Question

The vapor pressure of pure water at 85oC is 434 torr. What is the vapor pressure at 85oC of a solution prepared from 100 mL of water (density 1.00 g/mL) and 150 g of diglyme, C6H14O3, a nonvolatile substance?

Answer 1

Answer:

$P=361.2torr$

Explanation:

Hello,

In this case, considering that the formed liquid is solution is ideal, we can relate the vapor pressure and molar fraction of water with the total vapor pressure of the solution by using the Dalton's equilibrium-based law:

$P=x_{H_2O}P_{H_2O}^v$

In such a way, we compute the molar fraction of water by computing its moles as well as diglyme:

$n_{H_2O}=100mL*\frac{1g}{1mL} *\frac{1mol}{18g} =5.56molH_2O\\\\n_{C_6H_{14}O_3}=150g*\frac{1mol}{134g}=1.12molC_6H_{14}O_3$

Thus, the mole fraction of water:

$x_{H_2O}=\frac{5.56mol}{5.56mol+1.12mol}=0.832$

Thereby, the vapor pressure of the solution:

$P=0.832*434torr\\\\P=361.2torr$

Regards.