Write a balanced equation for the dissociation equilibrium of acetic acid.
The correct answer and explanation is:
Balanced Equation:
CH₃COOH (aq) ⇌ CH₃COO⁻ (aq) + H⁺ (aq)
Explanation (300 words):
The balanced equation above represents the dissociation equilibrium of acetic acid in water. Acetic acid (CH₃COOH) is a weak acid, meaning it does not completely ionize in aqueous solution. Instead, it establishes a reversible equilibrium with its ions. In this equilibrium, one molecule of acetic acid donates a proton (H⁺) to water, resulting in the formation of the acetate ion (CH₃COO⁻) and a hydrogen ion (H⁺), also known as a proton.
Since acetic acid is weak, most of the acid molecules remain undissociated in solution. Only a small fraction splits into ions. This partial dissociation is what defines a weak acid and creates a dynamic equilibrium, meaning the forward and reverse reactions occur at the same rate over time. The double arrow (⇌) in the equation indicates this reversibility.
The extent of dissociation is described by the acid dissociation constant, Ka. For acetic acid, the Ka is approximately 1.8 × 10⁻⁵ at 25°C. This low value supports the fact that acetic acid only ionizes slightly in water.
The equilibrium has practical implications in buffer solutions, titration reactions, and in biological systems. Acetic acid is commonly found in vinegar and is used as an example in acid-base chemistry because its weak nature allows clear study of reversible dissociation. Understanding the dissociation of acetic acid helps in calculating pH, analyzing buffer capacity, and interpreting conductivity of the solution.
In summary, the dissociation of acetic acid in water produces hydrogen ions and acetate ions in a reversible process. The equilibrium highlights the properties of weak acids and helps explain behavior in chemical and biological systems. The balanced equation accurately reflects the conservation of mass and charge in this ionization reaction.