I. Experiment 5: Melting Point and Boiling Point Determination INTRODUCTION  Boiling point and melting point = physical properties  Help in identifying compounds  Help in differentiating organic from inorganic substances  Establishing purity  Requires overcoming intermolecular forces Boiling Point Def.  Temperature at which boiling occurs at a given pressure  Vapor pressure = atmospheric pressure  Temperature @ which liquid turns to gas Melting point Def.  Temperature at which solid turns to gas Impure solids and liquids  Melt over a wide range of temperature  Boil at lower temperature Factors affecting BP and MP 1) Molecular size (________) 2) Branching (________) 3) Polarity (________) 4) Molecular symmetry (________) 5) Intramolecular H-bonding (________) METHODOLOGY Melting point: Urea + Benzoic Acid Benzoic acid Boiling point: Hexane Experiment 4 Distillate (Ethanol – 95% AND 45%) RESULTS MP Benzoic acid: 116-142 Benzoic acid + Urea: 84-116 BP Hexane: 82 1 st distillate (simple): 84 2 nd distillate (fractional): 86 DISCUSSION Melting point  Mixture shrinks, slumps, soften  Mixture melts = enough heat applied to overcome interaction between molecules  Benzoic acid (pure) = High MP o Large molecular size o Higher # of carbons present  Benzoic acid + Urea = Wide range of MP o Presence of impurities o Vapor pressure lowering (Raoult’s law)