Ozone Gas in Atmosphere
Ozone (O3) gas is a triatomic allotrope of oxygen and an important constituent of the upper atmosphere where it is formed by solar uv radiation of very high energy. It is a toxic blue gas freezing to purple solid at -193°C. Ozone is one of the strongest oxidizing agents that oxidize silver (I) to silver (II) and is used for converting olefins into aldehydes, ketones, or carboxylic acids. Ozone molecules absorbed moderately high energy uv radiation to protect the living worlds from harmful ultraviolet rays.
Nitrogen dioxide (NO2) from supersonic aircraft and industries catalyze the conversion of ozone to oxygen. Similarly, chlorofluorocarbons (CFC) photochemically decompose to give chlorine atoms which break the O3 molecule in a chain process. It may be observed that the nitrogen dioxide and chlorine atoms are continually regenerated which causes to damage the O3 balances in the upper atmosphere.
Structure and Chemical Bonding
Ozone has a planar structure with O-O-O angle equal to 116.78° and O-O chemical bond lengths equal to 1.28 Å. The central oxygen atom in the molecule is sp2 hybridized with one lone pair. The valence bond theory describes the two resonating forms of ozone molecule, each has a single bond on one side and a double bond with another side.
It is a polar molecule with a dipole moment of 0.53 D. If we count the valence electron, the molecule has a total of 6×3 = 18 valence electrons of which four are used for forming sigma-bonds. The central oxygen has one lone pair and the end oxygen atom has two lone pairs each. The remaining four-electron in ozone molecule used for forming pi-bonding.
Properties and Preparation
|Molecular formula||O 3|
|Molar mass||47,997 g / mol|
|Density||2.144 mg/cm3 at 0 °C|
|Melting point||−192.2 °C, −313.9|
|Boiling point||−112 °C, −170 °F|
|Solubility in water||1.05 g/L at 0 °C|
Ozone is a faint blue colour gas with a typical pungent smell. It is slightly soluble in water but more soluble in non-polar solvents like carbon tetrachloride. Both the liquid and gaseous forms of ozone are diamagnetic in nature and pure liquid is dangerously explosive chemicals. In acid solution, the potential of ozone being lower than those of a few oxidizing agents like fluorine, perxenate, and atomic oxygen. It may be estimated iodometrically by titrating iodine liberated form of a solution buffered with boric acid.
Ozone reacts with dry powdered alkali to formed red-brown paramagnetic ozonides. The stability of ozonide decreasing in the sequence of decreasing the cationic size (cesium > rubidium > potassium > sodium and barium > strontium > calcium) or increasing polarizing power. Lithium ozonide is known as amine like LiO3, 4NH3.
Ozone gas may be formed artificially or naturally. The stratospheric ozone layer is formed naturally through the interaction of solar ultraviolet (uv) radiation with molecular oxygen (O2). Artificially, the gas may be prepared by the silent electric discharge on oxygen and streaming out the gas quickly to avoid reconversion. It was also obtained by the anodic oxidation of a concentrated aqueous solution of perchloric acid at 50 °C. Pure ozone gas may be obtained by fractional distillation of a blue liquid mixture of O3-O2.