action with litmus : Ozone is neutral towards litmus
  • Decomposition: Purecone decompose at room temperature. However on heating above 473K temperature it decomposes into oxygen gas.

Ozone preparation and properties, Group 16 P Block Elements 3

The decomposition of one can be entalyzed in presence of MnO2 Peblack, CuO etc.
Oxidising properties : Ozone is a powerful oxidising agent, because it easily liberates nascent oxygen.

Ozone preparation and properties, Group 16 P Block Elements 4

Some important oxidising properties of osone are as follows

Oxidation of lead sulphide : Omne oxidises black lead sulphide into white lead sulphate.

Ozone preparation and properties, Group 16 P Block Elements 5

Similarly Cds, ZnS and Mns are also oxidised into their corresponding sulphater

Oxidation of H2S : Owne oxidises H2S into sulphur.

Ozone preparation and properties, Group 16 P Block Elements 6

Oxidation of KI: Oxone oxidises KI into I2

Ozone preparation and properties, Group 16 P Block Elements 7

Similarly HBr, HI also oxidised into Br2 and I2 respectively

Oxidation of HCl:One oxidise HCl into Cl2 i.e., halogen acids are oxidine into corresponding halogens.

Ozone preparation and properties, Group 16 P Block Elements 8

Oxidation of Nitrites. In presence of ozone, nitrites are oxidised into nitrate.

Ozone preparation and properties, Group 16 P Block Elements 9

Oxidation of Silver : Ozone oxidised silver into silver oxide

Ozone preparation and properties, Group 16 P Block Elements 10

Oxidation of ferrous salts: Ozone ocidises acidified ferrous salts to ferrie salts.

Ozone preparation and properties, Group 16 P Block Elements 11

Oxidation of potassium ferrocyanide : One oxydises potassium ferrocyanide in to potassium ferricyanide.

Ozone preparation and properties, Group 16 P Block Elements 12

Oxidation of potassium manganate : Ozone oxidises potassium manganate in to potassium permanganate.

Ozone preparation and properties, Group 16 P Block Elements 13

Oxidation of non-metals non-metal into their oxy-acids.

Moist iodine is oxidised into iothc acid

Ozone preparation and properties, Group 16 P Block Elements 14

Sulphur is oxidised into sulphuric acid

S + 3O2 + H2O → H2SO4 + 3O2

Moist phosphorus is oxidised into phosphoric acid

Ozone preparation and properties, Group 16 P Block Elements 15

Oxidation of metalloids: Ozone oxidises certain metalloids into their respective oxyacids
For example

Ozone preparation and properties, Group 16 P Block Elements 16

Reaction with mercury : Oxone oxidises mercury into mercurous oxide.

Ozone preparation and properties, Group 16 P Block Elements 17

→ During above given reaction mercury loves its meniscus and sticks to the sides of capillary. This process is known as tailing of mercury. 5. Estimation of ozone : When one reacts with an excess of potassium iodide solution buffered with a borate buffer pH 9.2), iodine is liberated which can be titrated against the standard solution of sodium thiosulphate. This is quantitative method for estimating one gas.

Ozone preparation and properties, Group 16 P Block Elements 18

Reducing Properties : Unone also acts as reducing agent. For example.

Hydrogen peroxide is reduced in to water in presence of ozone.

Ozone preparation and properties, Group 16 P Block Elements 19

Sodium peroxide is reduced into sodium oxide in presence of ozone.

Ozone preparation and properties, Group 16 P Block Elements 20

Bleaching action: It is a good bleaching agent. The bleaching action is due to its oxidising action on the organic matter.

Ozone preparation and properties, Group 16 P Block Elements 21

It can bleach oil, ivory, starch, flour, waxes, wood pulp etc.

Ozone preparation and properties, Group 16 P Block Elements

→ Formation of ozonide : Osone acts with unsaturated organic hydrocarbons containing double or triple bonds and a product is formed, which is known as ovonide. This ozonide reacts with water in the presence of Zn and form carbonyl compounds. The process in known as cronolysis. Some examples are given below:

Ozone preparation and properties, Group 16 P Block Elements 22

Ozone preparation and properties, Group 16 P Block Elements 23

Depletion of ozone layer: Ozone layer is present in the stratepheme which is about 11 – 150 km above from earth’s surface

Formation of ozone layer

Ozone preparation and properties, Group 16 P Block Elements 24

→ The chemicals responsible for the destruction of ozone layer are NOx released from aircraft) and chloro Eluorocarbons (CFC)(s)] used as aerosol propellants, in refrigerators and in air conditioner. The mechanism of depletion of none layer enn be represented as.

Ozone preparation and properties, Group 16 P Block Elements 25

→ Steps (ii) and (iii) are repeated again and again causing the destruction of ozone, Because of the destruction of czone layer, its concentratin has fallen down, which causes ozone hole.

Ozone preparation and properties, Group 16 P Block Elements

→ Due to the formation of oxone hole the high radiation ultraviolet rays are in a position to pass through this hole, which have a direct de to our earth. These rays are harmful to human beings and causes skin cancer, loss of wight and effect our immune system

Structure of Ozone

Ozone shows resonating structures

Ozone preparation and properties, Group 16 P Block Elements 26

→ The central oxygen atom is op hybridised, so the shape of ozone is angular with bond angle 116.8°. Due to the, presence of resonance both the bond has similar bopd length i.e. 127.8pm which is intermediate to single 0-0 (148 pm) and double 0=0 (110 pm) bond length which proves the presence of resonance.

Ozone preparation and properties, Group 16 P Block Elements 27

Uses of ozone

  • As a strong oxidising agent.
  • As a germicide and disinfectant.
  • Used for sterilizing drinking water.
  • In preparing artificial silk and camphor.
  • In bleaching oil, delicate farbrica, starch and ivory etc.
  • Used for purifying air of crowded places such as cinema, underground railways, tunnels, mines
  • Used in manufacturing of potassium permanganate, artificial silk, synthetic camphor etc.

Chemistry Notes

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

Dioxygen (O2) :

→ Dioxygen is the most abundant element in the earth’s crust (46.5%). Karl Scheele was the first to prepare it by heating mercuric oxide in 1772. Later on Joseph Priestly also prepared it.

→ Lavosier first time named it oxypen for = acid. gennas-maker). In atmosphere, dioxygen (O2)is nearly 216 by volume and the rest is dinitrogen.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

Preparation of  Dioxygen

Dioxygen can be prepared as shown below:

By heating the Salts Containing Oxygen :

The salts containing oxygen when heated strongly dioxygen is evolved.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 1

Laboratory Method : In laboratory, dioxygen gas can be prepared by thermal decomposition of potassium chlorate.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 2

By Heating Metallic Oxides : On heating the oxides of mercury, lead, silver, managenese etc. dioxygen is prepared.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 3

By decomposition of Peroxide : Hydrogen peroxide is decomposed easily in presence of finely divided metals or manganese dioxide

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 4

By the action of concentrated Sulphuric acid on certain oxygen compounds When concentrated sulphuric acid is reacted with some oxygen rich compounds then dioxygen gas is released

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 5

By photosynthesis : Oxygen gas can also be prepared by photosynthesis, taking place in the plants.

→ Industrial Preparation : Industrially dioxygen can be prepared by the following two methods: ) By electrolysis of water On clectrolysis of aedified water, using platinum electrodes or alkaline water using nickel electrode, dioxygen as is liberated at anode.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 6

→ By liquid air: First of all carbon dioxide and water vapours are removed from air then rest of the gases are liquified under high pressure and low temperature. This liquid air is now subjected to distillation then liquid dinitrogen (b.p. 77.2 K) distilled out first, leaving behind liquid oxygen (b.p.90 K). Now this liquid oxygen is recovered.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

→ By electrolysis of Ba(OH)2 Pure dioxygen can be prepared by electrolysis of Ba(OH)2 Rolution using nickel electrode then oxygen gas is obtained at anode.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 7

From Sodium Peroxide Dioxygen can be prepared in laboratory by the action of water on sodium peroxide.

2Na2O2 + 2H2O → 4NaOH + O2

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements

Dioxygen can also be prepared by the action of acidified potassium permanagate on sodium peroxide.

2KMnO4 + 5Na2O2 + 8H2SO4 → K2SO4 + 2MnSO4 + 5Na2 SO4 + 5O2

Properties :

Its physical and chemical properties are as follows:

Physical Properties of Dioxygen

  • It is colourless, odourless and tasteless gas.
  • It is neutral towards litmus paper.
  • It is slightly heavier than air. It is slightly soluble in water and its solubility is about 3.08 cm2 in 100 cm3 of water at 298 K and one atmospheric pressure. But this small amount of disolved oxygen is sufficient to sustain marine and aquatic life.
    It liquiefies at 90 K and freeses at 55K.
  • There are three isotopes of oxygen. They are
    Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 8
  • It is paramagnetic in nature. Its paramagnetism is due to the presence of unpaired electrons. Its molecular orbital configuration is as follows:

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 9

Chemical Properties of Dioxygen :

Some important chemical properties are as follows:

Action of Litmus Dioxygen is neutral to litmus.
Reaction with Metals except some metals like Ag, Au, Pt, it reacts with all other metals to for respective oxides. For examples,

Active metals like Na, Ca react at room temperature to form respective oxides.

4Na + O2 → 2Na2O
2Ca + O2 → 2CaO

Sodium also reacts with dioxygen at 575 K to form sodium peruxide

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 10

Magnesium burns in diexygen to form magnesium oxide

2Mg + O2 →2Mgo

Metals like Al, Fe reacts only on heating

4Al + 3O2 → 2Al2O3
4Fe + 3O2 → 2Fe2O3

Reaction with non-metals: It do not react with noble age. Some reactions with non-metals are as follows

Reaction with hydrogen

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 11

Reaction with carbon, nitrogen and phosphorus

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 12

Reaction with sulphur

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 13

Reactions with compounds : Dioxygen oxidises a variety of compounds. Some important actions are & follows

Reaction with aminonia as : Dioxygen axidises ammonia to nitrie oxide in the presence of platinum gauze catalyst at 1100 K.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 14

With hydrogen chloride Dioxygen reacts with HCl in presence of cuprie chloride catalyst at 700 K.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 15

With sulphur dioxide: In presence of oxygen SO2 la oxidised into SO2 at 728 K in the presence of V2O5 or finely divided platinum.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 16

With carbon disulphide : Carbon disulphide on heating with dioxygen form sulphur dioxide and carbon dioxide.

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 17

With carbon monooxide: Carbon monoxide when oxidised with oxygen then carbon dioxide is formed

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 18

Reaction with hydrocarbons : Saturated as well as unsaturated hydrocarbone burn in excre of air or oxygen to form carbon dioxide and water. These reactions are known as combustion reactions. These reactions are exothermic in nature

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 19

Oxidation Reaction. If hydrocarbona are oxidised in presence of catalyst, different products are formed. Here the oxidation is done in limited amount of oxygen

Dioxygen or oxygen preparation and properties, Group 16 P Block Elements 20

Uses of Dioxygen

  • It is used in artifical respiration when it is mixed with helium or carbon dioxide
  • It is used as an oxidiser in the space rockets.
  • Liquid dioxygen mixed with finely divided carbon acts like dynamite in coal mining.
  • The isotope of oxygen (0-18) is used in studying the mechanism of certain reactions.
  • It is used in the manufacture of nitric acid, sulphuric acid, ethylene oxide, phenol, SO, etc. va) It is used in the production of oxy-hydrogen or xy-acetylene flame which is used in welding.
  • It is used as an oxidising agent in several reactions.
  • It is essential for the respiration by human being Dioxygen combines with our blood and forme oxy haemoglobin. In the form of oxyhaemoglobin it is carried to various parts of our body where it take part in oxidation reactions.
  • The energy releseed during oxidation reactions is quite essential to sustain life.

Chemistry Notes