- #1

skaai

- 16

- 0

consider this simple problem: 193 mL or O

_{2}was collected over water with pressure = 762 mmHg at 23°C. How many grams of oxygen were collected?

The strategy is simple enough: P

_{T}= P

_{o2}+ P

_{water}

P

_{oxygen}= 741 mmHg →n=[itex]\frac{pV}{RT}[/itex]=7.69x10

^{-4}mol = 2.46 x 10

^{-2}g (see example in full)

but every time I look at that answer, I ask myself,

**what about the O**

_{2}dissolved in the water?- granted, the question gives you an easy out by NOT asking for the total O
_{2}, but just the O_{2}collected, but assume I want to know the total O_{2}evolved... which in reality I__need to know__if I want to calculate the stoichiometry of a decomposition (such as KClO_{2}that produces O_{2}.

the textbooks tell me to ignore it with gasses that do not dissolve appreciably in water, but then many such books (like the one in the link) ask you to calculate the O

_{2}evolved... suggesting O

_{2}does not dissolve appreciably in water...

but,

Fick's Law and Henry's Law both tell me a significant amount of the gas WILL dissolve in the water, and if I'm not counting it, then I'm going to be off by that amount, right? I mean, we rely on Fick's law to calculate oxygen diffusion across the alveoli of the lungs!

so why don't the Dalton's "gas over water" examples include the amount of oxygen in the water? (another example of this). I almost thought I had this when I assumed the P

_{O2(gas)}= P

_{O2(liquid)}but this would suggest I add a third term to the above equation, right/wrong?

won't ignoring the dissolved gas in the water produce an underestimate?

(remember the book accepts O2 as being minimally soluble but Fick and Henry both say it is)...

I'd be happy to do the math, but I don't know where to start to prove this to myself, as the above equation seems incomplete, or I'm missing something.

thanks so much for considering my dilemma!