09 Distillation

DISTILLATION Introduction To distil is to boil a liquid condensing its vapours in a separate container. Thus we can separate solutions containing a liquid and a solid. For example: a solution of sugar in alcohol can be carefully distilled: alcohol will boil and escape through the side – tube, then it will condense in a condenser (a tube sheathed with another one through which cold water flows to refrigerate the out coming vapours) and will be collected in a conical flask or in a test tube. Sugar will remain in the distillation flask. The thermometer shows the temperature of the substance that distils. When a solution of two or more liquids has to be separated, when one of them is distilling the other one will be dragged off the flask and so it will co- distil. To avoid this, fractional distillation columns are used. These are long columns filled with glass beads, or porcelain sticks, or anything that increases the inner surface of the column, and lagged with any insulating material to prevent heat (energy) losses. The vapours condense in the column (beads etc.) making it hot. When the column is hot enough, the most volatile (lowest boiling point) substance will pass through and get to the condenser. The less volatile will condense and drip back into the distillation flask and so both liquids will be separated. Aims To study the separation of a water – methanol mixture with a simple distillation and a fractional distillation apparatus. Apparatus Distillation flask, round bottom flask, pierced bungs, thermometer, condenser, pipette, fractional distillation column, porous stone, Bunsen burner, tripod wire gauze, stand, clamp and nut, test tubes and rack, marker. Procedure

1- Put 8 - 10 test tubes in a rack. Add 5 ml of water to each tube. Mark (use a waterproof marker) the level at 5 ml. Then add another 5 ml and mark the volume 2- Empty the test tubes and let them drip dry as much as possible (put them upside down.

3- Set the apparatus shown in Diagram I. 4- Pour into it a 50 : 50 mixture (by volume) of water and methanol. 5- Add some porous material to avoid overheating (bumping).

6- Prepare a two-column table to write down the volume readings and their corresponding temperatures. (Split it in two sections to save paper and for aesthetic reasons).

7- Light the burner and distil at a gentle rate (one drop per second). 8- Read the temperature when the first drop of liquid is received in the first test tube and when the liquid gets to 5 ml. Write down the data in your table. 9- After 10 ml change the collecting test tube and keep on distilling until the temperature is 100 °C constant. 10- Once the experiment is finished, put out the fire and set the apparatus shown in Diagram II.

11-Repeat steps 4 to 10 and put out the burner. 12-Plot on the same paper both distillation curves (temperature against volume), Stick the plots to the report and compare. improvement?

Diagr Diagram II

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