CHEN 354—HW 11—Due Friday, Nov. 21
Problem 1. Benzene and water are virtually immiscible. What is the bubble pressure of an overall
mixture that is 50 mol% of each at 75oC?
Problem 2. Water + hexane and water + benzene are immiscible pairs.
(a) The binary system water + benzene boils at 69.4oC and 760 mm Hg. What is the activity coefficient of
benzene in water if the solubility at this point is xB =1.6 E-4, using only this information and the Antoine
coefficients?
(b) What is the vapor composition at the bubble pressure at room temperature (292 K) for a ternary
mixture (water, benzene, hexane) consisting of 1 mole overall of each component if the organic layer is
assumed to be an ideal solution?
(c) What is the vapor composition at the bubble pressure for a ternary mixture (water, benzene, hexane)
consisting of 1 mole overall of each component if the activity coefficients of the organic layer are
Horg=1.12 and Borg = 1.18.
Problem 3. The bubble point of a liquid mixture of n-butanol and water containing 4 mol% butanol is
92.7oC at 1.103 bar. At 92.7oC the vapor pressure of pure water is 0.784 bar and that of pure butanol is
0.427 bar.
a. Assuming the activity coefficient of water in the 4 mol% butanol solution is about 1, what is the
composition of the vapor in equilibrium with the 4mol%butanol-water mixture, and what is the activity
coefficient of n-butanol?
b. At 92.7oC, the maximum amount of n-butanol that can be dissolved in water is 4 mol%. When larger
amounts of n-butanol are present, a second liquid phase containing 40 mol% n-butanol, appears. What
are the activity coefficients for n-butanol and water in this second liquid phase?
c. If the two coexisting liquids in part (b) are kept at 92.7oC, what will be the pressure when the first
bubble of vapor is formed?
Problem 4. A 50 wt% (22.5 mol%) solution of ethylene-glycol and water freezes at 240 K.
What freezing temperature would be predicted by assuming that ethylene glycol and water form an
ideal solution? The freezing occurs by formation of water crystals.
Estimate the activity coefficient of water using the experimental freezing temperature of 240K.
Problem 5. Estimate the solubility of naphthalene (1) in nitrogen (2) at 35oC at pressures up to 300 bar.
Use the procedure in section 14.7 with l12 =0. Compare the results with those in Fig. 14.23 for
naphthalene/CO2 at 35oC with l12 =0. Discuss any differences.