[Fish200398]

the solubility of oxygen in 1 lt water 25 c 1 atm is 28 ml. How much Lt O2 can be dissolve in 1 lt water 25 c 4 atm?

I though using PV=nRT which gives me PV=P2V2, V2 = 7ml.
I dont understand Henry Law...

[Borek]

You can't use some randomly selected law to solve a problem that is described by another one. It won't ever work. But you are right mentioning Henry's Law, that's the one that should be used here.

Can you write the Henry's law? What does it say?

[Fish200398]

Theres so many equations https://en.m.wikipedia.org/wiki/Henry%27s_law

[Borek]

Sadly, wikipedia article is poorly written, no wonder you feel lost.

See if this formulation won't be better.

[Fish200398]

C = k.P
C = Molarity
k = Henrys Law
P = Pressure

So, how i should find C?

[Borek]

the solubility of oxygen in 1 lt water 25 c 1 atm is 28 ml

You know how much oxygen dissolved and in what volume.

[Fish200398]

Ok. So, the molarity is n/volume

While the mole of oxygen using pv/RT=n ? = 28/(0.082 * 298) = n ?

[Borek]

Close, but watch your units.

[Fish200398]

0.028/(0.082 * 298) = mole

Then i get C


 should i find k? Or P ?

[Borek]

Pressure is given, find k, then calculating amount of oxygen dissolved at any other pressure will be trivial.

[Fish200398]

Ok thanks

[Borek]

Note: there are many ways to skin that cat. Actually once you understand the Henry's law and direct proportionality the answer is immediately obvious. I preferred to show you the most sure way, which may be not the fastest, but is guaranteed to yield a correct result.

[Fish200398]

What is that?

[Borek]

One of possible formulations of Henry's law is that no matter what the pressure is, the volume of the gas that dissolves in a given volume of liquid is always the same.

[Enthalpy]

the solubility of oxygen in 1 lt water 25 c 1 atm is 28 ml. How much Lt O2 can be dissolve in 1 lt water 25 c 4 atm?

I should like to recommend writing the units properly, too, including capital letters.
Litre is L
Degree celsius is °C
and so on and so forth. It's not only easier to read if you follow the habits, it does also make a difference. Readers understand K as kelvin and k as thousand, M as mega and m as milli. Even without readers, you'll fool yourself if you mix up the symbols.