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Vapour pressure of pure water at 25 celsius is 80 torr and that of an aqueous solution os 75 torr

Simon , 3 Years ago
Grade 12
anser 1 Answers
Anish

Last Activity: 3 Years ago

Let M be the molecular weight of solute.
 
Number of moles of solute = 
M
5.40
 
 
Number of moles of water = 
18
90.0
 =5
 
Mole fraction of solute = 
M
5.40
 +5
M
5.40
 
 = 
5.40+5M
5.40
 
 
Relative lowering in the vapour pressure = 
0
 
0
 −P
 = 
23.76
23.76−23.32
 =0.01852
 
The relative lowering in the vapour pressure of the solution is equal to the mole fraction of solute. 
 
0.01852= 
5.40+5M
5.40
 
 
⟹5.40+5M=291.6
 
5M=286.2
 
⟹M=57.24 g/mol

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