Calculating pressure in sparkling wine

[Ramino]

I need to calculate bars of pressure of a sparkling wine containing 3.92 gram of CO2 per liter in a sealed container at standard temperature and pressure. Please help...

[hermanntrude]

are you given a Kp? or a vapor pressure for CO2?

 

it's not the pressure of the wine you're after, but the pressure of the CO2 over the wine. at least that's what i expect. it's hard to pressurise liquids very much.

[Ramino]

vapor pressure for CO2 at 0 °C should be 26172.964 mmHg or 506.185 PSI.

 

you're right. I need the pressure of CO2 over the wine. As you can tell I am confused...

 

One more thing that may or may not be relevant: Molar Mass of CO2 is 44 g/mol

[insane_alien]

it's not the pressure of the wine you're after, but the pressure of the CO2 over the wine. at least that's what i expect. it's hard to pressurise liquids very much.

 

the liquid will be at the same pressure as the gas above it(well, hydrostatic pressure will result in a higher pressure below the surface but you get the idea).

 

i suspect you were thinking of compression rather than pressure there.

 

you need the equilibrium constant for CO2 solubility.

[hermanntrude]

the liquid will be at the same pressure as the gas above it(well, hydrostatic pressure will result in a higher pressure below the surface but you get the idea).

 

i suspect you were thinking of compression rather than pressure there.

 

you need the equilibrium constant for CO2 solubility.

 

I meant what I said. it's hard to pressurise a liquid, which makes speaking of its "pressure" usually pointless, since, as you so rightly said, it's most likely going to be the same as the atmospheric pressure or pressure above it.

 

And yes, we need the Kc to be able to do this problem

[insane_alien]

no, you still don't get it. you can pressurize a liquid very easily. if i have water sitting in a piston and i place a load on it, i will increase the pressure of the liquid.

 

the liquid will not COMPRESS very much(not even a visible amount usually) but the pressure would rise the same amount as if it were a gas.

[hermanntrude]

no, you still don't get it. you can pressurize a liquid very easily. if i have water sitting in a piston and i place a load on it, i will increase the pressure of the liquid.

 

the liquid will not COMPRESS very much(not even a visible amount usually) but the pressure would rise the same amount as if it were a gas.

 

OK point taken. But Boyle's law doesnt apply.

[insane_alien]

neither does the DMCA for the same reason.

 

its completely unrelated to the thing under discussion. boyles law deals with ideal gases. the champagne is neither a gas nor ideal.

[hermanntrude]

to be fair, though, the question is about the pressure of CO2 above the champagne, so it IS about a gas and one which is fairly close to ideal.

[John Cuthber]

My word, what a lot of things the original post isn't about . Anyway, this might help

http://en.wikipedia.org/wiki/Henry%27s_law

[CaptainPanic]

Shouldn't you also know the pH of the wine in case of CO2 solubility??

 

When CO2 dissolves into water, it forms a (weak) acid:

CO2 + H2O --> H2CO3

 

This weak acid can then dissociate to bicarbonate:

H2CO3 --> H+ + HCO3-

or even carbonate:

H2CO3 --> 2 H+ + CO3(2-)

 

If the pH is high (a basic solution), almost all the H2CO3 will dissociate and form a carbonate. This means that all CO2 reacts away. This then means that more CO2 can dissolve.

 

The opposite is also true: if you add an acid to a carbonate solution, it will form bubbles of CO2. (The partial pressure of CO2 increases, but you don't need to add any CO2 to the system... it was there already).

 

Calculating the equilibrium at a certain pH is a bit of a pain in the butt. It's a system with three equilibrium equations (for the two reactions and the dissolving of the CO2). You'll need the acid/base constants of the two acid/base reactions (to carbonate and bicarbonate) and Henry's constant for CO2.

 

But, let us assume for now that the 3.92 g/l is actual CO2, and not (bi)carbonate. If all what I just explained has been solved already, and we know that (bi)carbonates are not in the 3.92 g/l. Then the use of Henry's law (see: previous post) is correct.

[John Cuthber]

I doubt that (m)any wines are basic enough for significant bicarbonate to be present.