Question

At a certain temperature the vapor pressure of pure heptane (C_7 H_16) is measured to be 170. torr. Suppose a solution is prepared by mixing 86.7 g of heptane and 125. g of acetyl bromide (CH_3 COBr). Calculate the partial pressure of heptane vapor above this solution. Round your answer to 3 significant digits. Note for advanced students: you may assume the solution is ideal.

Answer 1

Step-by-step explanation:

The given data is as follows.

Pressure (P) = 170 torr, mass of heptane (m) = 86.7 g

First, we will calculate the number of moles as follows.

No. of moles =
`\frac{mass}{\text{molar mass}}`

=
`(86.7 g)/(100 g/mol)`

= 0.867 mol

Now, the number of moles of
`CH_(3)COBr` are calculated as follows.

No. of moles =
`\frac{mass}{\text{molar mass}}`

=
`(125)/(122.9)`

= 1.07

Therefore, mole fraction of heptane will be calculated as follows.

Mole fraction =
`\frac{\text{moles of heptane}}{\text{total moles}}`

=
`(0.867)/(0.867 + 1.07)`

=
`(0.867)/(1.937)`

= 0.445

Now, we will calculate the partial pressure of heptane as follows.

`P_(A) = x_(A)P^(o)_(A)`

=
`170 * 0.445`

= 75.65 torr

Thus, we can conclude that the partial pressure of heptane vapor above this solution is 75.65 torr.