What is molar concentration of weak monobasic acid if dissociation constant is \(5 \times 10^{-8}\) and undergoes \(0.5 \%\) dissociation?

\(\begin{aligned} & \text { Weak monobasic acid } \longrightarrow \mathrm{HA} \\ & \mathrm{t}=0, \mathrm{CA} \\ & \mathrm{t}, \mathrm{C}-\mathrm{cx} \\ & \text { Dissociation Constant }(\mathrm{K})=\frac{\left[\mathrm{H}^{+}\right]\left[\mathrm{A}^{-}\right]}{[\mathrm{HA}]}+\mathrm{A}_{\mathrm{aq}}^{-} \\ & =\frac{\mathrm{cx} \cdot \mathrm{cx}}{\mathrm{c}-\mathrm{cx}} \\ & \mathrm{K}=\frac{\mathrm{cx}}{1-\mathrm{x}} \\ & \mathrm{x}=0.5 \% \text { or } 0.005=5 \times 10^{-3} \\ & \text { So } 1-\mathrm{x} \simeq 1 \\ & \mathrm{~K}=\mathrm{cx} \\ & \mathrm{C}=\frac{\mathrm{k}}{\mathrm{x}^2}=\frac{5 \times 10^{-8}}{\left(5 \times 10^{-3}\right)^2}=\frac{10^{-2}}{5} \\ & =0.002 \mathrm{M}\end{aligned}\)