Topic 1 - Monitoring the Environment Flashcards
Name the common greenhouse gases.
Carbon dioxide: CO2
Water vapour: H2O
Methane: CH4
Nitrous oxide: N2O
Ozone: O*
What is thin layer chromatography (TLC)?
Glass/aluminium/plastic plate coated with a layer of absorbant (silica), known as the stationary phase. The origin and sample are placed on the plate. The plate is then dipped in a mobile phase solvent, and the components separate. This does not gain quantitative polarity values, only relative polarity assessments.
How is atomic absorbance spectroscopy (AAS) structured?
Hollow cathode lamp, flame, and monochromator.
How does the hollow cathode lamp work?
The hollow cathode lamp is composed of the metal to be determined, emits wavelengths of light at the characteristic frequency of the metal to be analysed, to excite it.
What is the flame used in AAS?
The characteristic radiation is directed towards the flame, allowing atoms in the flame to absorb unwanted energies.
How does the monochromator work?
The monochromator is specific to one distinct frequency, allowing the desired one to be analysed.
What do catalytic converters do?
Catalytic converters convert harmful into less harmful compounds. However, majority of the time, more greenhouse gases are produced.
Catalytic converter equation for carbon monoxide.
2CO(g) + O2(g) —> 2CO2(g)
Catalytic converter equation for nitrogen oxide.
2CO(s) + 2NO(g) —> N2(g) + 2CO2 (g)
Catalytic converter equation for any unburnt hydrocarbons from incomplete combustion.
C3H8(g) + 5O2(g) —> 3CO2(g) + 4H2O(l)
How is photochemical smog formed?
Gaseous nitrogen (N2) is required to produce the nitrogen dioxide in photochemical smog. The triple bond leads to an incredibly stable structure, which can only be broken to form nitric oxide when subjected to high energy: N2(g) + O2(g) –high energy–> 2NO(g) This nitric oxide can react with further oxygen in the atmosphere to form nitrogen dioxide: 2NO(g) + O2(g) —> 2NO2(g) Nitrogen dioxide can undergo a further photochemical decomposition reaction (initiated by light): NO2(g) –UV–> NO(g) +O(g) These highly reactive oxygen radicals formed (oxygen with one unpaired electron) can then bond with atmospheric oxygen to produce ozone: O(g) +O2(g) —> O3(g) The ozone and nitrogen oxides act as pollutants within the atmosphere, to form photochemical smog.
What are polar bonds?
Polar bonds are covalent bonds between atoms with different electronegativities, leading to unequal sharing of valence electrons. This causes the formation of a positive and negative dipole.
What is retention time?
The amount of time taken for a compound to exit the column, based on polarity.
How do you calculate retention factor?
Rf= distance from origin to component / distance from origin to solvent front
What does a low and a high Rf mean?
Low Rf - component did not move a lot
High Rf - component travelled a lot
What is extrapolation?
The unknown value is larger than the calibration curve.
What is an emission spectra?
Emission spectra occurs when light is emitted by a species once relaxation occurs from an excited state to a ground state. This is shown with a dark background and bright coloured lines.
What is an absorption spectra?
Absorption spectra occurs when light is absorbed by a species for excitation to occur from a ground state to an excited state. This is shown with a coloured background and dark coloured lines.
How is relative polarity determined?
POLAR GROUPS - the more polar function groups there are, the higher the overall polarity of the molecule will be
SIZE - larger molecules are less polar, due to atomic radii
What are the conditions for photochemical smog?
- high concentration of pollutants
- sunlight
- still conditions
- temperature inversion
How does the greenhouse effect maintain a steady temperature in the Earth’s atmosphere?
Visible and UV radiation from the sun passes through the atmosphere to the Earth’s atmosphere. This solar radiation is either reflected back to space, absorbed by the atmosphere or land and ocean surfaces, or re-emitted as infrared radiation. Greenhouse gases in the lower atmosphere absorb some of this re-radiated energy (IR) which is then transferred between greenhouse gases, directed back to the Earth’s surface, and lost to space. Therefore, maintaining the thermal balance.
Describe the enhanced greenhouse effect.
Increased levels of greenhouse gases in the atmosphere disrupt the thermal balance. More thermal IR radiation being absorbed by greenhouse gases means less escaping the Earth’s atmosphere, causing an increase in the overall temperature of the planet (global warming).
What are the properties of the natural greenhouse effect?
- natural and essential for life to be able to survive on Earth as the absorbed thermal IR radiation maintains a steady atmospheric temperature
- average surface temperature without is negative 17 degrees Celsius
- average surface temperature with is 15 degrees Celsius
What enables molecules to absorb infrared radiation?
Only molecules with polar bonds can absorb IR.