Acid and Base Theory

1) Arrhenius Concept of (Acid and Base Theory)

• Acids: Substances that dissociate in water to produce hydrogen ions (H⁺).

• Bases: Substances that dissociate in water to produce hydroxide ions (OH⁻).

Example

• Acid: HCl(aq) → H⁺(aq) + Cl⁻(aq)

• Base: NaOH(aq) → Na⁺(aq) + OH⁻(aq)

• Neutralization reaction: HCl(aq) + NaOH(aq) → H₂O(l) + NaCl(aq)

Limitations

• Only applies to aqueous solutions.

• Does not explain non-aqueous or gas-phase reactions.

• Cannot account for substances without H⁺ or OH⁻ ions.

2) Bronsted-Lowry Concept

• Acids: Proton (H⁺) donors.

• Bases: Proton (H⁺) acceptors.

Example

• Acid: H₂O(l) + NH₃(aq) ⇌ OH⁻(aq) + NH₄⁺(aq)

• Base: NH₃(aq) + H₂O(l) ⇌ NH₄⁺(aq) + OH⁻(aq)

• Conjugate acid-base pairs: NH₄⁺/NH₃ and H₂O/OH⁻

Advantages

• Applicable to both aqueous and non-aqueous solutions.

• Explains acidic or basic behavior of substances without H⁺ or OH⁻ ions.

Limitations

• It does not explain the acid-base behavior of substances that do not involve proton transfer.

• It does not account for reactions where electron pairs play a significant role.

3) Lewis Concept

• Acids: Electron-pair acceptors.

• Bases: Electron-pair donors

Example

• Lewi's acid: BF₃ + F⁻ → BF₄⁻

• Lewi's base: F⁻ + BF₃ → BF₄⁻

Advantages

• Applies to a wide range of reactions, including non-proton-transfer processes.

• Covers reactions in all phases (gas, liquid, solid) and solvents.

Limitations

• Can be too broad, classifying non-traditional acids/bases.

• More abstract and less intuitive than other concepts of Acid and Base Theory