Question

Calculate the vapor pressure at 85.0°C of a solution prepared by dissolving 0.100 mol of liquid dibromoethane (C2H4Br2, P° = 127 torr) in 1.80 mol of liquid dibromopropane (C3H6Br2, P° = 173 torr)._______ torr

Answer 1

170 torr.

Step-by-step explanation:

To solve this problem we have to understand Dalton's Law: Dalton’s Law, or the Law of Partial Pressures, states that the total pressure exerted by a mixture of gases is equal to the sum of the partial pressures of the gases in the mixture.

The formula is the following:

`P_(TOTAL)=P_A+P_B+...+P_N.`

We have in this case, two solutions, so first, we have to calculate the total number of moles:

`n_(total)=0.100\text{ mol + 1.80 mol=1.90 moles.}`

And now, let's calculate the mol fraction of each solution by dividing the moles of the certain substance by the total number of moles, like this:

`\begin{gathered} mol\text{ fraction of C}_2H_4Br_2=\frac{0.100\text{ mol}}{1.90\text{ mol}}=0.0526, \\ mol\text{ fraction of C}_3H_6Br_2=\frac{1.80\text{ mol}}{1.90\text{ mol}}=0.947. \end{gathered}`

The next step is to calculate the vapor pressure of each substance by multiplying the mole fraction of each solution by its given pressure, like this:

`\begin{gathered} Vapor\text{ pressure of C}_2H_4Br_2=0.0526\cdot127\text{ torr=6.68 torr,} \\ Vapor\text{ pressure of C}_3H_6Br_2=0.947\cdot173\text{ torr=163 torr.} \end{gathered}`

The final step is to sum the total vapor pressure by summing each vapor pressure of each substance:

`\begin{gathered} (Vapor\text{ pressure\rparen}_(TOTAL)=6.68\text{ torr+163 torr,} \\ (Vapor\text{ pressure\rparen}_(TOTAL)=169.68\text{ torr}\approx170\text{ torr.} \end{gathered}`

The answer would be that the total vapor pressure is 170 torr.