| Aim | To characterize and purify a chemical substance through the determination of melting point and boiling point, and the process of crystallization. |
| Apparatus Required | Organic compound (unknown) Melting point apparatus Boiling point apparatus Glass capillary tubes Thermometer Distilled water Filter paper Beaker Stirring rod Bunsen burner Alum or Copper Sulphate or Benzoic Acid (impure sample) Erlenmeyer flask Hot plate Vacuum filtration setup |
| Theory | Melting point and boiling point determination are essential methods to characterize and identify an organic compound. The melting point of a substance is the temperature at which it changes from a solid to a liquid, while the boiling point is the temperature at which it changes from a liquid to a gas. Crystallization is a method used to purify an impure substance by dissolving it in a suitable solvent, followed by cooling to obtain a pure crystalline solid. |
| Procedure | (1) Determination of Melting Point: Pack a small amount of the organic compound into a glass capillary tube. Insert the capillary tube into the melting point apparatus. Heat the apparatus slowly and record the temperature at which the substance melts. Allow the substance to cool and repeat the process twice more. (2) Determination of Boiling Point: Add a small amount of the organic compound to the boiling point apparatus. Insert the thermometer into the apparatus. Heat the apparatus slowly and record the temperature at which the substance boils. (3)Crystallization: Dissolve the impure sample of Alum, Copper Sulphate, or Benzoic Acid in distilled water in an Erlenmeyer flask. Heat the flask on a hot plate until the substance dissolves. Remove the flask from the heat source and allow it to cool. Crystals will form as the solution cools. Filter the crystals using a vacuum filtration setup. Wash the crystals with distilled water and allow them to dry. |
| Observation and Result | (i) Determination of Melting Point: Observation: The organic compound will melt and the melting point will be recorded. Result: The recorded melting point is compared with known values to identify the substance. (ii)Determination of Boiling Point: Observation: The organic compound will boil and the boiling point will be recorded. Result: The recorded boiling point is compared with known values to identify the substance. (iii)Crystallization: Observation: The impure sample dissolves in the solvent and forms crystals upon cooling. Result: The crystals obtained are pure and the melting point can be determined to identify the substance. |
