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Topic: Work revision concerning the dissolution of gases in liquids  (Read 3156 times)

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Offline Kate

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Work revision concerning the dissolution of gases in liquids
« on: October 27, 2009, 08:36:52 PM »
Hi. I'm having some trouble solving this problem. Can you check my work ?

The solubility of N2 in blood at 37 ºC and at a partial pressure of 0.8 atm is 5.6 x 10 -4 mol/L. A diver breathes compressed air with a partial pressure of N2 of 4 atm. Say the volume of blood in his body is 5 L. Determine the quantity of N2 released in litres when the diver comes back to the surface where the partial pressure of N2 is 0.8 atm.

The solution for this problem is 0.28 dm3. I got a different result.

First, I calculated Henry's constant for N2 at 37 ºC. I got K = 7 x 10 -4 mol dm-3 atm-1. Then, I determined the solubility of N2 at a partial pressure of 4 atm using the value I got earlier for K. The solubility I got was 2,8 x 10 -3 mol/L. After that, I calculated the nº of moles for each solubility. For a solubility of 5.6 x 10 -4 mol/L the nº of moles is 2,8 x 10 -3 mol and for a solubility of 2,8 x 10 -3 the nº of moles is 0,014 mol. Then I subtracted 0,014 mol by 2,8 x 10-3 mol and got 0,0112 mol. Finally, I applied the equation pV = nRT to determine the value of V using 0,8 atm as the value for pressure. I got V = 0,38 dm3???


Offline Borek

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Re: Work revision concerning the dissolution of gases in liquids
« Reply #1 on: October 28, 2009, 04:01:05 AM »
0.0112 is OK, but you should use TOTAL pressure to calculate volume of nitrogen released.
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Offline Kate

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Re: Work revision concerning the dissolution of gases in liquids
« Reply #2 on: October 28, 2009, 04:10:25 AM »
And where do I get the value for total pressure ? Do I use 1 atm ?

Offline Borek

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Re: Work revision concerning the dissolution of gases in liquids
« Reply #3 on: October 28, 2009, 04:20:47 AM »
Yes.

Alternatively, you can calculate total pressure using known composition of air - 78% of nitrogen - and nitrogen partial pressue (0.8 atm) - but first, it gives almost exactly 1 atm, second, it is an overkill.
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Offline Kate

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Re: Work revision concerning the dissolution of gases in liquids
« Reply #4 on: October 28, 2009, 04:23:20 AM »
Oh, ok. Thanks for your help.  :)

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