Lab 3 - Fractional Distillation Lab report PDF

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IV: Results of Corrected Refractive Index

Table 1: simple and fractional distillation graph

Temperature vs Volume of Cyclohexane-toluene Mixture 110

Temperture in C

105 100 95 90 85 80 0

2

4

6

8

10

12

14

16

18

20

Volume of distillate (mL)

A simple distillation shows a gradual increase of temperature with volume of distillate. A fractional distillation is more S-shaped and shows a plateau at the beginning indicating that the cyclohexane compound distilled first having the lowest boiling point, then a rapid rise in temperature during which time a mixture of both components, cyclohexane and toluene distilled.

Post-lab Questions 1. What is the best procedure for separating two miscible organic liquids that have over 150 degrees difference in their boiling points (e.g., a volatile and a non-volatile liquid)? What is the best procedure for separating two miscible organic liquid which have only a few degrees difference in their boiling points (e.g. two relatively volatile liquids)? - Simple distillation is a method used for the separation of components of a mixture containing two liquids that boil without decomposition and have sufficient difference in their boiling points. - Fractional distillation is used for the separation of a mixture of two or more liquids for which the difference in boiling points is less than 25K. 2. Refer to the boiling point-composition curves (shown here) for mixtures of liquids A and B. a) What is the boiling point and composition of liquid L1? - Boiling point: 85 degrees Celsius - Composition: A= 0% B = 100 % b) What is the composition of its vapor? - V2 - Composition: A= 20% B= 80% c) If this vapor is recondensed to a liquid, what will be its boiling point and its boiling point and its composition? - At L2 boiling point of about 75 degrees and a composition of A= 20% and B= 80% 3. Discuss two factors that affect the efficiency of a fractional distillation and how they affect efficiency - You can improve the purity of the fraction by increasing the surface area of the fractionation column. The longer the vapors take to reach the top of the column, the higher the purity of the fraction and the greater the efficiency of the column. Solubility also affects fractional distillation because the tendency of specific substances to dissolve to form a homogeneous solution affects how well a substance can be separated via distillation. 4. Calculate the mole fraction of each component in solution if you mix 67.2 g of toluene and 22.7 g of cylcohexane, assuming Mwt of toluene is 92 g/mole, and Mwt of cyclohexane is 84 g/mole. (show your calculations) Mass of Toluene = 67.2 g (mol.wt.= 92 g/mol) Given mass of cyclohexane = 22.7g (mol.wt.= 84 g/mol) No. Of moles of Toluene(nA) = 67.2 g / 92 g/mol= 0.73mol

No. of moles of cyclohexane (nB)= given mass/mol.mass = 22.7 g / 84 g/mol = 0.27 mol Mole fraction of Toluene (NA)= nA/(nA+nB) =0.73 / (0.73 + 0.27) = 0.73 Mole fraction of cyclohexane (NB)=nB/(nA+nB) = 0.27/ (0.73 + 0.27)=0.27 5. a) Assuming that this solution of cyclohexane and toluene is an ideal solution that follows Dalton’s and Raoult’s laws, what is the partial vapor pressure of cyclohexane and toluene in the solution at 100°? (show your calculations) PA=P°ANA PA= 1311× 0.73 = 957.03 mmHg PB= P°BNB PB (partial vapor pressure of cyclohexane) = 556 × 0.27 = 150.12 mmHg b) Would this solution boil at 100° if the surrounding pressure is 760 mm Hg? Explain - Yes because there is a high increase in mmHg c) What is the composition of the vapor at 100°? (show your calculations). Is the vapor (and the resulting recondensed liquid) now richer in cyclohexane than the percent of cyclohexane in the original liquid mixture? (show your calculations) Does this composition follow theory of what it should be? - Xc = 405.88 / 760 = 0.53 or 53% - Xt = 353 / 760 = 0.47 or 47% - Yes, this composition follows the theory that hexane has a greater percentage than toluene. 6. What is the corrected refractive index at 20° if a reading of 1.3527 was observed at 18°? Show your calculations. 1.3527 + 0.0045 x (18.0-20) = 1.3518...