At a certain temperature the vapor pressure of pure acetyl bromide is measured to be . Suppose a solution is prepared by mixing of acetyl bromide and of heptane . Calculate the partial pressure of acetyl bromide vapor above this solution. Round your answer to significant digits. Note for advanced students: you may assume the solution is ideal.

0.17 atm

Explanation:

Raoult´s law can be applied in solving this problem:

Pa= XaPºa   (a= acetyl bromide in this case)

where Pa = partial pressure acetyl bromide

         Xa = mole fraction of acetyl bromide in the solution

          Pºa=  vapor pressure of pure acetyl bromide = 0.75 atm(given)

Hence we can find the mole fraction of the acetone in the mixture:

Let the number of moles of acetone be a and the number of moles of thiophene be t

Xa = mol of a / ( mol of a + mol of t )        

We now have;

Molar Weight of  a= 112.95 g/mol  

number of moles of a = 51.8 g/mol x 1 mol/122.95 g  =  0.42 moles

Molar Weight of t = 84.14 g/mol  

number of moles of  t = 123 g x  1mol/84.14 g= 1.46 mol

mole fraction of a; Xa = 0.42/ (0.42 + 1.46) = 0.22

Pa = 0.22 x 0.75 atm = 0.17 atm