The solubility of nitrogen gas at 25 degrees C and 1 atm is 6.8 x 10^ (-4) mol/L. If the partial pressure of nitrogen gas in air is 0.76 atm, what is the concentration (molarity) of dissolved nitrogen?

5.2 x 10^ (-4) M

1.1 x 10^ (-5) M

4.9 x 10^ (-4) M

3.8 x 10^ (-4) M

6.8 x 10^ (-4) M

5.2 x 10⁻⁴ M.

Explanation:

The relationship between gas pressure and the concentration of dissolved gas is given by Henry's law:

P = kC

where P is the partial pressure of the gaseous solute above the solution.

k is a constant (Henry's constant).

C is the concentration of the dissolved gas.

At two different pressures, there is two different concentrations of dissolved gases and is expressed in a relation as:

P₁C₂ = P₂C₁,

P₁ = 1.0 atm, C₁ = 6.8 x 10⁻⁴ mol/L.

P₂ = 0.76 atm, C₂ = ? mol/L.

∴ C₂ = (P₂C₁) / P₁ = (0.76 atm) (6.8 x 10⁻⁴ mol/L) / (1.0 atm) = 5.168 x 10⁻⁴ mol/L ≅ 5.2 x 10⁻⁴ M.