Question
Sun January 30, 2011 By: Doctor Srishty

a solution has 1:4 mole ratio of pentanne to hexane. the vapour pressure of the pure hydrocarbons at 20degree celcious are 440mm of hg for pentane and 120mm of hg for hexane . the mole fraction of pentanne in the vapour phase would be?

Expert Reply
Tue February 22, 2011
Number of moles of pentane = 1
Number of moles of hexane = 4
x pentane = 1/5
x hexane = 4/5
p total = 440 + (120 - 440) * (4/5)
          = 184 mm Hg
p pentane = 1/5 * 440 = 88 mm Hg
p hexane = 4/5 * 120 = 96 mm Hg
 
y pentane = 88 / 184 =0.48 mm Hg
 
y hexane = 96 / 184 =  0.52 mm Hg
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