Environmental Inorganic Chemistry

Front 1

What are the terrestial planets?

Back 1

The planets closest to the sun

Front 2

What are terrestial planets formed from?

Back 2

High melting point elements e.g. iron, nickel, silicon, as they can exist as dust and form planets.

Front 3

What does being further away from the protosun result in for other planets in terms of their composition?

Back 3

Explains the existence of the gas planets, away from the sun it is cool enough for lighter compounds such as ammonia and water to exist.

Front 4

What is the most abundant element in the earth's crust? What is it in the whole earth?

Back 4

In the crust the most abundant element is oxygen (46%), however over the entirety of the earth it is iron (35%)

Front 5

What ais the main composition of the inner core, mantle and crust of earth?

Back 5

The inner core is mainly composed of iron and nickel, whilst the mantle and crust contain higher levels of silicon and oxygen

Front 6

What happened in the iron catastrophe?

Back 6

As a consequence of heating from compression of planetesimals to form earth, and radioactive decay, the temperature of earth was raised above 2000 degrees. This resulted in molten iron falling towards the centre of the earth, whilst lighter elements moved towards the crust. The liquids released trapped volatile molecules as gas to create the atmosphere.

Front 7

What is the lithosphere? What is it composed of?

Back 7

The crust and upper mantle of the earth's surface. Composed of rocks that undergo the rock cycle.

Front 8

Outline the rock cycle

Back 8

Igneous rock (crystalisd magma) converted by physical and chemical processes into sedimentry rock. Heat and pressure applied to transform into metamorphic rock, which melts and then cools to give igneous rock again.

Front 9

What are minerals?

Back 9

Minerals are naturally occuring inorganic solids with a define chemical composition and crystal structure. Rocks are aggregates of minerals.

Front 10

What is over 80% of the earths crust composed of?

Back 10

Al, Si and O

Front 11

How are silicate minerals first produced? What does their chemical composition depend on?

Back 11

Fractional crystalisation from magma, products depend on magma chemical composition, temperature and pressure

Front 12

What is igneous differentiation?

Back 12

As magma cools, silicates that are stable at a high temperature crysalise out first changing the chemical composition of the remaining liquid. Cooling produces a new mineral with a different composition to the original.

Front 13

Outline the process of discontinuous differentiation?

Back 13

At high temperatures minerals containing simple silicate anions (orthosilicates) crystalise first from magma. As O in magma is depleted silicates with lower Si:O ratios crystalise out. These can condense to form di-silicates and cyclosilicates, as well as pyroxenes and amphiboles. Minerals are produced with silicate layers e.g. soapstone, before the final product; 3D silicate quartz frameworks.

Front 14

At high temps the orthosilicates formed are rich in Mg, Fe and Ca. Common to find (Mg,Fe)-olivines

Back 14

A continuous series between two extreme structures Mg2SiO4 and Fe2SiO4

Front 15

What is the formula for common orthosilicates to be found during discontinuous differentiation crystalisation process of magma?

Back 15

X3Y2(SiO4)3
Where X = Mg2+, Fe2+ and Ca 2+
And Y = Al3+, Fe3+ and Cr3+

Front 16

What happens as the amount of oxygen in the magma gets depleted? Show an example

Back 16

Silicates with lower Si:O ratios are crystalised out through the merging of silicate tetrahedra to form di-silicates.

2[SiO4]4- ---> [Si2O7]6- + O2-

Front 17

Why are disilicates rare in reality?

Back 17

As they rapidly condense to form cyclo-silicates e.g. beryl (Be3Al2Si6O18)

Front 18

Cyclosiliciates are one form of meta silicate, another form is pyroxenes. What is a pyroxene composed of and what is its siochiometric formula?

Back 18

A pyroxene contains polymeric anions composed of single chains of silica tetrahedra

XYSi2O6

Front 19

What is an amphibole?

Back 19

At lower temperatures double linked chains can form between silica tetrahedra anions forming an amphibole.General formula X2Y5(Si8O22)(OH2)

Front 20

What is the final product of the process where silica tetrahedra polymerise as the magma cools?

Back 20

A 3D silicate framework typified by quartz (SiO2)

Front 21

Summarise the discontinuous series from high to low temperature of silicate crystalisation from magma, giving both name of silicate and structure

Back 21

Olivine [SiO4]4- units, Pyroxene (single chain), Amphibole (double chain), Soapstone (sheets), quartz (framework)

Front 22

Outline the process of contuinous differentiation

Back 22

The third most common element in the crust is Al which can substitute for Si. Forms 'feldspar' structures that are similar to quartz and make up around 60% of the crust.

General form XAl2Si2O8

Front 23

Which metal ions are most common at high and low temps respectively in magma?

Back 23

At high T rich in Fe2+, Ca2+, Mg2+

At low T rich in Na+, K+

Front 24

Summarise the series of continuous differentiation of crystalisation from magma from a high T to low T

Back 24

Ca rich feldspar (CaAl2Si2O8)

Na rich feldspar (NaAl2Si2O8)

K rich feldspar (KAl2Si2O8)

Front 25

What are two forms of chemical weathering mechanisms?

Back 25

Dissolution/hydrolysis

Oxidation

Front 26

Which silicates are most susceptible to dissolution? How can this be related to temperature of formation to give a general rule?

Back 26

Orthosilicates, the less polymerised silicates wil be more ionic and hence more water soluble. Higher temperature of formation of mineral, more ionic, more easily weathered by dissolution.

Front 27

Which minerals are susceptible to chemical weathering by oxidation?

Back 27

Those with metal ions that can undergo oxidation e.g. olivines such as Fe2SiO4, as it contains Fe(II)

Front 28

What accelerates the oxidation process?

Back 28

The presence of water

Front 29

What is the composition of water on the Earth's surface?

What is the average surface temp?

What is the composition of Earth's atmosphere?

Back 29

71% water

14 degrees

21% O 78% N

Front 30

Explain how N2 became the major component of the atmosphere

Back 30

Earth's formation was from the condensing of planetisimals, which warmed and melted. This lead to out-gassing of trapped and frozen gasses such as CO2, water vapour and N2. All H2 and He escaped into space. As earth cooled, the water condensed out of the atmosphere as clouds, rain and oceans. CO2 condensed into 'rain water' forming limestone. This left N2 as the main component

Front 31

What is the source of oxygen in the atmosphere?

Back 31

All from photosynthesis, biological systems are the source of all earth's oxygen

Front 32

Outline the evolution of earth's oxygen in the atmosphere

Back 32

Originally no O2 produced, then produced but absorbed in seabed rock and oceans, starts to gas out of oceans but absorbed by land surfaces and formatio of ozone layer, O2 sinks filled and gas accumulates

Front 33

Briefly outline the photocatalysed formation of the ozone layer. How does this cause a temperature inversion?

Back 33

O2 + hv --> 2O (photolysis requires λ <241nm)

O + O2 + M ---> O3 + M*

M is a third body (usually N2) that removes energy generated in the reaction

Temperature inversion to due absorption of UV light by oxygen

Front 34

How is ozone destructed by photolysis?

Back 34

O3 + hv ---> O2 + O (requires photons with λ<320nm)

O3 + O --> 2O2

Front 35

It was seen that O3 + O --> 2O2 was too slow to produce the O3 concentrations seen in the real atmosphere, how does N2O speed up the process?

Back 35

N2O + O --> 2NO' (radical formation)

Catalytic cycle:

NO' + O3 --> NO2' + O2

NO2' + O --> NO' + O2

Net reaction: O3 + O --> 2O2

Front 36

What can be noted about the regeneration of NO'?

Back 36

It can participate in the cycle repeatedly, it will only be removed by reaction with a non-oxygen species

Front 37

What is the full Champman cycle?

Back 37

The cycle of the formation and destruction of the ozone layer to produced a steady state concentration of O2 in the atmosphere.

I.e. the steps described above combined including the catalytic activity of NO'

Front 38

Define 'anthropogenic'

Back 38

Effects or processes that are derived form human activities

Front 39

How do CFC's (e.g. CCl3F) lead to ozone layer depletion?

Back 39

Very inert so can travel into stratosphere.

CClF3 + hv --> CCl2F' + Cl'

Cl' + O3 --> ClO' + O2

ClO' + O --> Cl' + O2

Front 40

CFC catalystic process results in regeneration of Cl' - how can the catalytic process above be terminated?

Back 40

1) ClO' + NO2' + M --> ClONO2 + M

2) Cl' + CH4 --> HCl + CH3' Ch3' can react with O2 to eventually form CO2

Front 41

Why did a hole start to form in the ozone layer above the arctic in spring?

Back 41

No sunlight, temperature < -80 degrees resulting in the formation of HNO3 and Cl2. The nitric acid removes source of NO2 for termination reaction reactivating Cl2 into 2Cl'. This results in a catalytic process that overall gives 2O3 --> 3O2.

Front 42

What are the two main causes of smog

Back 42

Hydrocarbon fuel combustion and sulphur impurities in coal

Front 43

Show how both efficient and inefficient hydrocarbon fuel combustion results in air pollution through particulate smog

Back 43

Efficient: 4(CH) + 5O2 --> 4CO2 + 2H2O

Inefficient: 4CH + 3 O2 --> 4CO + 2H2O

Very inefficient: 4CH + O2 --> 4C(s) + 2H2O

Solid Carbon particles in smog

Front 44

Explain how sulphorous smog is produced from impurities in coal

Back 44

S+ O2 --> SO2 which is a irritant/toxic gas

In damp conditions: SO2 + H2O --> HSO3- + H+

With trace amounts of Fe catalyst:

2HSO3- + O2 --> 2H+ + SO42-

basically leads to H1SO4 formation

Front 45

What is the proble with H2SO4 in the atmosphere?

Back 45

It is hygroscopic, meaning it absorbs water from damp air and thickens the smog

Front 46

Summarise the chemistry of sulphurous smogs

Back 46

Inefficient combustion + oxidation of sulphur based impurities = thick smog containing carbon particles, CO2, CO and H2SO4.

Now black smoke emission banned, forced conversion to smokeless fuel

Front 47

Summarise how is photochemical smog produced

Back 47

Internal combustion engine + volatile organic compounds (VOC's) in sunlight = nitrogen oxides + ozone + peroxynitriles and nitric acid

Front 48

What happens in the internal combustion of an engine?

Back 48

High temperatures of engine leads to

N2 + O2 --> NO2 and 2NO + O2 --> NO2

NO2 can absorb visible light, same reaction occurs as in stratosphere.

NO2 + hv --> NO + O

O + O2 + M --> O3 + M

NO + O3 --> NO2 + O2

Null cycle, cancels out

Front 49

What is a consequence of incomplete combustion of petrol?

Back 49

VOC's such as CH4 react with hydroxyl radical HO' to create new cycle of radical reactions.

HO' regenrated and can recycle

NO2 is regenerated without depletion of O3, no longer a null cycle so ozone levels increase

Front 50

What is a consequence of the HO' radical catalytic cycle that leads to even more NO2 production without O3 depletion?

Back 50

The formation of ketone and aldehyde radicals that can form peroxyl radicals which react with NO to form NO2

Front 51

What is a peroxyacetyl nitrate (PAN)?

Back 51

A toxic compound formed from reaction of ester radicals and NO2.

Front 52

Why does PAN, HNO3, H2O2 generation fall at night?

Back 52

Because depends on HO' radical which is generated by sunlight

Front 53

What is the aim of a catalytic converter?

Back 53

To reduce Nox and VOC emissions

Front 54

What are the main sections of catalytic converter?

Back 54

A Pt/Rh catalyst on a ceramic honeycomb suport
A reduction chamber
An oxidation chamber

Front 55

What ocurs in the reduction chamber of a catalytic converter?

Back 55

NOx removed by Rh catalysed reduction process using unburnt hydrocarbons as reducing agents.

NO + CnHn+2 --> N2 + CO + H2O

Front 56

What ocurs in the oxidation chamber of a catalytic converter?

Back 56

Unburnt VOCs removed through air injection and oxidation using Pt catalyst

CH4 + 2O2 --> CO2 + H2O

Front 57

What are the problems with present technology in terms of catalytic converters?

Back 57

Fuel contains suplphur compounds oxidised to SO2 in engine, in converter 2SO2 --> H2S

Catalyst only reaches high efficiency at 300 degrees. 80% of a modern car's emissions are in the first few mins of starting

Front 58

What is a biogeochemical cycle and where does the energy come from to drive it?

Back 58

A cycle where biological, chemical and geological processes are all involved, and is driven by the internal heat energy of the earth and more importantly, solar energy

Front 59

What are the two carbon cycles the global carbon cycle can be divided to? Which occurs at a faster rate?

Back 59

The geological carbon cycle slow) and biological carbon cycle (fast)

Front 60

Outline what happens in the geological carbon cycle

Back 60

Atmospheric CO2 and limestone caCO3 dissolve in rainwater and get carried into the oceans, where C is mainly found as HCO3-. It precipitates out forming carbonate sedimentry layers on the sea floor, as the Earth's plates move the sediments are subducted beneathe the crust, and decompose into CO2 gas which is emmitted into the atmosphere by volcanicn eruptions.

Front 61

Explain the role of CO2 in the geochemical carbon cycle

Back 61

Normal rain water acidic due to dissolved CO2. This weather carbonate rocks found in streams and rivers, reuslting in high Ca2+ and HCO3- concentrations. In combination with water:

CO2 + H2O + CaCO3 --> Ca2+ + 2HCO3-

large amounts of atmospheric CO2 can dissolve in natural water with little pH change. Rivers oceans etc can act as CO2 sink

Front 62

Outline the biological carbon cycle

Back 62

CO2 + H2O + hv --> [CH2O] + O2 photosynthesis acts as a carbon sink

[CH2O] + O2 --> CO2 + H2O respiration acts as carbon source

Front 63

What is the major anthropogenic contribution to the carbon cycle?

Back 63

Largest contribution is CO2. Mainly from burning fossil fuels, cement manufacture ( CaCO3 heat --> CO2 + CaO), and deforestation decreasing photosynthetic carbon sinks and burnt wood releasing CO2

Front 64

What other major anthropogenic contribution to the carbon cycle is there?

Back 64

Methane CH4 from agriculture such as rice paddies and cows

Front 65

What is a result of half of all anthropogenic CO2 being absorbed by the ocean?

Back 65

Despite the action of the bicarbonate/carbonate buffer, the ocean has acidified by 0.1 pH

Front 66

Explain why increased CO2 will affect coral and shelled sea organisms that use CaCO3 as building material

Back 66

The equilibirum exists that:

CaCO3 + CO2 + H2O --> Ca2+ + 2HCO3-

Increasing CO2 shifts equilibrium right and therefore depleting CaCO3 resources

Front 67

What is the solar constant?

Back 67

The amount of solar energy received per unit area on the outer surface of the Earth's atmosphere

Front 68

What is albedo a mesaure of?

Back 68

It is a unitless measurement of a surface's reflectivity. It is the ratio of diffusely reflected electromagnetic radiation to incident radiation

Front 69

What is the Earth's energy input?

Back 69

Due to Earth radiating from its entire surface, divide solar constant by 4(pi)r^2 (area of sphere), then account for its albedo, a.
S = S(initial)/4 * (1-a) = 240Wm^-2

Front 70

How is energy lost from earth?

Back 70

Black body radiation where:

E=k(Te)^4

Te is the temperature of the Earth

Front 71

Since Earth's temperature is mainted at a pretty constant level, what can be deduced about earth's energy output?

Back 71

Energy loss from earth = solar energy input

k(Te)^4 = S(initial)/4 * (1-a)

Front 72

Using the equation k(Te)^4 = S(initial)/4 * (1-a) can calculate temperature of the earth to be 255K, however in reality it is 288K, what accounts for this difference?

Back 72

The green house effect

Front 73

Outline the greenhouse effect

Back 73

Most of atmosphere is composed of homo dinuclear gasses such as O2 which are transparent to visible and IR radiation, however other gasses such as CO2 and H2O are able to absorbs IR radiation due to having a permanent dipole moment, trapping the radiation and heating the earth.

Front 74

Explain why Mars is cooler than earth and Venus has much higher temperatures

Back 74

Mars is much smaller than Earth and has a lower gravity, so has a very thin atmosphere and greenhouse effect does not occur. Venus has no water to act as a sink for CO2 and therefore has more CO2 in atmosphere so larger greenhouse effect.

Front 75

What can be noted about CH4 greenhouse activity?

Back 75

Mass by mass it will have x72 the warming effect of CO2 over a 20 year period

Front 76

How does a decrease in the C13:C12 ratio show an increase in [CO2] is from human activity?

Back 76

Plants have a slight metabolic preference for C12 as C12-C12 bonds easier to break. Their enzymes decrease C13:C12 ratios in plant material. Burning old biological sources such as oil and coal releases more C12 decreasing ratio in atmosphere

Front 77

What is Nitrogen fixation?

Back 77

Conversion of dinitrogen into nitrogen derivatives that can be biologically processed e.g. nitrite ions

Front 78

Nitrogen fixation removes N2 from the atmosphere, but for it to be a cycle, N2 levels are in theory constant. Explain

Back 78

Denitrification occurs, in low oxygen conditions in the soil anaerobic bacteria convert nitrite ions back into N2. Exothermic process so provides energy in the abscence of aerobic pathways and completes Nitrogen cycle.

Front 79

What is the main anthropogenic nitrogen fixation. Give an example of a second.

Back 79

The Haber-Bosch process N2 + 3H2 --> 2NH3

leading synthetic chemistry process in the world.

Another source nitrogen oxides from burning fossil fuels

Front 80

What is a consequence of partial denitrification?

Back 80

N2O emissions, powerful greenhouse has, N2O causes ozone depletion

Front 81

Explain why 17 minutes after the Big Bang the mass distribution of elements in the universe was: 74% H+, 25% He2+ and 1% Li+

Back 81

In the last three minutes of the first five minutes of the nucleus 1H to 7Li began being created. The first steps are the creation of Hydrogen isotopes. E.g. 1H+ + n --> 2H+ +γ. One way these nuclei can fuse is called nuclear fusion;

3H+ + 2H+ --> 4H2+ + H+. Formation of an alpha particle. After 17 mins the universe was too cool for fusion to continue.

Front 82

As gas clouds come together through gravity they become dense and hot enough for fusion to occur again. What process does it do this by and what energy is released on fusion?

Back 82

Proton-proton chain, energy released on fusion is binding energy.

Front 83

Why is nuclear fusion alone not a good method to form higher elements?

Back 83

Because they will be highly unstable and instantly decay back into smaller nuclei.

E.g. 4He2+ + 4He2+ <--> 8Be2+ is endothermic

Front 84

What process allows the nuclear fusion of higher elements? Give an example with 8Be2+.
What can be noted about fusion of different elements?

Back 84

The triple alpha process. As hydrogen fuel runs out the core of the star begins to collapse resulting in an increased density and increased temperature. In these conditions SOME of the 4He2+ fusion occurs, 8Be2+ still decays back but a steady state concentration of Be is created.

4He can then undergo fusion with 8Be to forms a steady state of 12C. As 12C builds up it can fuse with 4He to create 16O etc. This is an exothermic process

Front 85

Why does He fusion to form other elements in triple alpha process and not H?

Back 85

Because although more energy is released from burning H, He is consumed much faster which is important due to short life-time of heavier nuclei.

Front 86

What occurs when stars 4 and 8 times the suns mass finish He burning respectively?

Back 86

4 times: 12C burning triggered, 12C + 12C --> 24Mg + energy

8 times: O and Ne burning triggered

Front 87

Why is less energy released for higher fusion processes? What is a result of this?

Back 87

The difference in binding energy decreases. As a result exothermic fusion processes end with Ni.

Front 88

What is the S-processes nuetron capture? where does it terminate? Why does this process not work for some nuclides?

Back 88

A process in which nuclei heavier than 56Ni are created. Slow neutron capture mainly occurs in red giant stars with neutrons mainly coming from 13C + a --> 16O + n and 22Ne + a --> 25Mg + n. Terminates at Bi. Many neutron rich molecules cannot be produced as neutron flux is low and unstable nuclei will b-decay in to more stable nuclides.

Front 89

What is the R-process and where does it exclusively occur?

Back 89

The R-process occurs exclusively in a supernova, and is responsible for half of nuclides with a mass higher than 56Fe, and all nuclides with a mass higher than 209Bi. The intense heat results in a higher neutron flux that cancels out the b-decay

Front 90

Why is there are a high population of Be and B?

Back 90

Due to spallation, the collision of nuclei at high energy providing lower mass fragments.