Respuesta :
Answer: The vapor pressure of methanol solution at 298K is 107.12 torr
Explanation:
As the relative lowering of vapor pressure is directly proportional to the amount of dissolved solute.
The formula for relative lowering of vapor pressure will be,
[tex]\frac{p^o-p_s}{p^o}=i\times x_2[/tex]
where,
[tex]\frac{p^o-p_s}{p^o}[/tex]= relative lowering in vapor pressure
i = Van'T Hoff factor = 1 (for non electrolytes)
[tex]x_2[/tex] = mole fraction of solute =[tex]\frac{\text {moles of solute}}{\text {total moles}}[/tex]
Given : 38.5 g of urea is present in 142 g of methanol
moles of solute (urea) = [tex]\frac{\text{Given mass}}{\text {Molar mass}}=\frac{38.5g}{60g/mol}=0.64moles[/tex]
moles of solvent (methanol) = [tex]\frac{\text{Given mass}}{\text {Molar mass}}=\frac{142g}{32g/mol}=4.4moles[/tex]
Total moles = moles of solute + moles of solvent = 0.64 + 4.4 = 5.04
[tex]x_2[/tex] = mole fraction of solute =[tex]\frac{0.64}{5.04}=0.127[/tex]
[tex]\frac{122.7-p_s}{122.7}=1\times 0.127[/tex]
[tex]p_s=107.12torr[/tex]
Thus the vapor pressure of methanol solution at 298K is 107.12 torr
