Acid is a water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt. A corrosive liquid with a pH less than 7; a solution of in water of a substance that releases hydrogen ions.
In other word, it is a compound which contains replaceable hydrogen atom or atoms, a part or whole of which can be replaced by means of a metal or a positive radical. For Example: HCl, HNO3, H2SO4 etc are acids because they contain replaceable hydrogen atom or atoms.
Theory related to the Acids
Arrhenius’s Ionic theory: This theory was introduced in 1887 by the Swedish scientist Svante Arrhenius, that acids are substances that dissociate in water to yield electrically charged atoms or molecules, called ions, one of which is a hydrogen ion (H+), and that bases ionize in water to yield hydroxide ions (OH−). It is now known that the hydrogen ion cannot exist alone in water solution; rather, it exists in a combined state with a water molecule, as the hydronium ion (H3O+). In practice the hydronium ion is still customarily referred to as the hydrogen ion.
Bronsted and Lowry theory: This theory is also called proton theory of acids and bases, a theory, introduced independently in 1923 by the Danish chemist Johannes Nicolaus Bronsted and the English chemist Thomas Martin Lowry, stating that any compound that can transfer a proton to any other compound is an acid, and the compound that accepts the proton is a base. A proton is a nuclear particle with a unit positive electrical charge; it is represented by the symbol H+ because it constitutes the nucleus of a hydrogen atom.
Lewis’s electronic theory: In 1923 G. N. Lewis gave this theory in which he suggested that the reaction between H+ and OH- ions. In the Brnsted model, the OH- ion is the active species in this reaction it accepts an H+ ion to form a covalent bond. In the Lewis model, the H+ ion is the active species it accepts a pair of electrons from the OH- ion to form a covalent bond.
In the Lewis theory of acid-base reactions, bases donate pairs of electrons and acids accept pairs of electrons. A Lewis acid is therefore any substance, such as the H+ ion, that can accept a pair of nonbonding electrons. In other words, a Lewis acid is an electron-pair acceptor. A Lewis base is any substance, such as the OH- ion, that can donate a pair of nonbonding electrons. A Lewis base is therefore an electron-pair donor.
Characteristics of Acids
Types of Acids
Uses of Acids
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