What Is Arrhenius Theory?

The Arrhenius theory was first introduced by the Swedish scientist Svante Arrhenius in the year 1887. To conduct electricity, one must have free moving ions. Svante Arrhenius noticed that the solution of acid conducts electricity by dissolving the substance in the solution, which dissociates into ions. This concept is well-known these days, but during that time it was controversial. This theory is known as “Electrolytic dissociation.”

Water is a neutral substance, which does not conduct electricity. By dissolving some substance in water, it conducts electricity. These substances are called electrolytes and the process is known as “Electrolytic dissociation.”

Arrhenius Theory of Acid and Base

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.

The general properties of acid and base

Acid Base
Acidic in nature Basic in nature
The concentration of H+ ion is high The concentration of OH ion is high
Taste sour Taste bitter
Are red on blue litmus paper Are blue on red litmus paper
Have PH<7 Have PH>7
Common examples: Lemons, oranges, vinegar, urine, sulfuric acid, hydrochloric acid Common examples: Soap, toothpaste, bleach, cleaning agents, limewater, ammonia, water, sodium hydroxide

Arrhenius acids

Arrhenius Acid

 

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
Hydrochloric acid (HCl)
Nitric acid (HNO3)
Sulfuric 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)

Arrhenius Base

Some other examples of Arrhenius base are 1st and 2nd group hydroxides, like LiOH and Ba(OH)2.

LiOH(s)H2OLi+(aq)+OH(aq)LiOH(s)\overset{H_{2}O}{\rightarrow}Li^{+}(aq)+OH^{-}(aq)

LIOH(s)

In the above reaction, lithium hydroxide dissolves in water to give lithium-ion and hydroxide ion.

Examples of an Arrhenius base are listed below

Name Formula
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.