A 0.21 m3 (55 gal) drum contains 100 L of a mixture of several degreasing solvents in water. The concentration of trichloroethylene in the headspace (gas phase) above the water was measured to be 0.00301 atm. The Henry's constant for trichloroethylene is 0.00985 atm·m3·mol-1 at 25°C. What is the concentration of trichloro-ethylene in the water in units of molarity? (Assume that the temperature of the solution is 25°C.)

0,0003 M

Explanation:

Henry's Law states that the solubility of a gas in a liquid is proportional to the pressure of the gas over the solution. It's equation can be written as:

KC = P

where:

K: Henry's constant at a given temperature [atm. L/mol] C: molarity of the gas in the liquid phase [mol/L] P: pressure of the gas in the gas phase [atm]

To solve the problem, we replace the data in Henry's Law equation using the appropiate units.

1) Changing our data to appropiate units:

K = 0,00985 atm. m3/mol * (1000 L/1 m3) = 9,85 atm. L/mol

P = 0,00301 atm/1 atm = 0,00301

2) Clearing the incognita:

KC=P ... C=P/K

3) Replacing our values:

C=0,00301 atm/9,85 atm. L/mol = 0.0003 mol/L = 0,0003 M

4) Answer:

The concentration of trichloro-ethylene in the water is 0,0003 M