Q.Define the degree of ionization $\alpha$ of a weak electrolyte, and state why $\alpha$ for a strong electrolyte such as $\text{HCl}$ is taken to be effectively $1$ in dilute solution.

[!TLDR] $\alpha$ is the fraction of dissolved electrolyte that has ionized; for a strong electrolyte it is essentially 1. [!ANSWER] $\alpha = \dfrac{\text{moles ionized}}{\text{total moles dissolved (initial)}}$; for $\text{HC …

The degree of ionization measures what fraction of the dissolved electrolyte has broken up into ions at equilibrium, out of the total amount originally dissolved — it is a pure (unitless) ratio between 0 and 1, or equivalently a percentage between 0% and 100%. For a weak electrolyte, only a small fraction ionizes, so $\alpha$ is small and, by Ostwald's dilution law, concentration-dependent. $\text{HCl}$, however, is a strong acid: essentially every $\text{HCl}$ molecule dissolved in dilute aqueous solution donates its proton, $\text{HCl} \to \text{H}^+ + \text{Cl}^-$, so the number of moles io …

State the ratio definition of $\alpha$, then reason that a strong electrolyte …

Do not confuse $\alpha \approx 1$ for a strong electrolyte with $K_a$ being large or undefined — strong electrolytes are simply no …