WM 2

• Reflux

  1. Technique used to heat volatile liquids without losing them to the atmosphere

  2. Involves setting up a reflux setup where volatile compounds evaporate, condense against the condenser, and drip back down

  3. Commonly used in organic chemistry for flammable liquids

  4. Heating is done under a water bath or using an electric heating mantle to avoid direct flame
• Distillation

  1. Used to separate substances with different boiling points

  2. Involves gently heating a mixture to specific boiling points to allow separation

  3. Substances with lower boiling points evaporate first and are collected in a separate flask

  4. Useful for extracting chemicals before they react further
• Filtration


  Used to separate solids from liquids, often done through vacuum filtration
• Separation

  Technique to remove impurities dissolved in water
• Distillation

  Useful for extracting a chemical before it reacts further, e.g., with primary alcohols
• Redistillation


  Used to purify a volatile substance further by separating impurities through distillation
• Purification

  Adding anhydrous calcium chloride to remove any remaining water from the organic layer
• Vacuum filtration

  1. Connect to a vacuum equipment or a tap with a vacuum valve attached to create a vacuum

  2. Place paper discs inside the funnel, wet them slightly for a good seal, pour the reaction mixture through the top of the funnel, switch on the vacuum line to draw the liquid through and leave the solid powder stuck in the top of the funnel
• Recrystallization

  Add hot solvent to dissolve impure solid, allow to cool slowly to form crystals, filter the solid purified crystals, wash with cold solvent, dry off
• Testing purity of solid product

  Add a sample of the solid product into a capillary tube, place it into a heating element in a melting point apparatus
• Choosing the right solvent is crucial in recrystallization to ensure the impure solid dissolves fully in hot solvent but is virtually insoluble when cold
• Testing the purity of the solid product can be done by measuring its melting point
• Vacuum filtration creates reduced pressure to pull the liquid through and leave the solid behind
• Recrystallization

  A method to purify solids by dissolving impure solid in hot solvent, allowing it to cool to form crystals, filtering, washing with cold solvent, and drying
• If a substance contains many impurities, the melting point will be lower than the data book value and the temperature range will be larger
• Thin layer chromatography (TLC)

  Separates and identifies compounds using a stationary phase of silica or alumina mounted on a glass or metal plate, drops of mixture are added onto a pencil line drawn on the plate, a glass lid is placed on top to prevent solvent evaporation, the plate is placed into a liquid solvent as the mobile phase, the solvent moves up the stationary phase carrying the compounds, spots of chemicals may dissolve differently and deposit at different positions on the chromatogram, compounds can be identified by measuring the positions of the spots in reference to the solvent line
• Fluorescent dyes can be added to silica or alumina in TLC to visualize colorless spots under a UV lamp
• If a substance has a sharp and narrow temperature range, it indicates fewer impurities in the sample
• Melting point determination

  Add a sample of the solid product into a capillary tube, place it into a heating element in a melting point apparatus, slowly increase the temperature until the substance starts to melt, observe the temperature range from when the solid starts to melt to when it fully melts, compare the melting point against data book values to check for impurities
• Colorless compounds can be visualized using iodine or fluorescent dyes and UV lights in TLC
• Column chromatography is ideal for separating and purifying larger quantities of a mixture
• RF values can be calculated by taking the distance traveled by the spot divided by the distance traveled by the solvent
• Compounds in the mixture move through the column at different rates, allowing for separation and collection of different bands
• Fluorescent die visualization

  Using a UV lamp to see the fluorescent die, colorless spots on the chromatogram block the glow, drawing circles around these spots
• Measuring spots relative to the solvent front is done using an RF value
• Iodine visualization

  Placing chromatogram in a sealed jar with iodine crystals, iodine vapor migrates through the jar and dyes the chemicals on the plate purple, iodine vapor acts as a locating agent
• Number of spots on the plate indicates the number of chemicals in the mixture
• RF values are fixed for each chemical under specific conditions
• In column chromatography, a glass column is packed with silica or alumina as the stationary phase, and the mixture and solvent (mobile phase) are run through continuously
• Identifying individual chemicals using infrared spectroscopy

  IR spectroscopy uses infrared radiation to increase vibrational energy of covalent bonds in the sample, frequency of absorbed radiation depends on atoms and position of the bond in the molecule
• Mass spectrometry helps identify the compound's relative molecular mass
• The M plus Peak in mass spectrometry is the molecular ion peak, representing the relative molecular mass of the molecule
• Separating chemicals using chromatography

  Collecting bands in separate beakers to obtain pure chemicals
• Infrared spectrum can identify functional groups present in a substance
• Most fragments in mass spectrometry have a charge of plus one
• An M plus1 Peak in mass spectrometry indicates a molecule with an isotope present
• Specific peak numbers in mass spectra can provide information about particular fragments, e.g., Peaks at 17 for O plus, Peaks at 15 for ch3 plus, Peaks at 28 for carbon groups C bond O plus
• Fragmentation patterns in mass spectrometry can be used to identify molecules with the same constituent atoms
• Fragmentation in mass spectrometry

  Molecules break up when bombarded with high energy electrons, producing positive fragments and radicals. Only the positive fragments are detected in the mass spectrometer
• Isotope in a molecule

  • Carbon 13 atom in an organic molecule increases the mass by one, showing up as a tiny peak called an n plus 1 Peak