Tools

Purification by Fractional distillation/crystallisation

Procedure

Fractional Distillation:

  1. Take the mixture to be separated in an R.B flask.
  2. Add some porcelain pieces in the flask to avoid bumping.
  3. Fit the R.B flask with an adapter & attach a fractionating column.
  4. Introduce a thermometer. (The top of the thermometer bulb should be just below the side arm of the distilling flask, ensuring that the entire thermometer bulb will be bathed in the rising vapour as the liquid mixture is heated).
  5. Connect a Liebig's condenser to the side tube of the adapter.
  6. Circulate water from the lower end of the condenser, prior to heating the R.B flask.
  7. Gently heat the flask until the liquid begins to boil.
  8. Lower the heating rate and heat slowly at a constant rate to permit a good separation.
  9. Continue boiling the liquid until the temperature remains the same for about 3–4 minutes & then rises quickly.
  10. Collect the distillate in a receiving flask.

Points to Remember while Performing the Experiment in a Real Laboratory:

  • Always wear lab coat and gloves when you are in the lab.
  • When you enter the lab, switch on the exhaust fan and make sure that all the chemicals and reagents required for the experiment are available. If not, prepare the reagents using the appropriate components.
  • Properly adjust the flame of the Bunsen burner. The proper flame is a small blue cone; it is not a large plume, nor is it orange.
  • Clean all your working apparatus with chromic acid and distilled water. Ensure all apparatus are free from water droplets.
  • Calibrate the electronic weighing balance before taking measurements.
  • Ensure that the desiccator has a sufficient amount of desiccant (e.g., silica gel).
  • Use chromic acid to clean the crucible. Heat it, cool it, and place it in the desiccator using clean tongs or tissue paper. Do not touch it with your hands.
  • Switch on the oven and adjust the temperature to 130°C. Use cotton gloves when working with the hot air oven.
  • Clean the Kipp's apparatus tube with water. Ensure it contains sufficient solid material (iron sulfide) and H2SO4 for producing H2S gas.
  • Clean all glassware with soap and distilled water. Recap reagent bottles after use.
  • Switch off the light, exhaust fan, hot air oven, and gas cylinder before leaving the lab.
  • Discard used gloves in a waste bin.