[pseizure2000]

I know how to use the formula for osmotic pressure (MRT), however the way that this problem incorporates partial pressure into it just confuses the sh*t outta me. Please help me, before I cut my wrists.


The partial pressure of O2 in air at sea level is 0.21 atm. The solubility of O2 in water is 1.38 x 10-3 M at 20°C and Poxygen = 1.00 atm. Calculate the molar concentration of O2 in the surface water of a mountain lake saturated with air at 20°C and an atmospheric pressure of 662.8 torr.

[Borek]

When the total pressure goes down partial pressures go down as well in exactly the same ratio. So if you start with 1 atm of air and 0.21 atm partial pressure of O₂, and then you lower the pressure twice to 0.5 atm total - partial pressure of oxygen goes down to 0.21/2 = 0.105 atm

[pseizure2000]

I think I just realized it's not osmotic pressure but Henry's Law. Yet somehow I still haven't figured out what to do with the 662.8 torr although i think i need to relate it to the partial pressure some way.

[Borek]

You need both. To use Henry's law you need oxygen pressure - and that's what I described in my previous post. Note that the question uses different pressure units, IMHO only to confuse you