Question

At a certain temperature the vapor pressure of pure thiophene (CHS) is measured to be 82. torr, Suppose a solution is prepared by micing 88.8 g of thiophene and 77.5 g of benzene (CH). Calculate the partial pressure of thiophene vapor above this solution. Round your answer to 2 significant digits. Note for advanced students you may assume the solution is ideal X $ 2

Answer 1

Molar mass of C4H4S,

MM = 4*MM(C) + 4*MM(H) + 1*MM(S)

= 4*12.01 + 4*1.008 + 1*32.07

= 84.142 g/mol

Molar mass of C6H6,

MM = 6*MM(C) + 6*MM(H)

= 6*12.01 + 6*1.008

= 78.108 g/mol

n(C4H4S) = mass/molar mass

= 88.8/84.142

= 1.055

n(C6H6) = mass/molar mass

= 77.5/78.108

= 0.9922

n(C4H4S),n1 = 1.055 mol

n(C6H6),n2 = 0.9922 mol

Total number of mol = n1+n2

= 1.055 + 0.9922

= 2.048 mol

use:

Mole fraction of C4H4S:

X(C4H4S) = n1/total mol

= 1.055/2.048

= 0.5154

According to Raoult’s law:

P = Po*X(solvent)

p = 82.0*0.5154

p = 42.3 torr

Answer: 42 torr