Analytical techniques
No description yet. This curated deck is ready for daily study.
Card preview (17)
How are compounds identified?
Mass spectrometry
How is a mass spectrometer used to identify compounds
• Used to determine the relative molecular mass of a compound • A molecular ion is formed when a molecule looses an electron • The molecular ion produces a molecular ion peak of the compound • The mass/charge of the molecular ion peak will be the same as the molecular mass of the compound
What is a high resolution mass spectrometer
Measure atomic and molecular masses extremely accurately
What is the use of high resolution spectrometers
useful for identifying compounds that appear to have the same Mr
What method is used to identify organic molecules
infrared spectrometry
How is infrared spectroscopy used to identify organic compounds
Infrared radiation is absorbed by the covalent bonds in the molecules, increasing their vibrational energy
What are the 2 principles about how bonds absorb frequencies
• Bonds between different atoms absorb different frequencies of IR radiation • Bonds in different places in a molecule absorb different frequencies too
How is wave number calculated
1/wavelength
What does an infrared spectrometer produce
• A graph that shows you what frequencies of radiation the molecules are absorbing to identify the functional groups
Where do the peaks on the IR spectra point?
Downwards
What do the peaks show
Where radiation is being absorbed
What does the fingerprint region identify?
Molecules
What will any impurities show in the fingerprint region
• Produce extra peaks
Describe how infrared radiation absorption is linked to Global warming
• Electromagnetic radiation emitted by the sun reaches the earth • The earth re-emits some of it as infrared radiation (heat) • Some of the greenhouse gases e.g CO2, methane and water vapour absorb this infrared radiation and re-emit it • This keeps us warm and it’s called the greenhouse effect • Burning fossil fuels and leaving waste in landfills causes a rise in green house gas concentration • More heat is being trapped and the earth gets warmer- Global warming
How can you distinguish between two structural formulas
Draw them out
In what instance can the Mr value in high resolution mass spectrometry not distinguish between two compounds
When the compounds have the same molecular formula
State why the precise relative atomic mass quoted in the table for the C12 isotope is exactly 12.00000
Carbon-12 is the standard/ reference value/isotope