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Stage 2 Chemistry > Topic 1 - Monitoring the Environment > Flashcards

Topic 1 - Monitoring the Environment Flashcards

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1
Q

Name the common greenhouse gases.

A

Carbon dioxide: CO2
Water vapour: H2O
Methane: CH4
Nitrous oxide: N2O
Ozone: O*

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2
Q

What is thin layer chromatography (TLC)?

A

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.

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3
Q

How is atomic absorbance spectroscopy (AAS) structured?

A

Hollow cathode lamp, flame, and monochromator.

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4
Q

How does the hollow cathode lamp work?

A

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.

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5
Q

What is the flame used in AAS?

A

The characteristic radiation is directed towards the flame, allowing atoms in the flame to absorb unwanted energies.

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6
Q

How does the monochromator work?

A

The monochromator is specific to one distinct frequency, allowing the desired one to be analysed.

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7
Q

What do catalytic converters do?

A

Catalytic converters convert harmful into less harmful compounds. However, majority of the time, more greenhouse gases are produced.

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8
Q

Catalytic converter equation for carbon monoxide.

A

2CO(g) + O2(g) —> 2CO2(g)

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9
Q

Catalytic converter equation for nitrogen oxide.

A

2CO(s) + 2NO(g) —> N2(g) + 2CO2 (g)

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10
Q

Catalytic converter equation for any unburnt hydrocarbons from incomplete combustion.

A

C3H8(g) + 5O2(g) —> 3CO2(g) + 4H2O(l)

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11
Q

How is photochemical smog formed?

A

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.

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12
Q

What are polar bonds?

A

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.

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13
Q

What is retention time?

A

The amount of time taken for a compound to exit the column, based on polarity.

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14
Q

How do you calculate retention factor?

A

Rf= distance from origin to component / distance from origin to solvent front

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15
Q

What does a low and a high Rf mean?

A

Low Rf - component did not move a lot
High Rf - component travelled a lot

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16
Q

What is extrapolation?

A

The unknown value is larger than the calibration curve.

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17
Q

What is an emission spectra?

A

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.

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18
Q

What is an absorption spectra?

A

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.

19
Q

How is relative polarity determined?

A

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

20
Q

What are the conditions for photochemical smog?

A
  • high concentration of pollutants
  • sunlight
  • still conditions
  • temperature inversion
21
Q

How does the greenhouse effect maintain a steady temperature in the Earth’s atmosphere?

A

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.

22
Q

Describe the enhanced greenhouse effect.

A

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).

23
Q

What are the properties of the natural greenhouse effect?

A
  • 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
24
Q

What enables molecules to absorb infrared radiation?

A

Only molecules with polar bonds can absorb IR.

25
Q

Explain why a molecule (e.g. CO2) is non-polar, even though it has polar bonds.

A

CO2 is a linear molecule. There are no two distinct regions of charge as the dipoles cancel each other out to yield a molecule with no net dipole.

26
Q

Write equations to show the ionisation of carbonic acid.

A

Acids are proton donors, meaning hydronium ions are formed from ionisation. Carbonic acid (H2CO3) is deprotonated in the two step ionisation process:
H2CO3 + H2O —> HCO3- + H3O+
HCO3- + H2O —> CO3(2-) + H3O+

27
Q

Formulas for calculating pH and pOH.

A

pH = -log(H+)
pOH = -log(OH-)
(H+) = 10^(-pH)
(OH-) = 10^(-pOH)
pH + pOH = 14

28
Q

Primary VS secondary pollutants.

A

PRIMARY - directly emitted into the atmosphere (NO2 and CO2)
SECONDARY - produced within the atmosphere by chemical reactions (O* and H2SO4)

29
Q

What is a limiting reagent?

A

Reactants are not always present in exact stoichiometric ratios. Typically, one reagent will be present in excess. The reagent that is completely consumed within a reaction is called the limiting reagent.

30
Q

Describe the three different types of titrations.

A

NORMAL - do not always work due to issues with the unknown substance being too volatile, insoluble or slow to react
A + B —> C + D
BACK - two reactions, linked by an excess reagent
A + B —> C + D B + E —> F + G
INDIRECT - two reactions, linked by a common reagent
A + B —> C + D D + E —> F + G

31
Q

How does atomic absorption function?

A

Electrons occupy the lowest energy level known as the ground state. These electrons can absorb photons of discrete amounts of energy (heat, light or electricity) which promotes electrons to a higher energy level (subshell), known as the excited state. This excited state is unstable, causing the electrons to return to the ground state via the loss of additional energy which is emitted as photons of light.

32
Q

What do calibration curves for AAS show?

A

Calibration curves are graphs with the ability to determine absorbance or concentration of an unknown substance. Absorbance is directly proportional to concentration.

33
Q

How is random error and systematic error shown in calibration curves?

A

RANDOM ERROR - scattered points
SYSTEMATIC ERROR - entire graph moved upwards or downwards; does not pass through origin

34
Q

Method for finding the concentration of an unknown substance using AAS.

A
  1. Standard solutions of increasing known concentrations are prepared for the metal under investigation.
  2. Distilled water is also prepared and introduced along with the known standards.
  3. The absorbance is measured using AAS.
  4. Data is gathered and plotted on a graph, with a line of best fit.
  5. The absorbance of the unknown can be measured and interpolated to find the concentration.
35
Q

What is chromatography and where is it used?

A

Chromatography is the separation and purification of components of a mixture based on their polarity. It is used in a range of applications including forensic investigations, quality control and environmental monitoring.

36
Q

Chromatography normal phase VS reverse phase.

A

NORMAL - polar S.P. and non-polar M.P.
REVERSE - non-polar S.P. and polar M.P.

37
Q

What are some effects of global warming?

A
  • erratic weather patterns
  • increased severity and frequency of natural phenomena
  • agricultural cropping pattern changes
  • altered animal migration patterns
  • melting ice, glaciers and permafrost
  • rising sea levels
38
Q

What are some anthropogenic sources of increased greenhouse gases?

A
  • burning of fossil fuels (CO2)
  • clearing of rainforests (CO2)
  • agricultural activity (CH4)
  • landfill (CH4)
  • fertilisers (N2O)
  • internal combustion engines (N2O)
  • chlorofluorocarbons (CFCs)
  • water vapour (H2O)
39
Q

State and explain the equation that demonstrates ocean acidification.

A

Human activity contributes to rising CO2 emissions. Oceans absorb this CO2 from the atmosphere, forming carbonic acid in the equilibrium reaction below:
CO2 (g) + H2O (l) <—> H2CO3 (aq)
Too much dissolved CO2 can harm marine ecosystems and organisms.

40
Q

How does ocean acidification impact the environment?

A

Calcium carbonate is the main composer of sea shells, coral, mollusc and crabs. Ocean organisms build their habitats from calcium ions and carbonate ions in the sea:
Ca^(2+) + CO2^(2-) —> CaCO3
As oceans absorb the additional CO2 in the atmosphere, produced anthropogenically, the pH of the ocean decreases. This means that the concentration of protons (H+) increases, causing the dissolution of the solid calcium carbonate:
CaCO3 + 2H+ —> CO2 + H2O + Ca2+
This weakens the habitats of many marine organisms, whilst making it harder for them to build these habitats.

41
Q

What is a net ionic equation?

A

Only depicts the ions or molecules that are actively involved in the reaction.

42
Q

VSEPR Theory: Why is the molecule that shape?

A

Around the central ____ atom, there are ____ single/double/triple bonds and ____ non-bonded electron pairs, creating ____ regions of electron density. These position themselves as far apart as possible around the central atom to minimise repulsion. Therefore, a ____ shape is produced.

43
Q

Stoichiometric conversions.

A

DRAW CONVERSION CHART

44
Q

What are the effects of photochemical smog?

A
  • high levels of NO2 consumption can cause health complications, specifically respiratory issues, and can lead to decreasing crop yield
  • ozone is an unstable gas, meaning a small amount of energy will lead to the dissociation of the oxygen radical
  • ozone negatively impacts human health, specifically respiratory systems
  • plant life is also vastly effected as stomas close in response to ozone, meaning photosynthesis and hydration are prevented (stunting plant growth)
  • rubber and plastics are also damaged by ozone as polymer chains are broken at carbon-carbon double bonds

Stage 2 Chemistry (4 decks)

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