Heating Methods Reflux and Distillation
Heating Methods Reflux Distillation
Reflux You will use this next lab for the synthesis of aspirin not in this lab experiment Heating the reaction contents without 1) losing solvent and 2) without building up pressure in the reaction vessel Please watch the video posted on reflux found in the website
Reflux Thermometer Actual student setup Notice where all the clamps are located! Condenser Round bottom flask Water bath (if solvent boils under 100ºc) Hot plate (new)
heating a liquid mixture to its boiling point, where liquid is rapidly converted to vapor. The vapors, richer in the more volatile component, are then condensed into a separate container. The components in the mixture have sufficiently different vapor pressures (or boiling points), they can be separated by distillation. Experimental procedure modifications: No Gas Chromatography (GC) You will check the identity of the distillates by IR Spectroscopy instead
You will be given an unknown mixture of two organic chemicals Goals: separate the two using ONLY simple distillation Obtain BP for each compound Obtain IR spectra for each compound Determine the identity of each compound with BP and IR data Create a distillation curve (time vs. volume of distillate collected) Collect distillates here but in a graduated cylinder instead
Performing a simple distillation, assemble the apparatus shown in Figure 14.1. Use a 50-mL roundbottom flask as the distilling and replace the receiving flask with a graduated cylinder to create the distillation curve. Carefully note the position of the thermometer The bulb of the thermometer or the bottom of the temperature probe must be placed below the sidearm, or it will not read the temperature correctly.
For the simple or fractional distillation, place several boiling stones into the 50- ml round-bottom flask. Also add 28.0 ml of the unknown mixture (measured with a graduated cylinder) to the flask. Use a heating mantle for heating (used for heating compounds that have a BP higher than 100ºc). Start circulating the cooling water in the condenser and adjust the heat so that the liquid boils rapidly. During the initial stages of the distillation, continue to maintain a rapid boiling rate. As the hot vapors rise, they will gradually heat up the glassware. Because the mass of glass and other materials is fairly large, it will take 10 20 minutes of heating before the distillation temperature begins to rise rapidly and approaches the boiling point of the distillate. When the temperature begins to level off, you should soon see drops of distillate falling into the graduated cylinder.
Turn down the heat control to achieve the desired rate of distillation. In addition, it may be helpful to lower the heating mantle slightly below the round-bottom flask for a minute or so to cool the mixture more quickly. You should also begin recording the distillation temperature as a function of the total volume of distillate collected. Beginning at a volume of 1.0 ml, record the temperature at every 1.0-mL interval, as deter- mined by the volume of distillate in the 25-mL graduated cylinder. After you have collected 4 ml of distillate, remove the graduated cylinder and collect the next few drops of distillate in a small leak-proof vial.1 Label the vial 4-mL sample. Cap the vial tightly; otherwise, the more volatile component will evaporate more rapidly, and the composition of the mixture will change. Resume collecting the distillate in the graduated cylinder. As the distillation temperature increases, you may need to turn up the heat control to maintain the same rate of distillation
After the first component has distilled, it is possible that the distilling temperature will drop significantly. Continue to record the temperature and volume data. When you have collected a total of 20 ml of distillate, take another small sample of distillate in a second small vial. (If the total volume of distillate that you can collect is less than 20 ml, take the last few drops as your second sample.) Cap the vial and label it 20-mL sample. Then continue the distillation until there is a small amount (about 1.0 ml) of liquid remaining in the distilling flask. Do not distill to dryness! A dry flask may crack if it is heated too hot.
Distillation Curve. Using the data you collected for the distillation temperature and the total volume of distillate. Plot the volume in 1.0-mL increments on the x-axis and the temperature on the y-axis. Estimate the boiling points of the two components in your mixture by noting the two regions on the graph where the temperatures leveled off. From these approximate boiling points, try to identify the two liquids in your mixture (see table shown at the beginning of this experiment). Note that the observed boiling point for the first component may be somewhat higher than the actual boiling point, and the observed boiling point for the second component may be somewhat lower than the actual boiling point. NO Gas Chromatography No fractional distillation