PMT flashcards chapter 29

• 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