write note on Arrehenius theory of acid and bases
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The Arrhenius Theory of Acid and Bases
Abstract
Swedish Svante Arrhenius, in 1884 proposed the concept of acid and base based on the theory of ionization. According to Arrhenius, the acids are the hydrogen-containing compounds which give H+ ions or protons on dissociation in water and bases are the hydroxide compounds which give OH− ions on dissociation in water. This concept is only applicable to those compounds which dissolved in aqueous solution (or you can say where water is the solvent). It covers many common acids, bases and their chemical reactions, but there are also other compounds that have the characteristics of acids and bases but they do not fit into Arrhenius concept.
Theory
According to Arrhenius theory, acid is a substance that gives H+ ion on dissolving in the aqueous solution. It increases the concentration of H+ ions in the solution. The base is a substance that ionizes OH– ion by dissolving in the aqueous solution. The concentration of OH- ions is high in the solution.
Arrhenius Acids
Arrhenius acid in the aqueous solution increases the concentration of protons or H+ ions. For example, hydrochloric acid in the water. HCl undergoes dissociation reaction to produce H+ ion and Cl– ion, as explained below. The concentration of the H+ ions is increased by forming hydronium ion.
HCl (aq) → H+(aq) + Cl–(aq)
HCl (aq) + H2O(l) → H3O+(aq) + Cl–(aq)
Other examples of Arrhenius acids are listed below
NHO3(aq) + H2O(l) → H3O+(aq) + No3–
In this reaction, nitric acid dissolves in aqueous water to give hydrogen and nitrate ions.
Arrhenius Acids Examples
Hydrochloric acid (HCl)
Nitric acid (HNO3)
Sulphuric acid (H2SO4)
Phosphoric acid (H3PO4)
Carbonic acid (H2CO3)
Acetic acid (CH3COOH)
Arrhenius Base
An Arrhenius base is a substrate that increases the concentration of hydroxide ions in the aqueous solution. The example for Arrhenius base is highly soluble sodium hydroxide compound in water, which dissociates to give sodium ion and hydroxide ion.
In aqueous solution, NaOH completely dissolves to give hydroxide ion and sodium ion, to increase the concentration of hydroxide ions.
NaOH(aq) → Na+(aq) + OH–(aq)
Some other examples of Arrhenius base are 1st and 2nd group hydroxides, like LiOH and Ba(OH)2.
Arrhenius Base Examples
Sodium hydroxide NaOH
Potassium hydroxide KOH
Calcium hydroxide Ca(OH)2
Magnesium hydroxide Mg(OH)2
Limitations of Arrhenius theory
The Arrhenius theory is applicable only in aqueous solution; for example, according to the theory, HCl is an acid in the aqueous solution but not in benzene, even though it donates H+ ion to the benzene. Also, under Arrhenius’s definition, the solution of sodium amide in liquid ammonia is not alkaline, even though amide ion deprotonates the ammonia.
Summary
According to Arrhenius’s theory of acid-base, acids are those which readily dissociate to give the hydrogen ions in aqueous solution.
Alkaline species dissolve in aqueous solution to give hydroxide ions.