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Physical Chemistry

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19 Jun 2007 20:35:45 IST

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799

Confusion

None

According to the raoult's law the rel. lowering of vapour pressure is directly proportional to-

a-moles of solvent

b-mole fraction of the solvent

c-i times the mol fraction of solute ,i -->vant hoff's factor

d-none of these

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Himanshu

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19 Jun 2007 20:43:01 IST

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is it c

10904him

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19 Jun 2007 20:48:53 IST

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Actually the answer given to us by our teacher is also c but I am confused that Raoults Law does not state anything about i .It is a matter of vant hoff's correction.
We do not write raoults law in the way as (c).

10904him

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19 Jun 2007 21:09:03 IST

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I would myself prefer answer (d) .

Himanshu

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19 Jun 2007 21:17:20 IST

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c yaar in colligative properties , van't hoff factor comes into play

see v write frmulas as

Poa - Pa / Poa = i*Xb

Pi = i *CRT-----osmotic pressure

del. Tb = i *Kb* molality

del. Tf = i * Kf * molality

so wen the subst. undergoes association or dissociation , we use i

eg. if subst. is CH3COOH which doesnt associate or dissociate , we don't use i

but if it is NaCI or KCI , we use i

hope it helps :) :)

Manasi

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19 Jun 2007 22:08:09 IST

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its "d"

according to raoult's law , the vapour pressure depression takes place when solute is added to a pure solvent..... which is directly proprtional to the no of moles of solute added...

and thats why its called a colligative property....

himanshu isnt wrong... but what u have done is a mathematical calculation... plus vant-hoff factor is a correction, in colligative properties....

10904him

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20 Jun 2007 18:31:03 IST

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Himanshu what you wrote is useless until you try and understand what I am confused with----------One cant change the law like that

Ambareesh Rishi

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20 Jun 2007 18:39:59 IST

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the answer is B because raoults law for non volatile solute states that pressure of solution is equal to pressure of solution =pressure of pure solvent X mole fraction of solvent

Ambareesh Rishi

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20 Jun 2007 18:41:45 IST

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the solutions are taken to be ideal solutions but not sure about the vant hoff factor bcoz its expirementally calculated

10904him

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21 Jun 2007 14:14:49 IST

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What rubbish Anbareesh ......Check out your book

Ambareesh Rishi

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21 Jun 2007 18:39:12 IST

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ooops i am sorry i didnt see the question well .i thought it was vapor pressure.............the relative lowering of vapor pressure of an ideal solution is containing non volatile solute is equal to mole fraction of solute at given temp(this ones is the modified form)..... the original raoults law is"at a given temperature the vapor pressure of solution containing non volatile solute is directly proportional to the mole fraction of the solvent

Himanshu

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21 Jun 2007 18:47:46 IST

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hey y its useless

u dont wanna understand thats ur problrm dude

if u think so , v can't put " i " in any colligative property

1st u try to understand then speak

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