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Vacuum Filtration - Method for Experiment 3

Essay by   •  April 12, 2019  •  Coursework  •  721 Words (3 Pages)  •  1,589 Views

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  1. Weight out approximately 0.71 g of the salicylic acid.and put it into a 100mL conical flask
  2. Use a measuring cylinder to measure out 2 mL of propionic anhydride and add into the conical flask.
  3. To the flask add 3 - 5 drops of concentrated sulfuric acid(corrosive) in the fumehood.
  4. Swirl gently and warm the mixture in a hot water bath on a hotplate. Put a stopper loosely on the conical flask to prevent evaporation.
  5. Swirl until all the solid has dissolved and then warm it for another 5 minutes.
  6. Carefully add 10 mL of cold distilled water to the solution in conical flask and followed by slow addition (1 mL at a time) of 10 mL of 1M sodium hydroxide solution.
  7. Check the pH of the solution by using pH paper.
  8. Dip a stirring rod into the conical flask and then place the solution on a piece of pH paper. Make sure the pH is > 7. If not, continue adding the sodium hydroxide until basic pH is reached.
  9. Stand the flask in a bath of iced water until precipitation appears to be complete. It may be necessary to stir vigorously with a glass rod to start the precipitation process.

Vacuum Filtration

  1. Weigh the watch glass with filter paper before filtration.
  2. Filter off the precipitate using a Buchner funnel and suction apparatus. You may need to rinse the conical flask with some amount of water to remove all the solids in the conical flask.
  3. Wash the conical flask with 2 mL of distilled water to prevent residue leftover, transfer the filter paper with crystals to a weighed watch glass and leave to dry in an oven (80°C). Weigh your crystal until constant mass is obtained.
  4. Determine the total mass of your crude product.


  1. Transfer the crystal into a 50mL conical flask.
  2. Add 5 mL of ethanol and swirl gently while warm the solution on the hot plate to dissolve.
  3. Add a few drops of cold distilled water into the solutions. Allow the solution to cool slowly to begin precipitation. If no signs of precipitation, add a few more drops of cold distilled water and stir vigorously for a few minutes.
  4. Leave your mixture for a few minutes to be cold.
  5. Weigh the watch glass with filter paper before filtration.
  6. Filter the solid by using a Buchner funnel and pump to make sure that the precipitate is completely dry. Leave it in an oven (80°C) to ensure water was completely removed.
  7. Weight the recrystallize solid until constant mass is obtained and record the weight.


Thin Layer Chromatography (TLC) Test

  1. The plate is prepared by ruling a line about 1.5 cm above the bottom edge using a pencil.
  2. Spot a small, concentrated of the mixture on this line using a TLC spotter.
  3. Salicyclic acid is labelled as 1 and mixture synthesized is labelled as 2.
  4. Use a 100 mL beaker for the development of your TLC plate. The solvent to use for this separation is (Hexane:Ethyl acetate with ratio 50:50).
  5. By the time the solvent has travelled almost to the top of the plate, the mixture will have separated out into its different components.
  6. The plate is removed from the beaker and allowed to dry.
  7. If the sample is coloured, the results can be viewed with a ultra-violet lamp. Mark the position of the components.
  8. Measure the distance travelled by the components.

Melting point Test

  1. Place a small amount of white powder in the end of a glass capillary tube.
  2. Press and hold the plateau set button (the plateau light will flash). Current temperature will be shown on the display.
  3. The desired plateau temperature may now be set using the arrow keys to scroll the display up or down as required.
  4. Insert the tube into the side of the heating block via the holes provided at either side of the machine. Look down the magnifier and position the tube so that the sample can be observed clearly. Caution: The heating block may be HOT.
  5. Press the start key. The unit will quickly heat up to the plateau temperature.
  6. Observe the sample until the melt occurs and record the temperature from the digital display.
  7. After the melt has occurred press the stop button. All the function light will turn off and the unit will starts to cool to ambient temperature.



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