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Physical Chemistry

Scorching goIITian

Joined:	6 Apr 2008
Post:	236

10 Apr 2008 12:30:08 IST

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Solublity problem

None

At 20⁰ C the vapour pressure of ether is 442 mm of Hg.When 6.1 g of a substance is dissolved in 50g of ether (mol. wt.=74) ,the vapour pressure falls to 410mm .Calculate the molecular weight of the substance?

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chemicaltester

Scorching goIITian

Joined: 12 Mar 2008

Posts: 233

10 Apr 2008 13:23:23 IST

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see initial vapour pressure be Po
final presure be P
so relative change is Po -P/Po
we know that it is equal to mole fraction of solute
so Po - p/Po =X2
now X2 =no of moles of solute/total no of moles in solution
no of moles solute =W2/M2
also total no of moles in solution is W2/M2 + W1/M1
so equation becomes
Po -P/Po = ( W2 / M2 ) / (W2 /M2 +w1 +M1)
Po is given
P is given
W2 is given

W1 is given also M1 is given
so using above equation find M2

rate me if u understan or nudge me if i m wrong

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