1 Simple Distillation ABSTRACT Simple distillation is a method used to separate liquids through 1-3 condensations and vaporizations. The boiling point of the different liquids causes the van der Waals forces to break and the liquids separate. In the following experiment 2 liquids were separated using the simple distillation method. Following the experiment it was determined that the two liquids were hexane and ethanol. INTRODUCTION When two liquids are mutually soluble their molecules interact with one another by van der Waals forces. In order to separate the liquids, they can go through a process called distillation. Distillation allows one to separate liquids by exploiting vapor pressure differences of the components. There are many different methods of distillation, but the method of this report is simple distillation. Simple distillation allows 1 to 3 vaporizations and condensations. In simple distillation, the distillation flask should be 1/3 to ½ full so the solution does not get bumped into the condenser. In the simple distillation apparatus, there is a simple adapter that allows solutions to be condensed. Once condensation begins the temperature is watched to observe if any significant changes in temperature occur. Any drastic temperature changes in temperature can indicate that liquid of higher boiling point is now being vaporized as temperature increases. MATERIALS & METHODS  Round Bottomed Flask  Water  Ring stand  Magnetic stir plate  Unknown B  Rubber Tubing  Thermometer adaptor  Thermometer 2  Grease  Condenser  Graduated cylinder  Receiving adaptor  Distillation adaptor  Magnetic stir bar  Support clamps  Heating mantle  Generator  Conical funnel The heating mantle is a mechanism used to heat glassware and its contents. A magnetic stir plate was used to cause the magnetic stir bar to stir the solution while connected to the simple distillation apparatus. The simple distillation apparatus is used to separate liquids through evaporation. Heat is applied to the bottom of a round bottomed flask that contains the solution and separates them through evaporation as different liquids have different boiling points. As one of liquids evaporates it travels through the apparatus in its gaseous state and condenses in a receiving adaptor dripping into another round bottom flask. Dramatic temperature change is used to determine which liquid is being condensed at the time of collection. Water MW: 18.02 g/mol Density: 1 g/cm3 Ethanol MW: 46.07 g/mol Density: 0.789g/cm3 PROCEDURE Hexane MW: 86.18 g/mol Density: 0.659 g/cm3 3 1. Round bottomed flask was selected that was filled to 1/3 to ½ of the unknown B and placed in a clamp to be attached to the ring stand. The unknown B was then placed in the flask containing a magnetic stir bar through a conical funnel. 2. The bottom and side piece of the distilling adaptor were then lightly greased and connected to the round bottomed flask and the adapter. 3. Rubber tubing is connected to the condenser on the “water in” and “water out” openings. The “water in” tube was connected from the sink to the condenser. The “water out” tubing was connected from the condenser to the drain of the sink. 4. The condenser was then placed on a ring stand using a clamp. The condenser was greased and connected to a receiving adaptor that was greased and placed over a graduated cylinder. 5. The thermometer adapter was greased and attached to the distillation head. The thermometer was placed through the adapter and pushed beside the opening of the condenser. 6. Lastly, the magnetic stir plate and heating mantle are plugged into a generator and placed underneath the round bottomed flask containing the unknown solution. The apparatus was then checked to for before use. 7. The magnetic stir plate was set between 2 and 3. The heating mantle was then set to 6. DIAGRAMS 4 RESULTS & DISCUSSION After the simple distillation process, the data was used to determine that the liquids in the unknown B were hexane and ethanol. The experiment resulted in hexane and ethanol due to the first drop of liquid was recorded at 65°C near the boiling point of hexane. The data below also shows a dramatic change in temperature near the 90 mL mark showing that ethanol had begun condensing. The 90 mL mark gave an estimate of 90 mL of hexane and 10 mL of ethanol of the 100 mL solution. The unknow solution B was calculated to be 93.37% hexane and 6.63% ethanol. 5 CALCULATIONS Unknown B obtained: 100 mL Hexane-90 mL 3 90 mL× .0659 g /cm =59.31 grams 59.31 g ÷ 86.18 g/ mol=1.29 mol Ethanol- 10 mL 3 10 mL× 0.789 g /cm =7.89 grams 6 7.89 g ÷ 46. 07 g =0.0916 mol mol Mole Fraction Hexane 1.29 mol of Hexane ×100=93.37 % Hexane 1.29mol +0.0916 mol Ethanol 0.0916 mol of Ethanol ×100=6.63 % Ethanol 1.29 mol+ 0.0916 mol SAFETY AND DISPOSAL According to the lab instructor all chemicals used were safe to be disposed down the sink drain. Glassware was rinsed and dried after use and placed back into equipment drawers. The heating mantle was cooled before placing back in its designated drawer along with the generator and heating mantle. CONCLUSION The unknown B was determined to be a mixture of hexane and ethanol. After observing the first drop of condensation at 65°C it was determined that the hexane was the first liquid to be condensed due to its boiling point. Considerable change in temperature at around 78°C determined that ethanol was the second liquid to condense with 10 mL left of the solution. 7 According to mole fraction 93% of the solution was hexane and around 7% of the solution was ethanol. General error that could have interfered with accurate results may have been to loss of condensation through apparatus connection or increasing heat rate of heating mantle causing the change in temperature to be disturbed. POST-LAB QUESTIONS 1. Explain why the observed boiling point for the first drops of distillate collected in the simple distillation of a 1:1 molar solution of pentane and hexane, illustrated in Figure 12.5, will be above the boiling point of pentane. 8 The first drops of the distillate are a mixture of the both hexane and pentane. The first vapor is comprised of mostly hexane, which has a higher boiling point. With the solution being a mixture of the two the boiling point is going to be higher. 2. The molar composition of a mixture is 80% hexane and 20% pentane. Use the phase diagram in Figure 12.4 to estimate the composition of the vapor over this liquid. This vapor is condensed, and the resulting liquid is heated. What is the composition of the vapor above the second liquid? The composition of the vapor over the second liquid will be 20% hexane and 80% pentane. 3. A student carried out a simple distillation on a compound known to boil at 124°C and reported an observed boiling point of 116-117°C. Gas chromatographic analysis of the product showed that the compound was pure, and a calibration of the thermometer indicated that it was accurate. What procedural error might the student have made in setting up the distillation apparatus? The error might be due to the thermometer was not correctly placed in the neck of the distillation flask. If the bulb of the thermometer was placed above the distilling flask side arm, the temperature at that location probably is less than the boiling point.