PMT flashcards chapter 29

Cards (51)

  • What is chromatography?
    A family of separation techniques
  • What principle does chromatography depend on?
    Mixtures are separated when dissolved in a solvent
  • What is the mobile phase in chromatography?
    It carries the soluble components of the mixture
  • What relationship makes a sample move faster in chromatography?
    More soluble components move faster
  • What does the stationary phase do in chromatography?
    It holds back components attracted to it
  • What relationship makes a sample move slower in chromatography?
    More affinity for the stationary phase means slower movement
  • What kind of bonding often slows down a sample in chromatography?
    Often involves hydrogen bonding
  • How are substances separated by chromatography?
    Different affinities for mobile and stationary phases
  • Why do different substances show different Rf values?
    They have different polarities and bonding
  • What does TLC stand for?
    Thin Layer Chromatography
  • What is the stationary phase in TLC?
    Coated sheet of silica or alumina
  • What are the advantages of TLC over paper chromatography?
    • Runs faster
    • Smaller amounts can be separated
    • TLC plates are more robust than paper
  • How can you observe colourless spots in chromatography?
    Shine UV light or use a developing agent
  • How do you calculate the Rf value?
    Rf = distance moved by spot / distance moved by solvent front
  • What does Rf value stand for?
    Retention factor
  • How can you confirm the identity of a substance from its Rf value?
    Compare Rf value to accepted values
  • What is the stationary phase in gas-liquid chromatography?
    Powder coated with oil in a capillary tube
  • What is the mobile phase in gas-liquid chromatography?
    Carrier gas, inert like N2 or He
  • What do you measure in gas-liquid chromatography?
    Retention time of components
  • What are the advantages of GLC?
    Very sensitive to minute traces of substances
  • What are GLC’s uses?
    Testing blood and urine for drugs
  • How can you use GC or GCMS to identify substances?
    Match retention time to known substances
  • How does GCMS work?
    Run GC, record retention time, then use MS
  • How do you test for alkenes and what is the result?
    Shake with bromine water; decolourised
  • How do you test for haloalkanes and what is the result?
    Add NaOH, acidify, add AgNO3; precipitate forms
  • How do you test for alcohols and what is the result?
    Add acidified K2Cr2O7; orange to green change
  • How do you test for aldehydes and what are the results?
    Warm with Fehling’s; brick red ppt forms
  • How do you test for carboxylic acids and what is the result?
    Add Na2CO3; CO2 gas given off
  • How do you test for phenols?
    Neutralisation reaction with NaOH
  • How do you test for carbonyl compounds?
    React with 2,4-DNP; orange precipitate forms
  • What does NMR stand for?
    Nuclear Magnetic Resonance
  • What are the basic principles of NMR?
    It uses magnetic fields and radio waves to analyze nuclei
  • How does NMR determine the structure of complex molecules?
    By placing them in a magnetic field and applying EM waves
  • What happens to nuclei in NMR when the right frequency of radio waves is absorbed?
    The nuclei flip from parallel to anti-parallel
  • What is one use of NMR?
    MRI scans
  • What kind of nuclei does NMR work with?
    Nuclei with an uneven number of nucleons
  • What do the following indicate for 13C NMR: Number of signals, Chemical shift, Area under peak, Splitting?
    • Number of signals: One for each carbon environment
    • Chemical shift: Greater indicates different environments
    • Area under peak: Proportional to number of carbon atoms
    • Splitting: Not applicable for 13C NMR
  • Why is it easier to get a spectrum of 1H NMR than 13C NMR?
    1H is more abundant than 13C
  • What peaks would you expect to see for H NMR on a low resolution spectrum?
    One peak for each set of inequivalent H atoms
  • What does the area under the peak represent for H NMR?
    It is proportional to the number of 1H atoms