Question

(i) A solution of toluene (methyl benzene) and ethanoic acid is said to exhibit “positive deviations from Raoult’s Law”. Discuss 1) how the graphical evidence obtained from partial pressure measurements as a function of composition would prove it exhibits positive deviations and 2) why it deviates using a molecular-based explanation. Please be specific to the system in question in your explanations.

(ii) The acetone-cyclohexane system also exhibits positive deviations from Raoult’s Law. Sketch the expected temperature-composition phase diagram for this system given the following: bp (pure acetone) = 56.5ºC, bp (pure cyclohexane) = 81.4ºC, azeotrope occurs at ca. 0.25 mole fraction cyclohexane and boils at 53 ºC. All bp’s are cited for P = 1 atmosphere. State the two possible eventual outcomes if mixtures of acetone and cyclohexane were repeatedly distilled in an effort to separate the two components completely (give what would be expected as a distillate and what would be expected to be left in the distillation flask for starting solution compositions having a mole fraction of cyclohexane less than or greater than the azeotrope composition).

Answer 1