Disadvantages of Arrhenius Theory of Acid and Base

Acids and bases are common solutions that can be found everywhere. Apart from water, almost every liquid we encounter in our daily lives has acidic and basic properties. They have entirely different properties and can be neutralised to form H2O. Because they contain dissolved ions, acids and bases in aqueous solutions will conduct electricity. As a result, acids and bases are electrolytes. Strong acids and bases will behave like strong electrolytes and vice versa. This influences the amount of conductivity.

Arrhenius Theory: by Svante August Arrhenius – in 1887

• In 1887, the Swedish scientist Svante Arrhenius proposed the Arrhenius theory for the first time. Free moving ions are required to conduct electricity. Svante Arrhenius discovered that an acid solution conducts electricity by dissolving the substance in the solution, dissociating it into ions.
• This idea is now widely accepted, but it was controversial. “Electrolytic dissociation” is the name given to this theory.
• Water is a non-conducting substance. It conducts electricity by dissolving something in the water.
• The substances in question are known as electrolytes, and the process is known as “Electrolytic dissociation.”
• Acids are substances that dissociate in water to yield electrically charged atoms or molecules, referred to as ions. One of them may be a proton (H+), which bases ions in water to yield hydroxide ions (OH−).
• It is currently believed that the proton cannot exist alone in a water solution; rather, it exists during a combined state with a water molecule because of the hydronium particle (H3O+).
• The hydronium particle continues to be typically noted because of the proton.
• The acidic behaviour of the many well-known acids and the basic properties of well-known hydroxides are explained in their ability to yield H and hydroxide ions.
• Such acids and bases are also classified as robust or weak acids and bases counting on the proton or anion concentration.
• The reaction between associate degree acid and a base results in the formation of salt and water; the latter is the result of the mixture of a proton and an anion.

Arrhenius Acid

An Arrhenius acid is defined as a compound that increases the concentration of H+ ions in water when it is added.

When these H+ ions combine with water molecules, they form the hydronium ion (H3O+). In a chemical equation, this process is shown by adding H2O to the reactants’ side.

HCl(aqueous)→H+(aqueous)+Cl−(aqueous)

Arrhenius Base

An Arrhenius base is defined as a substrate that leads to an increase in the concentration of hydroxide ions in an aqueous solution. The Arrhenius base is a highly soluble sodium hydroxide compound in water that dissociates to give sodium and hydroxide ions.

In an aqueous solution, NaOH dissolves completely to produce hydroxide ions and sodium ions, increasing hydroxide ions’ concentration.

NaOH (aqueous) → Na+(aqueous) + OH–(aqueous)

Limitations of the Arrhenius Theory

• The Arrhenius theory is known for the simplicity with which it provides the classification of acids and bases depending on their strength. But it also possesses a few limitations that can be stated as below: –
• The Arrhenius theory defines acids and bases in terms of their aqueous solutions and not in terms of the substance itself. Thus, it holds true only for aqueous solutions and not gaseous and non-aqueous solutions.
• The Arrhenius theory applies to acids having HA formula and bases having BOH formula. Because of this, it is unable to explain the properties of acids such as CuSO4, AlCl3, CO2, SO2 etc., and the basic properties of Na2CO3, amines, pyridines, NH3 as HA and BOH cannot represent them, respectively.
• Arrhenius could not illustrate why some compounds, despite having basic properties, did not contain hydroxide ions. Metal-Oxides are a common example of this.
• Although calcium carbonate is naturally basic, it lacks OH–.
• Arrhenius could not clarify why some charged sodium compounds, such as zinc chloride, are acidic while others, such as sodium ions, are basic.
• Arrhenius could not describe acid-base reactions that do not occur in water solutions. The reaction between ammonia gas and HCl is an example of an acid-base reaction.
• The theory fails to mention the role a solvent plays in deciding the nature of the acid or base. For example, HCl becomes a strong acid when dissolved in water but a weak acid when dissolved in benzene.

Conclusion

The Arrhenius theory attempts to explain the acidic or basic properties of substances in an aqueous solution. It also helps explain the process of neutralisation and hydrolysis and determine the strength of the acids and bases.