Chemistry - Ionic Equilibrium Question with Solution | TestHub

For weak organic acid indicators

$\text{pH}={\text{pK}}_{\text{In}}+\text{log}\frac{\left[{\text{In}}^{-}\right]}{\left[\text{HIn}\right]}$

$\text{4}\text{.3}={\text{pK}}_{\text{In}}+\text{log 7}$

${\text{pK}}_{\text{In}}=4.3-0.845=3.455$

${\text{pK}}_{\text{In}}=-{\text{log}}_{\text{10}}{\text{K}}_{\text{In}}$

${\text{K}}_{\text{In}}=\text{Antilog}\left(-{\text{pK}}_{\text{In}}\right)$

${\text{K}}_{\text{In}}=\text{Antilog}\left(-3.455\right)$

$=3.5\times {10}^{-4}$