Distillation.pdf - Microsoft Edge online.ksu.edu/COMS/player/content/_16794/cont
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Distillation.pdf - Microsoft Edge online.ksu.edu/COMS/player/content/_16794/content/Modules/Distillation.pdf 6 0O vapors pass through a distillation head and condenser where the vapors liquify and the liquid collected. The condensed liquid is usually collected in another round bottom flask, but graduated cylinders and erlenmeyer flasks also make suitable collection vessels. A typical simple distillation apparatus is shown in Figure 5-6. Simple distillations are useful in procedures where a solvent is being separated from a non-volatile reaction mixture, or when the boiling points of the liquids to be separated differ by at least 75°C. Because simple distillations have at best 2 theoretical plates, the composition of the condensate is about the same as the composition of the vapor above the boiling liquid. For this reason, liquids with similar boiling points cannot be separated using a simple distillation. FRACTIONAL DISTILLATION Fractional distillations are used when the boiling points of the liquids to be separated are close together and when a better separation of the liquids is necessary for experimental reasons (isolation of a reaction product from a mixture for example). In these distillations, a fractionating column is placed between the distillation head and the condenser. Fractionating columns can be prepared by packing a hollow tube packed with some porous material (steel wool or glass beads for example This material provides a surface on which distillation vapors can cool condense, and re-vaporize. Referring back our 80:20 mixture of methanol and propionic acid, the vapor just above the liquid would be in equilibrium with a vapor whose composition is described by point V, 64% methanol, 36% propionic acid. Near the bottom of the column, the vapors would condense to give a liquid with the same composition, L2. This liquid would then be in equilibrium with vapor V2, with a composition of 94% methanol, 6% propionic acid. These vapors would then condense to form a liquid with the same composition at point L3. The further up the column the distillate travels, the richer in methanol it becomes, and if we have added enough theoretical plates, the liquid-vapor equilibrium mixture at the thermometer should be pure methanol. That is, the boiling point reading should be the same as that for pure methanol. The fractional distillation apparatus used in the organic lab is shown in Figure -5- 7. These fractionating columns have 3-5 theoretical plates DISTILLATION CURVES Ask me anything 2:33 PM 12/20/2015Explanation / Answer
40 mL x 0.89 g/mL / 102.1 g/mol = 0.35 mol MB
10 mL x 0.96 g/mL / 88.1 g/mol = 0.11 mol BA
Total moles ……………………..0.46 mol
MB mol % = 100 x 0.35/0.46 = 76%
BA mol % = 100 x 0.11/0.46 = 0.24%
(in the image try to draw the first vertical line closer to MB80%.
1.The boiling point is the temperature of the first horizontal line, my estimation is about 103..104ºC.
2. look at the left end of the first horizonthal line, draw a vertical line and read the composition on the abscissa : 95% MB and 5% BA. These values are the vapour composition and the composition of the distillate for a simple distilation (same values).
3. Each horizontal line is a vaporizaton. Each vertical line is a condensation. Each pair vaporization-condensation is a theoretical plate. For three theoretical plates, the distillate (first fraction) is very close to pure MB (>99%).
Note. Observe that after the collection of the first fraction, you have to rise the temperature to 160 ºC to start a vaporization of the remaining pure BA.
Observe that two theoretical plates are quite enough (see also Table 4.1, the boilig point difference is 60ºC)