HX ⇌ H+ + X- is given by the equation:

$$Ka = \frac{[H^+][X^-]}{[HX]}$$

where [H+], [X-], and [HX] represent the equilibrium concentrations of hydrogen ions (H+), conjugate base (X-), and the undissociated acid (HX), respectively. Ka is a quantitative measure of the strength of an acid in solution, indicating its tendency to donate a proton (H+ ion).

This equation defines the Ka for a monoprotic acid, which is an acid that can donate a single proton. For polyprotic acids (acids that can donate multiple protons), there will be multiple Ka values, each corresponding to the dissociation of a specific proton.

The value of Ka provides information about the acidity of the solution:

- A large Ka value indicates that the acid dissociates more completely, resulting in a higher concentration of H+ ions and a lower pH.

- A small Ka value indicates that the acid dissociates less completely, leading to a lower concentration of H+ ions and a higher pH.

The Ka value is a characteristic property of a given acid and is temperature-dependent. It is commonly used in acid-base chemistry to quantify the strength of acids, predict the extent of dissociation, and perform various calculations related to acid-base equilibria.