Question

The vapor pressure of pure hexane and pure pentane at 25^oC are respectively 149.1 mmHg and 508.5 mmHg. What are the approximate vapor pressures (mmHg) of hexane and pentane above a hexane/pentane mixture at 25^oC that has a mole fraction of hexane equal to 0.50?

A. 150 mmHg and 510 mmHg

B. 75 mmHg and 250 mmHg

C. 150 mmHg and 250 mmHg

D. 75 mmHg and 510 mmHg

Answer 1

option b

vapor pressure = mole fraction x  vapor pressure of pure solvent

vapor pressure of hexane = 0.50 x 149.1 =74.55= 75 mmHg

mole fraction of pentane = 1- 0.5 =0.50

vapor pressure of pentane=0.50 x 508.5=254.25 approx 250 mmHg