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

Answer
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Hint: We need to apply Henry’s law in this question which states:
P=kH.x
where p = pressure
x = mole fraction
KH = Henry's constant

Complete Solution :
Given molarity = 0.195m.
Since, Molority=No. of moles of soluteMass of solvent (kg)
Let us assume mass of water = 1kg
So, Moles of solute = Molarity ×Mass of solvent
=0.195 mol
Molar mass of H2S=(2×1)+16=18
No. of moles of water=massmolar mass
=10001855.56 mol
Now, we will find the mole fraction of H2S(x)
=0.1950.195+55.56=0.0035
At STP P=0.987atm
Applying formula in equation (i) we get,
P=kH.x
kH=Px=0.9870.035
kH=282atm

Additional information: -Hydrogen sulfide (orH2S) is a very toxic gas. It has no color but smells like rotten eggs. Excess H2S can halt the breathing centre in the brain which can lead to death. The gas is also known to cause irritation in eyes, nose, lungs and throat.
-Hydrogen sulfide gas occurs naturally in crude petroleum and natural gas. It can be produced by decomposing human and animal waste and is found in sewage treatment plants and livestock areas.

Note: Henry’s law states that- “At a constant temperature, the amount of a gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of the gas in equilibrium with the liquid.” Henry’s constant depends upon the nature of the gas, nature of the solvent, temperature and pressure. This is the reason why different gases have different Henry’s laws constant in different solvents.