Respuesta :
Answer: The vapor pressure of the solution is 186.4 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 : 21.5 g of lactose is present in 200.0 g of water.
moles of solute (lactose) = [tex]\frac{\text{Given mass}}{\text {Molar mass}}=\frac{21.5g}{342g/mol}=0.0628moles[/tex]
moles of solvent (water) = [tex]\frac{\text{Given mass}}{\text {Molar mass}}=\frac{200.0g}{18g/mol}=11.1moles[/tex]
Total moles = moles of solute (lactose) + moles of solvent (water) = 0.0628+ 11.1 = 11.1628
[tex]x_2[/tex] = mole fraction of solute =[tex]\frac{0.0628}{11.1628}=5.62\times 10^{-3}[/tex]
[tex]\frac{187.5-p_s}{187.5}=1\times 5.62\times 10^{-3}[/tex]
[tex]p_s=186.4[/tex]
Thus the vapor pressure of the solution is 186.4 torr
