Boiling Point For Cyclohexane The Distillate example essay topic

INTRODUCTION: Simple distillation is a process to purify volatile compounds or compounds with different boiling points. It is a simple process that takes a mixture of compounds and applies heat. The substance with the lowest boiling point, (usually the most volatile), will boil and vaporize first. Using a distillation apparatus consisting of a flask, glass tubes, thermometer, condensing tube and distillate container, the first gaseous vapor that rises can be condensed back into liquid. This liquid is directed into a separate container and is called the distillate. When the first boiling point is reached the vapors rise.

The vapors that hit the upper side of the flask and thermometer will condense and fall back down to again re-vaporize. The vapors that reach the upper side arm will enter a water-cooled condensing tube where it will condense to liquid form and fall in to a separate distillate container. In Simple Distillation the distillate will contain a higher percentage of the more volatile compound but will not be pure. If the partial pressures are calculated and then divided by the total pressure - the best separation percentage can be calculated. Generally Simple Distillation is only used to separate compounds that have boiling points that differ by at least 80 degrees Celsius. In this Distillation experiment, Cyclohexane is distilled from an equal mixture of Cyclohexane / Toluene.

THEORY: Raoult's Law: The vapor pressure of a compound in a mixture is equal to the product of the vapor pressure of the pure substance and the mole fraction of the substance in the mixture. Dalton's Law: The mole fraction of a substance in the vapor at a given temperature is equal to the partial pressure of the substance at that temperature divided by the total pressure. RESULTS / DATA A mixture of 30 mL Cyclohexane and 30 mL Toluene is added to a flask that contains a boiling chip. The flask is attached to a Simple Distillation apparatus and heat is applied to the flask. The volume of the distillate and the temperature are recorded as the distillate is formed.

Cyclohexane bp 81.4^0 C den. 0.78 M.W. 84.16 CH 3 Toluene bp 110.8^0 C den. 0.87 M.W. 92.13 The atmospheric pressure during this experiment was 760 mm (Hg) Distillate Volume Boiling Point 0 mL 81.4 5 mL 86.0 10 mL 88.0 15 mL 89.9 20 mL 91.0 25 mL 93.0 30 mL 95.0 35 mL 97.0 40 mL 101.0 45 mL 105.0 50 mL 107.5 DISCUSSION: At roughly the boiling point for Cyclohexane the distillate started to form. As the temperature increased the distillate still formed at a steady rate.

The rate of flow continued until the temperature neared the boiling point for the second substance, Toluene. At this point the rate of flow slowed down. On a graph of Temperature vs. Distillate Volume, it is easy to see that there is not a constant boiling point - indicating a lack of purity. A pure substance will have a constant boiling point. To get a greater percentage of Cyclohexane the distillation process can be repeated. Some Points to consider: Calibration of thermometer - Accurate data is achieved with instruments that are accurate and functioning properly.

In this experiment we did not calibrate the thermometer. This could be a source of error. Boiling points of mixtures - Boiling points are a function of atmospheric pressure. The boiling points of most liquids decrease by 0.5^0 C for every 10 mm Hg decrease in atmospheric pressure. CONCLUSION: Using the technique of Simple Distillation and starting with equal amounts of Cyclohexane and Toluene.

The distillate formed had a higher percentage of Cyclohexane but was not pure. The lack of a constant boiling point indicated that the substance was not pure.

Bibliography

Fie ser / Williamson, Organic Experiments, Boston Massachusetts, Houghton Mifflin Company. Spurlock, D, "Purification of Liquids by Simple Distillation" Indiana University Southeast, web.