posted by ieshia
Use Henry's law and the solubilities given below to calculate the total volume of nitrogen and oxygen gas that should bubble out of 1.1L of water upon warming from 25 ∘C to 50 ∘C. Assume that the water is initially saturated with nitrogen and oxygen gas at 25 ∘C and a total pressure of 1.0 atm. Assume that the gas bubbles out at a temperature of 50 ∘C. The solubility of oxygen gas at 50 ∘C is 27.8 mg/L at an oxygen pressure of 1.00 atm. The solubility of nitrogen gas at 50 ∘C is 14.6 mg/L at a nitrogen pressure of 1.00 atm. Assume that the air above the water contains an oxygen partial pressure of 0.21 atm and a nitrogen partial pressure of 0.78 atm.
p = KcC
p = 0.21 when saturated and Kc = about 769 atm*L/mol but you should look this up in your tables and use that number here. Also, I have estimated all of my other answers; you definitely should go through the calculations yourself and refine each of the steps.
C for the sat'd solution at 25C is
about 3E-4M. Convert that to mol.
3E-4 mols/L x 1.1 L = about 3E-4 mols and that x 32 = about 9.5E-3 g which is about 9.5 mg in the 1.1 L @ 25C for O2.
At 50C, oxygen is 27.8 mg/L @ 1atm or
27.8mg/L x 1.1 L = about 30 mg @ 1 atm. If the pressure is to be 0.21 above the solution at equilibrium the solubility will be decreased to about 30 x 0.21 atm/1 atm = about 6.5 mg. So 9.5mg initially - 6.5 mg at 50C is about 3 mg O2 that should bubble out.
N2 can be done the same way, then add the partial pressure of O2 to that of N2 to find total P. Check my thinking.