We’re being asked to determine the vapor pressure of a solution contains twice as many moles of heptane as octane?
Recall that the vapor pressure of a solution can be given by Raoult’s Law.
The given solutions are composed of heptane and octane, which are both volatile. For a solution with volatile solute and solvent, Raoult’s Law is given as:
where P˚ = vapor pressure of pure component and χ = mole fraction of component. Recall that the mole fractions in a solution add up to 1. Since the solution is composed of heptane and octane, this means:
At 40°C, heptane has a vapor pressure of about 91.5 torr and octane has a vapor pressure of about 31.2 torr. Assuming ideal behavior, what is the vapor pressure of a solution that contains twice as many moles of heptane as octane?
A. 81.8 torr
B. 51.3 torr
C. 10.4 torr
D. 71.4 torr
E. 61.0 torr
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