Practical Organic chemistry 1 Determination of melting point Prepared by : Pshtiwan Ghareeb Ali Bsc. In Pharmacy Lab. Assisstant

Melting is the change from the highly ordered arrangement of particles in the crystalline lattice to the more random arrangement that characterizes a liquid (see Figures). Melting occurs when a temperature is reached at which the thermal energy of the particles is great enough to overcome the intracrystalline forces that hold them in position.

Physical properties, such as melting point, boiling point, and solubility, are largely determined by intermolecular forces 1 . L O N D O N AT T R A C T I V E F O R C E S ( O F T E N C A L L E D V A N D E R WA A L S F O R C E S ) 2 . D I P O L E - D I P O L E A T T R A C T I V E F O R C E S 3 . H Y D R O G E N- B O N D I N G 4 . I O N I C A T T R A C T I V E F O R C E S 5 . C O M P E T I N G I N T E R M O L E C U L A R F O R C E S A N D S O L U B I L I T Y For detail of each forces Please refer to theoretical Organic chemistry

Uses of M.P and it’s types 1- indication of purity 2-Identification of unknowns Although not always strictly true, it is considered that a sharp melting point rane <2 C between the first appearance of drops of liquid with in the sample to the disappearance of the last trace of solid constitutes good evidence for believing a substance to be pure. Conversely, a broad melting point, although strong evidence for lack of purity, can result if a pure substance decomposes on heating, thus introducing impurities. Darkening of the sample or evolution of a gas is an indication that this is occurring.

Measurement of melting point

Procedure

Requirements

Capillary sealing and taking the sample

Assembly of apparatus

Melting point processing