7. A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 250 torr. Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature. What is the mole fraction of hexane?

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Chemistry

20 July, 00:19

7. A solution contains a mixture of pentane and hexane at room temperature. The solution has a vapor pressure of 250 torr. Pure pentane and hexane have vapor pressures of 425 torr and 151 torr, respectively, at room temperature. What is the mole fraction of hexane?

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Monserrat · Answer 1

mole fraction hexane 0.64

Explanation:

We know from Raoult's law of partial pressures that for a binary mixture, the vapor pressure above solution is the sum of the partial pressures of each gas:

P total = P (A) + P (B)

Also the partial pressure of a component is the product of its mole fraction, X, times its pure vapor pressure:

Ptotal = X (A) Pº (A) + X (B) Pº (B)

Since for solution of two components the mole fractions add to one, we now have all the information required to compute the answer.

250 torr = X (hexane) 151 torr + (1 - X (hexane)) 425 torr

250 = 151X (hexane) + 425 - 425 X (hexane)

274 X (hexane) = 175

X (hexane) = 1 - 0.6 = 0.64