The vapor pressure of chloroform (CHCl3) is 173 mm Hg at 25 °C. What is the vapor pressure of a solution consisting of 268 g of chloroform and 0.129 mol of a nonvolatile nonelectrolyte?
Given:Vapor pressure of solvent chloroform (CHCl3)p0=173mmHg
Mass of chloroform =268g
Number of moles of non-volatile non-electrolyte solute (n2) =0.129mol
The non-volatile non-electrolyte doesn't contribute to the total vapor pressure of the solution. Thus, the vapor pressure of the solution will be the vapor pressure due to solvent in the solution only i. e.
Vapor pressure of the solution=Vapor pressure of the solvent in the solution
According to Raoult's law, the vapor pressure of any component at a given temperature is equal to the mole fraction of that component in the solution multiplied by the vapor pressure of that component in the pure state.
Thus, vapor pressure of solvent = mole fraction of solvent*vapor pressure of solvent
ps =x1*p0 ... (1)
Here,ps= vapor pressure of solution
x1= mole fraction of the solvent
po =vapor pressure of solvent
For calculating ps, first calculate mole fraction of solvent
Here, n1= number of moles of solvent
n2= number of moles of solute
n1= mass of solvent /molar mass of solvent (chloroform) =268g/119.52g/mol=2.24mol
Molar mass of CHCl3=1* atomic mass of C+1*atomic mass of H+3*atomic mass of Cl
Molar mass =1*12.01g/mol+1*1.01g/mol+3*35.5g/mol
Number of moles of solute =0.129mol
=0.945546644 (unit mol cancelled out)
After round off, x1=0.95
Putting the value of x1 and p0 in equation 1,we get
ps =0.95*173mmHg =164.35mmHg