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

Question

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

Aicharya · Accepted Answer

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

What is molar concentration of weak monobasic acid if dissociation constant is $5 \times 10^{-8}$ and…

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