Spectroscopy Flashcards
1
Q
How would you explain fragmentation?
A
- During the use of a mass spectrometer some molecular ions break down into smaller pieces called ‘fragments’.
- These ‘fragments’ are actually called fragment ions.
2
Q
What happens when covalent bonds absorb IR radiation?
A
- These bonds naturally posses energy and ability to vibrate around the central point. This can increase when temperature has been increased.
- These same bonds can absorb IR radiation that makes the stretch and bend more.
3
Q
What does the amount a bond stretches/bends depend on?
A
- Mass of atoms in the bond - heavier atoms vibrate more slowly than lighter ones.
- Strength of the bonds - Stronger bonds vibrate faster than weaker bonds.
- Can only absorb radiation with the same frequency as natural frequency of bond, this is measured in wavenumbers.
4
Q
How does IR radiation affect greenhouse gases?
A
- IR radiation supplies molecules such as water vapour, carbon dioxide and methane with more energy to stretch and bend. These molecules eventually re-emit the energy as heat energy so it increase the temp. in the Earth’s atmosphere. This is the main cause of global warming.
5
Q
How is infrared spectroscopy applied?
A
- Remote sensors can monitor localised pollution by analysing IR spectra of vehicle emissions.
- IR-based breath-analysers pass beam of IR radiation through captured breath in sample chamber and detect IR absorbance in breath. Characteristic bonds in alcohol are detected. The more IR radiation absorbed, the higher the reading and more ethanol is in the breath.
6
Q
How do chemists identify functional groups?
A
- Elemental analysis - use of percentage composition data to determine empirical formula.
- Mass spectrometry - use of molecular ion peak from mass spectrum to determine molecular mass. Fragment ions cause peaks and help identify sections of a molecule.
- Infrared spectroscopy - use of absorption peak from infrared spectrum to identify bonds and functional groups present in molecule.
