$HA ⇌  H^+ + A^-$   $K$=$\frac{{\left[ {{H^{_ + }}} \right]\,\,\,\left[ {{A^ – }} \right]}}{{\left[ {HA} \right]}}$

નિર્બળ એસિડનું પ્રબળ બેઇઝ વડે તટસ્થીકરણ કરતાં, $HA  +  OH^-  ⇌ A^-  +  H_2O$

તો $\,{\text{K}}\,\, = \,\,\,\frac{{\left[ {{{\text{A}}^{\text{ – }}}} \right]}}{{\left[ {HA} \right]\,\,\,\,\left[ {O{H^ – }} \right]}}\,\,\,………\,\,(ii)$

$(i)$ ને $(ii)$ વડે ભાગતા,$\,\frac{{{{\text{K}}_{\text{a}}}}}{{\text{K}}}\,\, = \,\,\left[ {{H^ + }} \right]\,\left[ {O{H^ – }} \right]\,\, = \,\,{K_w}\,\,\,\,\,\,\,\therefore \,\,K\,\, = \,\,\frac{{{K_a}}}{{{K_w}}}\,\, = \,\,\frac{{{{10}^{ – 5}}}}{{{{10}^{ – 14}}}}\,\, = \,\,{10^9}$