The purpose of this experiment is to learn how to separate two miscible liquids by microscale process. There will be use of simple and fractional distillation. Simple and fractional distillation efficiencies will be compared. The student should have knowledge of how to measure volumes of chemical compounds. In addition, the student should know how to make a bent-tip pasture pipette for microscale distilltions.
Distillation is commonly used in chemistry when compounds need to be seperated because of their differences in their boiling points. Many organic compounds are volatile. Meaning they have high vapor pressures and low boiling points. During distillation, volatile compounds are heated to a boiling in container known as a pot. The vapors produced are colled and reliquefied by passing them through a water cooled condenser. They are then collected in seperated container called the receiver. This technique is used to remove a volatile solvent from a non-volatile product, seperating volatile product from impurities, or to separate two or more volatile compounds with adequate difference in boiling points
` When liquid is placed in container, some of the molecules evaporate into unoccupied space inside the container. Evaporation continues until there is equilibrium between the molecules leaving and entering the liquid. The pressure exerted by these gaseous molecules on the walls of the container is the equilibrium vapor pressure. The magnitude of this pressure depends on the physical properties of the compound and temperature increases
Liquid is converted to vapor more rapidly by boiling than evaporating. If the heating rate is increased. The temperature of the boiling liquid does not change, but the rate at which vapor is produced from the liquid increases
Transfer 25 ml of cyclohexane and 25 ml of toluene into a 50 conical vial and add a couple of small boiling chips. Attach the hickman still head and clamp the apparatus vertically in a sand bath. Place a thermometer through the center opening of the thermometer adapter thermometer bulb inclose enough to the bottom of the collar. Raise the volt into about 70 C and wait to get the first drop in the receiver. Record the temperature each time you get 5 ml in the flask. As the flask is heated, the lower boiling liquid vaporizes faster than the higher boiling liquid. Thus, although both components are in the vapor phase, the vapor is richer in the lower boiling liquid.
The resulting vapor could be condensed and re-evaporated. If you stop too early, you will not have enough data for a good distillation graph. The temperature at the end of your experiment should be at least 105°C and preferably more, unless your pot is about to distil to dryness before this happens. You must stop while there is still liquid in the pot. Also, If you place the thermometer bulb too high, the vapors won’t reach it before they go into the sidearm to be collected, and your observed boiling point will be lower than it should be. If you place the thermometer bulb too low, vapors of impurities may reach it, giving a high reading for the boiling point range.
This was a very simple lab but there still seemed to be room for procedure errors. The first temperature range sample came out as desired with 100% Cyclohexane because its boiling point is right on that range. However, there seemed to be too much cyclohexane in the higher temperature samples. It was expected that by heating, the solution at 100˚C would be completely toluene but this was not true. The most likely reason for this is that we did not allow the solution to heat enough at 80-90˚C to allow most of the cyclohexane to evaporate out. The experiment should be done again with more patience to allow the compounds to evaporate out completely at their given boiling points.