general chem question

[dl9006]

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could someone help me w this question?

At 90 degrees celcius, benzene has a vapor press= 1022torr and toluene has vapor pressure= 406 torr.

Given this info, what is the composition of the benzene-toluene solution that will boil at 1 atm pressure and 90 degrees celcius, assuming that the solution is ideal.

ANS: The mole fraction of benzene is 0.574


how do we get this ans?

thanks

 

[chessxwizard]

The partial pressures of each component in a solution are additive when solving the total pressure:

x = mole fraction of benzene
y = mole fraction of toluene

System of equations:
1) x + y = 1
(the mole fractions of the mixture, when added, will be 100%)
2) 760 = 1022x + 406y
(the pressure exerted by each gas, when added, will be the atmospheric pressure at boiling point)

Solve!
x = 1-y

760 = 1022(1-y) + 406y
760 = 1022-1022y+406y
-616y=-262
y=.425

y is the mole fraction of toluene, but you want the mole fraction of benzene!

x+y=1
x+.425=1
x = 1-.425 = .575, which is your answer!

 

[dl9006]

ohh i see

thanks for you help!

 

[supraman]

my test is in 5 days, is this the level i can expect on the DAT? I really doubt it lol

 

[dl9006]

are you sure about that?

how hard is the chem section?

i been looking at the dat destroyer and some other random study guides

but im not too sure the lvl of difficulty to expect.


i hope most of it is easy

 

[Sea of ASH]

The partial pressures of each component in a solution are additive when solving the total pressure:

x = mole fraction of benzene
y = mole fraction of toluene

System of equations:
1) x + y = 1
(the mole fractions of the mixture, when added, will be 100%)
2) 760 = 1022x + 406y
(the pressure exerted by each gas, when added, will be the atmospheric pressure at boiling point)

Solve!
x = 1-y

760 = 1022(1-y) + 406y
760 = 1022-1022y+406y
-616y=-262
y=.425

y is the mole fraction of toluene, but you want the mole fraction of benzene!

x+y=1
x+.425=1
x = 1-.425 = .575, which is your answer!

u better not get lower than at 27 on your QR man! 👍