Question

Which of the following symbol represents acid dissociation constant?

• A. $pH$
• B. $pOH$
• C. $K_a$
• D. $K_b$
• E. $K_w$

Answer 1

The correct option is C $K_a$

An acid dissociation constant, $K_a$, (also known as acidity constant, or acid-ionization constant) is a quantitative measure of the strength of an acid in solution. It is the equilibrium constant for a chemical reaction known as dissociation in the context of acid–base reactions. In aqueous solution, the equilibrium of acid dissociation can be written symbolically as:


where $HA$ is a generic acid that dissociates into $A-$, known as the conjugate base of the acid and a hydrogen ion which combines with a water molecule to make an hydronium ion. In the example shown in the figure, $HA$ represents acetic acid, and $A-$ represents the acetate ion, the conjugate base.
The chemical species $HA,A^{-}$ and $H_3{O}^{+}$ are said to be in equilibrium when their concentrations do not change with the passing of time. The dissociation constant is usually written as a quotient of the equilibrium concentrations (in mol/L), denoted by $\left[HA\right],[A-]$ and $\left[H_3{O}^{+}\right]$