M3

• PHYSICAL ANALYSIS

  • no change in chemical composition
  • determine physical properties
• SULBILITY

  • substance to be dissolve in solvent
  • should be homogeneous with substance of un-dissolved sample
  • miscible (liquid - liquid solvent) in a solvent should be homogeneous
• BOILING POINT

  • temp whose liquid turn to gas
  • stronger ion dipole interaction make it difficult to the gas phase more energy is needed to break them — higher boiling point
• Solubility Determination


  1. Prepare 100 mg of each sample in a test tube and label accordingly

  2. Add 5 mL of solvent

  3. Agitate

  4. Observe the solubility/miscibility
• Melting Point Determination


  1. Prepare powdered samples and place into capillary tubes

  2. Turn on the Automatic Melting Point Apparatus and set to the sample’s reference temperature

  3. Place capillary tube with sample in the heating furnace

  4. Wait until the machine alarms
• Boiling Point of Organic Compounds


  Temperature at which the vapor pressure of a liquid is equal to the external pressure
• Physical Property


  A characteristic of a substance not associated with a change in chemical composition
• Simple analysis of organic compounds

  • Solubility
  • Melting Point
  • Boiling Point
• The physical properties of a compound, such as melting point and boiling point, can provide useful information which can help in the identification of a sample or to establish its purity
• Functional groups with solubility properties

  • Carboxylic acids
  • Carboxylic acids with fewer than five carbon atoms are soluble in water and form solutions that give an acidic response (pH<7) when tested with litmus paper
• Amines (RNH2)


  • Soluble in water if they have fewer than five carbons and give a basic response (pH>7) with litmus paper
• Ketones, Aldehydes, Alcohols (RCOR, RCOH, ROH)


  • Soluble in water if they have fewer than five carbon atoms and form neutral solutions (pH=7)
• Solubility in NaOH


  1. Positive identification test for acids

  2. Carboxylic acid insoluble in pure water will be soluble in base due to the formation of sodium salt of the acid
• Solubility in HCl

  1. Positive identification test for bases

  2. Amines insoluble in pure water will be soluble in acid due to the formation of an ammonium chloride salt
• Melting Point


  • Temperature at which a solid melts and becomes a liquid
• Melting Point of Organic Compounds

  • Pure samples have sharp melting points, impure samples melt at lower temperatures and over a wider range, pure non-ionic crystalline organic compounds usually have a sharp and characteristic melting point, mixtures of impurities depress the melting point and increase the melting point range
• Boiling Point


  • Temperature at which the vapor pressure of a liquid is equal to the external pressure
• Boiling Point of Alcohols


  • Boiling point increases with the length of the hydrocarbon chain, alcohols have a higher boiling point than alkanes due to intermolecular bonding
• Straight chain compounds vs. branched compounds

  Straight chain compounds have large size, high polarizability, strong London dispersion forces, and high boiling points, while branched compounds have low polarizability, low boiling points