Question

Hydrogen sulfide, H₂S, is a gas that is responsible for the odor of rotten eggs. The solubility of H₂S_(g) in water at STP is 0.195 M. What is the solubility of H₂S_(g) in units of M in water at 0°C and a partial pressure of 0.155 atm?

What is the vapor pressure in mmHg of a solution made by dissolving 12.5 g of NaCl in 500.0 g of water at 70°C, assuming a van't Hoff factor of 1.9? The vapor pressure of pure water at 70°C is 233.7 mmHg.

Answer 1

Henry's law relates that there is a direct ratio beteen molarity of a gas & the pressure upon it.

Henry's Law Constant of H2S at 0 degrees C is 0.195 mol/L*atm

molarity = (k) (pressure)

molarity = (0.195 mol/L*atm) (0.155 atm)

molarity = 0.030225 atm

(b)

Vapor pressure of a solution = (mole fraction of the solvent) x (vapor pressure of the solvent)

(500.0 g x 1mole) / 18.02g = 27.75 moles water.
(12.5 g x 1mole) / 58.5 g = 0.21moles NaCl 0.21 moles Na+ and 0.21 moles Cl-.

Total moles = 27.75 + 0.21 + 0.21 = 28.17 moles

Mole fraction water = 27.75 / 28.17 = 0.985

vapor pressure = 233.7 mmHg x 0.985 = 230.2 mmHg.