Ozone preparation and properties, Group 16 P Block Elements
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.
→ 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
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.
→ 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
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.
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.
Some important oxidising properties of osone are as follows
Oxidation of lead sulphide : Omne oxidises black lead sulphide into white lead sulphate.
Similarly Cds, ZnS and Mns are also oxidised into their corresponding sulphater
Oxidation of H2S : Owne oxidises H2S into sulphur.
Oxidation of KI: Oxone oxidises KI into I2
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.
Oxidation of Nitrites. In presence of ozone, nitrites are oxidised into nitrate.
Oxidation of Silver : Ozone oxidised silver into silver oxide
Oxidation of ferrous salts: Ozone ocidises acidified ferrous salts to ferrie salts.
Oxidation of potassium ferrocyanide : One oxydises potassium ferrocyanide in to potassium ferricyanide.
Oxidation of potassium manganate : Ozone oxidises potassium manganate in to potassium permanganate.
Oxidation of non-metals non-metal into their oxy-acids.
Moist iodine is oxidised into iothc acid
Sulphur is oxidised into sulphuric acid
S + 3O2 + H2O → H2SO4 + 3O2
Moist phosphorus is oxidised into phosphoric acid
Oxidation of metalloids: Ozone oxidises certain metalloids into their respective oxyacids
Reaction with mercury : Oxone oxidises mercury into mercurous oxide.
→ 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.
Reducing Properties : Unone also acts as reducing agent. For example.
Hydrogen peroxide is reduced in to water in presence of ozone.
Sodium peroxide is reduced into sodium oxide in presence of ozone.
Bleaching action: It is a good bleaching agent. The bleaching action is due to its oxidising action on the organic matter.
It can bleach oil, ivory, starch, flour, waxes, wood pulp etc.
→ 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:
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
→ 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.
→ 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.
→ 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
→ 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.
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.