Transcript The_Carbon_Story 4276KB Aug 17 2012 12

The Carbon Story
The stuff of life
All you ever wanted to know but were afraid to ask.
Atoms and molecules
The simplest known substances are called
“elements”
an element has only one type of atom
There are 92 naturally occurring elements
all other substances are made up from
assemblages of elements
Protons, electrons,
neutrons
an element is defined by its atomic structure
all atoms of a given element have the same
number of protons and electrons
this number determines its chemistry
some atoms of an element may have a
different number of neutrons
they are chemically the same but of slightly
different mass
Isotopes of Carbon
all carbon atoms have six electrons and six protons
most carbon atoms also have 6 neutrons
some carbon atoms have 7 or 8 neutrons.
carbon 14 (6p + 8n) is radioactive and has a half life
of 5,730 years and decays into nitrogen
it is constantly being created as cosmic rays strike
nitrogen atoms in the atmosphere
the amount of carbon 14 in the atmosphere is
reasonably constant. (1 part per trillion)
Carbon dating
the carbon dioxide taken up by plants therefore
contains a known proportion of carbon 14
when the plant dies, the carbon 14 level slowly decays
as carbon 14 breaks down back into nitrogen
the amount of carbon 14 in a sample compared to its
carbon 12 is an indicator of its age.
carbon dating is useful for periods of time measured in
thousands of years
dating the carbon in charcoal from ancient fires tells us
that aboriginal people have lived in Australia for
something like 40,000 years
Allotropes
some elements present in more than one physical form
the two forms usually have the same chemistry
in the case of carbon the two forms are:
graphite (one of the softest substances known)
diamond (the hardest naturally occurring substance)
carbon atoms are able to bond to each other
they do this by sharing pairs of electrons
this gives carbon some interesting and unique
properties
for example, carbon atoms can combine into long
chains or into rings
Diamon
d
under the right circumstances of temperature and
pressure, carbon atoms can link up into a grid
each atom has 4 neighbours arranged at the points of a
tetrahedron
this is a very strong and rigid structure
but…
although diamond is very hard and can scratch steel
and glass
it is very fragile and will shatter if stuck
because it is pure carbon it will burn to form carbon
dioxide.
because there are no free electrons diamond is an
insulator.
Graphite
the carbon atoms are arranged into a planar
hexagonal grid
these layers of grids are not linked and can slide over
each other
graphite is very soft
each atom is linked to three other atoms
there are free electrons which can move - graphite is a
good conductor of electricity
graphite has many familiar forms
pencil “lead” is actually graphite mixed with clay
charcoal (partly burnt wood)
activated charcoal, formed by heating charcoal in
steam, is a useful filter substrate
lampblack formed as ‘soot’ when oils burns in a
limited air supply
boneblack derived from animal bones
coal
coke
Carbonates and
bicarbonates
the radicals CO3 & HCO3 are commonly
occurring and found in most homes
washing soda - Na2CO3
bi-carb soda - NaHCO3
limestone and marble CaCO3
carbonate and bi-carbonate radicals are formed when
carbon dioxide dissolves in water
CO2 + H2O ----> H2CO3 ----> 2H+ + CO32hydrogen ions are the basic part of acids
this makes the water mildly acidic
under pressure, more carbon dioxide will dissolve in
water
when the pressure is released the gas comes back ‘aerated’ or carbonated waters and sparkling wines,
‘soda siphon’
some carbonates are water soluble
some carbonates are not water soluble
the test for CO2 is to pass the gas into ‘lime water’
Ca(OH)2 + CO2 ----> CaCO3 + H2O
the calcium carbonate is insoluble and makes the water
go cloudy.
adding further CO2 clears the water again
CaCO3 + H2O + CO2 ----> Ca(HCO3)2
calcium bicarbonate is water soluble
all rain and ground water contains some dissolved
carbon dioxide
such water passing over limestone (CaCO3) will cause it
to dissolve
as the water evaporates the carbon dioxide is released
and the calcium carbonate re-forms
this is what creates stalactites and stalagmites in
limestone caves
carbon dioxide is produced when…
carbonates are heated
acid is added to carbonates or bi-carbonates
carbon is burned in air (or oxygen)
compounds containing carbon are burned in air (or
oxygen)
frozen carbon dioxide is called ‘dry ice’
its freezing temperature is about -80°C
under normal atmospheric pressure it converts from the
solid form directly into the gas without going through the
liquid phase
liquid carbon dioxide only exists under high pressure
because carbon dioxide is a product of combustion, it
cannot burn. It is used in fire extinguishers
carbon monoxide
when carbon or carbon containing substances burn in
insufficient oxygen the gas produced is carbon monoxide
carbon monoxide will quickly change to carbon dioxide if
exposed to air
it burns with a blue flame
in the human body, carbon monoxide easily combines
with haemoglobin in the same way as oxygen but cannot
be released
carbon monoxide has no odour
Organic Chemistry
The chemistry of organisms
the chemistry of carbon
the chemistry of life
hydro-carbons
carbon can form into chains of varying lengths
each carbon atom can bond to hydrogen
methane (odourless) found in marsh gas CH4
ethane C2H6
propane C3H8
butane C4H10, pentane C5H12, hexane C6H14, heptane
C7H16, octane C8H18, nonane C9H20, decane C10H22
Isomers have the same basic chemistry but different physical
properties.
Unsaturated chains
Triple bond unsaturated chains
Also known as acetylene
limestone (calcium carbonate CaCO3) heated to drive off the carbon dioxide to produce
quick lime (calcium oxide CaO)
calcium oxide heated with coal (carbon C) at about 2000°C in an electric arc furnace
(graphite electrodes)
CaO + 3 C -----> CaC2 + CO
CaC2 + 2 H2O -----> C2H2 + Ca(OH)2
Alcohols
also known as wood alcohol - poisonous, leading to blindness and death.
this is the alcohol in wines, beers, spirits etc. It is a mild anaesthetic and
depressant.
Denatured alcohol, also known as methylated spirits is ~90% ethanol and ~10% methanol
with a small amount of pyridine (nasty smell)
There is a whole series of alcohols, systematically named: propanol, butanol, pentanol etc.
Aromatics & other interesting compounds
6 carbon atoms can link up in a hexagonal ring. On close examination you can
see that each carbon has only three bonds. The ring indicates that there are 6
unbonded electrons which appear to exist distributed around the ring rather
than belonging to a particular atom.
Hydrogens can be replaced by other atoms or radicals. An OH (hydroxyl
group) makes an alcohol.
Here a methyl radical creates toluene.
Vanilla essence!
vanillin
trinitrotoluene
black = carbon
white = hydrogen
blue = nitrogen
red = oxygen
Let’s get rid of those silver fish!
Other stuff
The ether used as an anaesthetic is di-ethyl ether C2H5OC2H5
There is a series of aldehydes. This is the one used to preserve tissue specimens
Acetone
There is a whole series of keytones. Acetone is a solvent used in nail polish remover.
Citral
Citral is present in the oils of several plants, including lemon myrtle (90-98%), Litsea
citrata (90%), Litsea cubeba (70-85%), lemongrass (65-85%), lemon tea-tree (70-80%),
Ocimum gratissimum (66.5%), Lindera citriodora (about 65%), Calypranthes parriculata
(about 62%), petitgrain (36%), lemon verbena (30-35%), lemon ironbark (26%), lemon
balm (11%), lime (6-9%), lemon (2-5%), and orange.
Organic Acids
Organic acids are characterised by a COOH group attached to a chain.
Formic acid is the characteristic smell and bite of ants
When wines “go off” they become acidic - acetic acid
Acetic acid vinegar
Citric acid is found in lemons. Annual world production (2007) 1.6 M tonnes
Citric acid
alcohol + organic acid ----> ester + water
Fatty Acids
palmitic acid makes up about 24% of human fat - CH3(CH2)14COOH
it is a saturated fat - ie. all single bonds, maximum amount of hydrogen
oleic acid makes up about 47% of human fat - CH3(CH2)7CH=CH(CH2)7COOH
it is an unsaturated fat - ie. it has a double bond
a poly unsaturated fatty acid has multiple double bonds
Soap
Take a triglyceride fat or oil and boil it up in sodium hydroxide (lye) and water
CH2OOCR
|
CH2OOCR + 3 NaOH ----->
|
CH2OOCR
fat/oil
CH2OH
|
CHOH + 3 RCOO-Na+
|
CHOH
glycerol soap
glycerol, glycerine
Add salt (NaCl) and the soap comes out of the solution. This is why bath soap doesn’t work in salt water.
Soap has an organic end (left) and an inorganic, water soluble end.
Detergent
CH3(CH2)17OSO3-Na+
Polymers
vinyl chloride
poly vinyl chloride pvc
neoprene
poly ethylene
polythene
Carbohydrates
sugars, starches, cellulose
The sugar we buy in the supermarket is called sucrose. It is called a disaccharide because it is actually formed from two
other simple sugars. It has the nominal formula C6H12O6. Note the ratio of hydrogen to oxygen (H2O)
Glucose
C6H12O6
H
|
C=O
|
HO-C-H
|
H-C-OH
|
HO-C-H
|
HO-C-H
|
H-C-OH
|
H
Fructose
C6H12O6
H
|
HO-C-H
|
HO-C=O
|
H-C-OH
|
HO-C-H
|
HO-C-H
|
H-C-OH
|
H
Starches have many more carbons in their structure.
There are alternate models including ring structures
Starches can be broken down into simple sugars
Some animals can break down cellulose into starches and sugars
The Carbon Cycle
Why growing trees is not the answer!
Photosynthesis
moss cells under the microscope
In the presence of light, the green structures inside plant cells called chloroplasts are the sites where carbon dioxide and water
are converted into carbohydrates. Oxygen is released as a waste product.
CO2 + H2O --light-> carbohydrate + O2
The green chemical is called chlorophyll.
Oxygen is very reactive. Metals quickly corrode in air because of the presence of oxygen.
So reactive is it, that it cannot exist in the atomic state so it is found in molecules as atom pairs - O2
A second form of oxygen known as ozone consists of three atoms of oxygen linked together - O3. It is poisonous and has the
characteristic smell associated with sparks. It has a half life of about 30 minutes. It breaks down into O2.
It forms in the upper atmosphere where ultraviolet light interacts with O2 to form O3.
Oxygen makes up about 20.8% of the air
All the oxygen in the atmosphere has been produced by green plants over the last 2.5 billion years.
Carbon dioxide makes up about 0.039% of air by volume
Respiration
Cellular respiration is the process of combining nutrients, predominantly carbohydrates, with oxygen to release energy to
power the chemistry of the cells functions.
This process applies to both plants and animals.
The waste product is CO2.
In the case of an animal, the air breathed out contains less oxygen and more carbon dioxide than the air which is
breathed in.
Expired air still contains oxygen - that’s why the “kiss of life” works.
The raised CO2 content in the lungs triggers the breathing reflex.
The carbon system is dynamic
carbon is constantly migrating through various forms
carbon is entering and leaving the atmosphere all the time.
in the biosphere, carbon is the vector which carries energy
collected from the sun into biological processes.
As the energy is released the carbon returns to the atmosphere
to “go ‘round again”
but…
Not all carbon is created equal.
The key is to be found in the length of the cycle
Not all carbon dioxide is “created” equal.
What is important is the time scale
associated with its production and removal
from the atmosphere.
Grass grows during the spring and summer
and is eaten by various animals - cattle,
sheep, ‘roos, …
The life of a tree is of the order of 100
years. In that time a forest will come into a
state of equilibrium. After that time the
amount of carbon in the forest is largely
constant.
When a tree dies it is consumed by various
other plants and animals. The forest
ecosystem has the available nutrients
constantly being recycled.
Break down of carboniferous material
releases carbon dioxide into the
atmosphere at the same rate that
photosynthesis removes it.
A - grasses
B - trees
C - long lived trees
D - oil
E - coal
The longest lived trees have life
expectancy at around 1000 years.
Oil deposits were laid down 70+ million
years ago. Some as much as 400 Ma
Carbon removed from the air by small
marine organisms around 100 Ma has
remained stored away from the air in
geological basins.
Coal deposits age from around 300 Ma.
Land plant material has been converted
into coal after burial and has remained
stored underground.
A - grasses
B - trees
C - long lived trees
D - oil
E - coal
The Carboniferous is a geologic period and system that extends from the end of the
Devonian Period, about 359.2 ± 2.5 Ma (million years ago), to the beginning of the Permian
Period, about 299.0 ± 0.8 Ma
Terrestrial life was well established by the Carboniferous period. Amphibians were the
dominant land vertebrates, of which one branch would eventually evolve into reptiles, the
first fully terrestrial vertebrates. Arthropods were also very common and many were much
larger than those of today. Vast swathes of forest covered the land, which would eventually
be laid down and become the coal beds characteristic of the Carboniferous system
Atmospheric carbon dioxide was much higher than it is today. Prolific plant life was
removing carbon dioxide from the air to build tissue.
As these forests died and were buried, what we now see as coal seams were formed.
These seams represent carbon which has been removed from the atmosphere and
sequestered underground for hundreds of millions of years.
The greenhouse effect
Light enters by passing through the glass and falls on the soil and plants inside.
This raises the temperature at ground level.
The air near the ground is warmed and rises to circulate inside the enclosure.
The Eden Project in Cornwall,
England, the world’s largest
greenhouse
Some heat is radiated back as infra-red radiation to which the glass is only partially
transparent. Some of this radiation is reflected back.
Atmospheric material acts in the same way.
Water vapour, CO2 and CH4 are only partially transparent to infra-red light.
This can be a temporary effect. In winter, a cloudless night presages a frosty morning. The ground temperature goes below
zero as heat energy is radiated out into space. The air near the ground is cooled close to or below zero. See the difference
a cloudy night makes to the temperature at the surface.
Greenhouse gas
A greenhouse gas (GHG) is a gas in an atmosphere
that absorbs and emits radiation within the thermal
infrared range. This process is the fundamental cause of
the greenhouse effect.
The primary greenhouse gases in the Earth's
atmosphere are water vapour, carbon dioxide, methane,
nitrous oxide, and ozone.
In the Solar System, the atmospheres of Venus, Mars,
and Titan also contain gases that cause greenhouse
effects.
Greenhouse gases greatly affect the temperature of the
Earth; without them, Earth's surface would be on
average about 33 °C colder than at present.
Since the beginning of the Industrial Revolution the
burning of fossil fuels has contributed to the increase in
carbon dioxide in the atmosphere from 280 ppm to
397 ppm, despite the uptake of a large portion of the
emissions through various natural "sinks" involved in the
carbon cycle.
Anthropogenic CO2 emissions (i.e., emissions produced
by human activities) come from combustion of
carbonaceous fuels, principally wood, coal, oil, and
natural gas.
Removing CO2 from the atmosphere
Photosynthesis converts CO2 to carbohydrates - the CO2 is stored for periods of 1 to 1000 years
CO2 is soluble in water
Some of this CO2 is removed from the water by shell building animals as CaCO3
As more CO2 is added, the water becomes acidic
insoluble CaCO3 may become water soluble Ca(HCO3)2
The ability of shelled organisms made from CaCO3 to acquire needed calcium is reduced or may stop
Keeping CO2 out of the atmosphere
Sequestration
To be effective, the carbon has to stay out of the atmosphere as part of the normal cycles.
Burning oil and coal releases carbon which has been stored for millions of years. To complete the cycle it needs to be
removed and stored for equivalent millions of years.
Can we capture and store the CO2 in some way?
Pump it into deep ground water under pressure?
Plough it into the soil?
Climate Change
On average, the earth’s surface temperature is rising
Since the early 1900’s this has amounted to about 0.8°C
2/3 of that rise has happened since 1980
What effects can be measured?
Sea surface temperatures are rising
Hot liquids expand
The amount of water in the atmosphere is rising
Sea level will increase by thermal expansion
The amount of energy in the atmosphere is increased
This energy drives the weather
We can expect more extreme weather effects
Ice which is now stored on land (Antarctica, Greenland,
glaciers) will melt adding more water to the oceans
Sea level will rise
Are there other factors which cause climate change?
Anything which effects the relationship between arriving energy from the sun and radiation of energy back into space
and
anything which effects the movement of energy around the earth
Sun activity levels
Continental drift
Ocean currents
Positive feedback
Jet streams
Precession of the poles
Magnetic field reversals
Large seismic events
Volcanic eruptions
Meteors and meteorites
Variations in the earth’s orbit
The 10 indicators are:
Land surface air temperature as measured by weather stations. You know all those skeptic arguments about how the
temperature record is biased by the urban heat island effect, badly-sited weather stations, dropped stations, and so on?
This is the only indicator which suffers from all those problems. So if you’re arguing with somebody who tries to frame the
discussion as being about land surface air temperature, just remind them about the other nine indicators.
Sea surface temperature. As with land temperatures, the longest record goes back to 1850 and the last decade is warmest.
Air temperature over the oceans.
Lower troposphere temperature as measured by satellites for around 50 years. By any of these measures, the 2000s was
the warmest decade and each of the last three decades has been much warmer than the previous one.
Ocean heat content, for which records go back over half a century. More than 90% of the extra heat from global warming is
going into the oceans – contributing to a rise in…
Sea level. Tide gauge records go back to 1870, and sea level has risen at an accelerating rate.
Specific humidity, which has risen in tandem with temperatures.
Glaciers. 2009 was the 19th consecutive year in which there was a net loss of ice from glaciers worldwide.
Northern Hemisphere snow cover, which has also decreased in recent decades.
Perhaps the most dramatic change of all has been in Arctic sea ice. Satellite measurements are available back to 1979 and
Global warming is better described as
Climate Change
Weather
Seasons
This is the day to day variation in atmospheric
conditions.
We a measure:
temperature
air pressure
This is the annual changes in weather patterns caused by
the fact that the earth’s axis is inclined to the plane of the
orbit around the sun.
The sun apparently changes its vertical position in the sky
and therefore the angle at which the suns rays strike the
earth’s surface at any given place changes during the year.
wind speed and direction
precipitation - rain, snow etc.
cloud amount
sun light
Climate
The long term average of the day to day variations of all the
measured quantities
This average can be struck for every day of the year - the
daily average
It can be struck for the whole month
It can be taken over the whole year.
Climate is also variable
accumulated sediments in lakes can show how run-off varies over a long term
the width of some tree rings responds to rainfall and others to temperature
ice cores taken in Antarctica hold an annualised record of snow accumulation and give an indication of climate
observing geological structures gives an indication of climate - eg. ice ages
Is the climate changing?
Definitely yes
Should we expect the climate to change?
Definitely yes
Is man contributing to climate change?
Definitely yes
Can we do anything about it?
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