$H_2S$,a toxic gas with rotten egg like smell,is used for the qualitative analysis. If the solubility of $H_2S$ in water at $STP$ is $0.195 \, m$,calculate Henry's law constant.

(N/A) Given,molality $(m) = 0.195 \, mol \, kg^{-1}$.
This means $0.195 \, mol$ of $H_2S$ is dissolved in $1000 \, g$ $(1 \, kg)$ of water.
Moles of water $= \frac{1000 \, g}{18 \, g \, mol^{-1}} = 55.56 \, mol$.
Mole fraction of $H_2S$ $(x) = \frac{n_{H_2S}}{n_{H_2S} + n_{H_2O}} = \frac{0.195}{0.195 + 55.56} = \frac{0.195}{55.755} \approx 0.0035$.
At $STP$,pressure $(p) = 0.987 \, bar$.
According to Henry's law,$p = K_H \cdot x$.
$K_H = \frac{p}{x} = \frac{0.987 \, bar}{0.0035} \approx 282 \, bar$.