[Dave13636]

In lab, you have chosen to examine the properties of an ideal mixture of tetrahydrofuran (THF, C4H8O)
and dimethyl sulfoxide (DMSO, (CH3)2SO). You decide to mix 249 mL of THF and 671 mL of DMSO at
a temperature of 25C and find that the resulting solution has a density of 1.031 g/cm3. You measure the
vapor pressure of THF over the solution to be 47.0 mm Hg. From the CRC Handbook, you nd that at
25C, the densities of pure THF and DMSO are 0.889 g/cm3 and 1.100 g/cm3, respectively, and that pure
DMSO has a vapor pressure of 0.425 mm Hg at 25C and a normal boiling point of 189C. Unfortunately,
you were not able to find any data on THF except that the normal boiling point is 66C.
(a) Based on your knowledge of intermolecular interactions, explain why THF and DMSO might be miscible.
(b) What is the molarity and molality of THF in the DMSO solution?
(c) What are the mole fractions of each component in the solution?
(d) What is the total vapor pressure over the solution due to both the DMSO and THF?
(e) What is the vapor pressure of pure THF at 25C?
(f) Using the Clausius-Clapeyron equation for each component, determine the total vapor pressure of the
solution if you increased the temperature to 45C. Compare this value with the one you computed in step (d).
(g) The mole fractions of each component in the vapor phase can be determined using the partial pressures
of each gas relative to the total pressure. What are the mole fractions of both THF and DMSO in the vapor
phase at 25C and 45C?
(h) What does the difference in composition (mole fractions) between the vapor and solution phases say
about the difference in volatility between THF and DMSO?
(i) Based on what you've found out about how the composition of the liquid    differs from that of the vapor,
do some research about fractional distillation and explain how you might go about extracting pure THF
from your current mixture. Based on your findings above, would it be more efficient to do the distillation at
25C or 45C?

[kyle1990]

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