For a generic weak acid equilibrium, there is a Ka. Which option is Ka?

For a generic weak acid equilibrium, there is a Ka. Which option is Ka?

• A. Kb
• B. Kw
• C. Ka
• D. pH

Answer: (C)

Ka is the acid dissociation constant for a weak acid in water. It quantifies how far HA dissociates: HA ⇌ H+ + A−, with Ka = [H+][A−]/[HA]. A larger Ka means more ionization and a stronger acid, while a smaller Ka means less ionization and a weaker acid. The other terms don’t describe the acid’s equilibrium constant: Kb is the base dissociation constant, Kw is the autoionization constant of water, and pH is a measure of hydrogen ion concentration, not an equilibrium constant. So, the value characterizing a weak acid’s equilibrium is Ka.

Ka is the acid dissociation constant for a weak acid in water. It quantifies how far HA dissociates: HA ⇌ H+ + A−, with Ka = [H+][A−]/[HA]. A larger Ka means more ionization and a stronger acid, while a smaller Ka means less ionization and a weaker acid. The other terms don’t describe the acid’s equilibrium constant: Kb is the base dissociation constant, Kw is the autoionization constant of water, and pH is a measure of hydrogen ion concentration, not an equilibrium constant. So, the value characterizing a weak acid’s equilibrium is Ka.