[jj]

I'm trying to solve a problem involving a gas with a H constant of 70.....If sampling a water sample with this gas dissolved in it, is it best to fill a serum bottle and remove headspace, replacing with N2, letting it equilibrate and then sampling for the gas-OR to remove a water sample, placing in another (N2 only) bottle and letting that equilibrate?  Seems as if I would need to know the pressure in the bottles- how is this measured....Only info Ihave is that the gas is SF6 and the H constant is 70.  Question is to calculate how the gas conc in headspace changes in both bottles as the solution ( gas in water) conc changes...Boy I have no idea.  

[Donaldson Tan]

Henry's Law states that the vapour pressure of a component is directly proportional to the mole fraction of the component in a solution, ie.
y_AP = H.x_A.P* where:
y_A is mole fraction of component in gas phase
P: total pressure of gas phase
H: henry's constant
x_A is mole fraction of component in solution phase
P* is saturated vapour pressure of the component

P* can be obtained using the antoine equation:
lg P* = A + B/(C + DT)  where A, B, C. D are constants unique to the substance. and T is the temperature of the system. These values can be looked up in standard data tables.