Applied Chemistry-I by Gurcharan Dass

Applied Chemistry-I by Gurcharan Dass
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Applied Chemistry-I by Gurcharan Dass

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Publisher: Vayu Education
ISBN: 9789383137152
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Contents 1. ACIDS-BASES, CATALYSIS ................................................................................ 1-10 2. POLLUTION ........................................................................................................ 11-23 3. ELECTRO CHEMISTRY AND CORROSION ................................................ 24-36 4. ORGANIC COATINGS ....................................................................................... 37-56 5. COLLOIDS AND CERAMICS ........................................................................... 57-58
Chapter-1
1
Acids-Bases, Catalysis 1.1 THEORY OF ACIDS AND BASES The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically An acid substance is one which can employ an electron lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H3O is a Lewis acid, since it can accept a lone pair, completing its stable form, which requires two electrons. A Lewis base, then, is any species that donates a pair of electrons to a Lewis acid to form a Lewis adduct. For example, OH and NH3 are Lewis bases, because they can donate a lone pair of electrons. Some compounds, such as H2O, are both Lewis acids and Lewis bases, because they can either accept a pair of electrons or donate a pair of electrons, depending upon the reaction.
Reformulation of Lewis Theory Lewis had suggested in 1916 that two atoms are held together in a chemical bond by sharing a pair of electrons. When each atom contributed one electron to the bond it was called a covalent bond. When both electrons come from one of the atoms it was called a dative covalent bond or coordinate bond. The distinction is not very clear-cut. For example, in the formation of an ammonium ion from ammonia and hydrogen the ammonia molecule donates a pair of electrons to the proton the identity of the electrons is lost in the ammonium ion that is formed. Nevertheless, Lewis suggested that an electron-pair donor be classified as a base and an electron-pair acceptor be classified as acid. A more modern definition of a Lewis acid is an atomic or molecular species with a localized empty atomic or molecular orbital of low energy. This lowest energy molecular orbital LUMO can accommodate a pair of electrons.
1.2 CATALYSIS A catalyst is defined as a substance which increases the rate of a chemical reaction without being consumed in the process. The phenomenon of increase in the rate of a reaction with the help of a catalyst is known as catalysis.
2
Applied Chemistry - I
A B Catalyst
Y Z Catalyst
Presence of certain substances in exceedingly small amounts often considerably affects the activity of catalyst.
Fig.