H2S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant.

H2S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant.

Solution

given that

Molality =0.195 m,

Let take mass of solvent (water) = 1 kg 

Use above formula we get

Moles of solute = 0.195 mol

Molar mass of water (H₂O ) = 2 × 1 + 16 = 18 

Mass of water (mass of solvent 1 kg = 1000 g

Number of moles of water = 1000 g / 18 = 55.56 mol

 

Use above formula we get

Mole fraction of H₂S = 0.195/(0.195 + 55.56) = 0.0035

At STP, pressure (p) = 0.987 bar always

According to Henry’s law:

p = K_H × X

K_H  =  p / X   = 0.987 / 0.0035 = 282 bar