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osmotic gradient.

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osmotic gradient.

Postby student12 » Thu May 25, 2006 8:04 am

I have a query wether or not insoluble molecules (eg:starch) within a solution will alter the osmotic gradient?
or does this only apply for soluble molecules?(eg:glucose)

Plz expain. Thank you.
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Postby MrMistery » Thu May 25, 2006 5:56 pm

ok, so you can look at osmosis as simple(and facilitated!) diffusion of free water through the membrane down it's concentration gradient. Free water meaning the water that is not bounded by a molecule by any kinds of bonds(more molecules, higher concentration=>more bound water and a lower concentration of free water). Since insoluble molecules do not form intermolecular bonds with water they do not directly affect the diffusion of water across a membrane
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Postby Ultrashogun » Thu May 25, 2006 6:18 pm

The above poster is correct, but another thing you might want to look at is the formula for osmotic pressure:

pi = C R T

The C stands for concentration of the solution and since unsolved substance makes an emulsion or suspension those moles do nothing towards the osmotic pressure.
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Postby MrMistery » Fri May 26, 2006 5:30 pm

@Ultrashogun

Don't do that! Never do that. That's what my teachers do and i'm never happy with it. Don't throw a formula like with a slingshot. If you are going to give someone a formula, explain how it was obtained, for them to actually understand. Although my post was a little explanation, it can't by far explain your formula.
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Postby Ultrashogun » Fri May 26, 2006 7:48 pm

Well sorry, but the point was never the formula, but what aspects the osmotic pressure depends on.

The formula is obtained from the general gas law:

P V = n R T --> P = pressure, V = Volume, n = number of mols, R = gas constant , T = absolute temperature

divide by V to obtain:

P = n R T / V

we know from the formula for molarity that C = n / V, so:

P = C R T, we then call this pressure "pi".

You can get the general gas law from the laws of Gay-Lussac and Boyle.
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Postby MrMistery » Sat May 27, 2006 11:05 am

That's much better. You are on your way to becoming a good teacher :)
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Postby 2810712 » Sat May 27, 2006 11:52 am

Hey people kinetic theory of gases neglects any intermolecular forces! so you can't relate bound water' to it that way. Many times i hate it when teachers neglect this assumption of kinetic theory of gases. Also, without considering intermolecular forces u can't explain [ not prove] how is Cp>Cv on the molecular level.
From Atkins Phy Chem. first law of thermodynamics neglects intermolecular forces as the Kinetic theory of gases does. & then we apply the energy conservation!
So, the text-book thermodynamics is like most text-chapters immpractical!
See intermolecular forces ain't that negligible always. Also in the equation deltaE=q-delta(n)RT , we take T constant but still we don't take delta E as zero! This can only be explained by the intermolecular forces...

Do you think the same..?

Ved
Last edited by 2810712 on Sat May 27, 2006 3:41 pm, edited 1 time in total.
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Postby Ultrashogun » Sat May 27, 2006 11:59 am

2810712 wrote:Hey people kinetic theory of gases neglects any intermolecular forces! so you can't relate bound water' to it that way. Many times i hate it when teachers neglect this postulate of kinetic theory of gases. Also, without considering intermolecular forces u can't explain [ not prove] how is Cp>Cv on the molecular level.
From Atkins Phy Chem. first law of thermodynamics neglects intermolecular forces as the Kinetic theory of gases does. & then we apply the energy conservation!
So, the text-book thermodynamics is like most text-chapters immpractical!
See intermolecular forces ain't that negligible always. Also in the equation deltaE=q-delta(n)RT , we take T constant but still we don't take delta E as zero! This can only be explained by the intermolecular forces...

Do you think the same..?

Ved


Im sorry but I just dont see the relevance for this.
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Postby 2810712 » Sat May 27, 2006 3:09 pm

apologise friends...that was a little off-topic,
] but as u quoted the formula PV=nRT, which is also derived with the help of kinetic theory of gases i just put my thoughts about it, sorry, still i want ur views about the previous post...
sorry...
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