${\mathrm{H}}_2\mathrm{S}$ a toxic gas with rotten egg like smell is used for the qualitative analysis, if the solubility of ${\mathrm{H}}_2\mathrm{S}$ in water, at STP is 0.195 mole.${\mathrm{kg}}^{-1}$ the Henry's law constant is

Henry's law relates the pressure of a gas in equilibrium with its solubility in a liquid. The formula is:

$\mathrm{P}={\mathrm{K}}_{\mathrm{H}}.\mathrm{X}$

Solubility = 0.195 moles/Kg of ${\mathrm{H}}_2\mathrm{S}$

No. of mole of ${\mathrm{H}}_2\mathrm{O}=\frac{1000}{18}=55.5$

$\mathrm{X}=\frac{0.195}{55.5}=0.003$

$\mathrm{P}={\mathrm{K}}_{\mathrm{H}}.\mathrm{X}$

1atm =${\mathrm{K}}_{\mathrm{H}}.0.003$

${\mathrm{K}}_{\mathrm{H}}=\frac{1}{0.003}=285.6 \mathrm{bar}$