Coral Reef Dissolution

Coral reefs dominate much of the world's tropical coastline, covering about 15% of the seabed shallower than 30 metres.

The largest coral reef in the world is the Great Barrier Reef off the north-east coast of Australia.

What impact will increasing amounts of atmospheric carbon dioxide have on our coral reefs?

Find out in this edition of AUS-e-NEWS!

If you haven't received your copy of AUS-e-NEWS, or if you would like to subscribe to our free quarterly newsletter, AUS-e-NEWS, the email us at

 

Bioethanol Fireplaces

Ethanol burners are becoming very popular in homes in Australia, often sold as "bioethanol" fireplaces. Although how "bio" your ethanol is really depends on which brand of ethanol or methylated spirits you choose to buy.
Having got some advertising mileage out of sticking the prefix "bio" onto ethanol, the glossy advertising brochure then adds some more enticing words like "eco", "friendly", "green" and/or "smart".
But the real selling point of the slick advertising is that you don't need a flue. No chimney, no pipes, just set your "bioethanol" fireplace up where ever you want it in the room.
Which is really very, very, interesting (for all you Chemists out there).

Chemistry of Combustion
Ethanol combusts (burns) by combining with oxygen gas in the atmosphere.
A balanced chemical equation for the complete combustion of ethanol is:

C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O

This tells us that for every 1 mole of ethanol (whether it has the "bio" prefix or not), 2 moles of carbon dioxide gas will be evolved (and yes, that's the same carbon dioxide gas that contributes to the greenhouse effect).

According to the brochure, 5 litres of "bioethanol" would last about 10 hours.
That is, 1 litre of bioethanol keeps your fire going for about 2 hours, just enough to watch a movie.
So how much carbon dioxide will be released into your room while you watch the movie?

First we can use the density of ethanol and the volume of ethanol burnt to calculate the mass of ethanol consumed:

• Density of ethanol is 0.79 g cm³ at 25^oC

• If we let 1cm³ = 1 mL

• then the mass of 1 mL of ethanol is 0.79 g

• so the mass of 1 L of ethanol = 1000 x 0.79 g = 790 g

Now we can calculate the moles of ethanol in the 1 L of "bioethanol" we burnt:

• moles = mass/molar mass

• molar mass = 2 x 12 + 6 x 1 + 16 = 46 g/mol

• so moles of ethanol in 1 L = 790/46 = 17.2 mol

Use the balanced chemical equation to calculate the moles of carbon dioxide produced:

• From the balanced chemical equation, 1 mole of ethanol burns to produce 2 moles of carbon dioxide gas.

• Therefore, 17.2 moles of ethanol burns to produce 2 x 17.2 moles of carbon dioxide gas.

• moles of carbon dioxide produced = 34.4 moles

We can then calculate the volume of carbon dioxide released into your room while you watch the movie:

• At 25^oC, 1 mole of gas occupies a volume of 24.79 L

• So, 34.4 moles of carbon dioxide occupies a volume of 34.3 x 24.79 = 853 L

853 L of carbon dioxide gas sounds like lot!
But is it really? What proportion of the "air" in your room will be carbon dioxide after 2 hours?

Let's calculate the volume of a room:

• A small room is about 3m x 3m x 3m

• or 300cm x 300cm x 300cm = 27,000,000 cm³ = 27,000 L

• So the volume of air in the room before you start burning your ethanol is 27,000 L(ignoring loss of volume due to you and the furniture )

And now we can see what proportion of the "air" in your room will be carbon dioxide after 2 hours:

• Assuming there is no ventilation in the room (all the doors and windows are closed), burning 1 L of ethanol adds about 853 L carbon dioxide gas to the room, so the total volume of gas is now 27,853 L.

• The percentage of that due to the carbon dioxide we have produced is 853/27853 x 100 = 3%

Now that's better, 3% sounds a whole better than 853 L doesn't it?
Or does it?

Did you know that at a concentration of about 1%, carbon dioxide will make you feel sleepy.
At a concentration of about 7%, you can suffocate.
Which makes you think you should probably be opening a window!
Except, wouldn't that defeat the purpose of lighting a fire to keep warm in the first place?

Suggested Study Questions:

1. Draw a structural formula for ethanol.
2. Explain the difference between complete and incomplete combustion of ethanol.
3. How you could you tell by observation whether the ethanol in your "bioethanol" fireplace was undergoing complete combustion or incomplete combustion?
4. The glossy brochure states that your "bioethanol" fireplace will not produce soot. What does this tell you about the type of combustion occurring in the fireplace?
5. If the ethanol in the "bioethanol" fireplace was undergoing incomplete combustion, would the amount of carbon dioxide produced be more or less than that produced during complete combustion?
6. Calculate the moles of carbon dioxide gas that would be produced if you burnt 1 L of "bioethanol" fuel in your fireplace in a room that measured 5m x 7m x 3m
7. What volume of the room in question 6?
8. At 25^oC, how many moles of gas are present in this room from question 6?
9. What percentage of gas in this room from question 6 would be carbon dioxide after you burn 1 L of "bioethanol"?
10. One of your friends suggests that you should take a "bioethanol" fireplace with you on your camping trip because it will be a perfect way to heat your tent. Do you agree with your friend or not? Explain your answer.

Amine Scrubbing

Fossil fuel-burning power plants, in particular coal-burning power plants, are a major source of a carbon dioxide, a greenhouse gas. When power plants begin capturing their carbon emissions to reduce greenhouse gases it will be an expensive undertaking. Current technologies use about one-third of the energy generated by power plants to capture greenhouse gas emissions, this is referred to as parasitic energy.

Although no commercial power plants currently capture carbon dioxide on a large scale, a few small-scale and pilot plants do. One commonly used process is known as amine scrubbing in which gas emissions are funneled through an amine bath, which absorbs carbon dioxide from the flue gases. Typical amine baths in use are:

• 32 % by mass aqueous 2-aminoethanol (NH₂-CH₂-CH₂OH) solution
• 25% by mas aqueous 2,2'-Iminodiethanol (HN(CH₂CH₂OH)₂) solution
• 40% by mass bis(2-hydroxyethyl)methylamine (CH₃N (C₂H₄OH)₂₎ solution
• 50% by mass 2-(2-Aminoethoxy)ethanol solution
  

 The amines are then boiled to release the CO₂. Additional energy is required to compress the carbon dioxide so that it can be pumped underground.
The energy needed for this process decreases the amount that can go into making electricity. Calculations show that for a coal-fired power plant, that could amount to approximately 30% of total energy generated.

A group of  scientists from UC Berkeley and EPRI have developed a computer model to calculate energy energy costs of carbon dioxide capture, release and compression, for any material including the amine baths above as well as zeolites (porous materials made of silicon dioxide) and MOFs (metal oxide frameworks).

Reference
Li-Chiang Lin, Adam H. Berger, Richard L. Martin, Jihan Kim, Joseph A. Swisher, Kuldeep Jariwala, Chris H. Rycroft, Abhoyjit S. Bhown, Michael W. Deem, Maciej Haranczyk, Berend Smit. In silico screening of carbon-capture materials. Nature Materials, 2012; DOI: 10.1038/nmat3336

Further Reading:
Greenhouse Gases and the Greenhouse Effect
Combustion of Hydrocarbons
Amines

Percent By Mass (weight) Concentration 
Zeolites


Suggested Study Questions:

1.  Give the name and formula of the four main naturally occurring greenhouse gases.
2. Give the name and formula of four human-induced greenhouse gases.
3. Write a chemical equation for the complete combustion of coal.
4. Anthracite is a type of coal that is made up of about 95% carbon. The combustion of 1g of coal releases about 1000 kJ of energy. Calculate the heat of combustion of anthracite in kJ/mol
5. Write the molecular formula for each of the 4 amines used in amine scrubbing baths.
6. On the structural formula for each of the amines used in amine scrubbers:
   • circle amino groups in blue
   • circle hydroxyl groups in red
7. For a 32% by mass aqueous 2-aminoethanol solution, calculate the mass of  2-aminoethanol present in
   • 1 kg of solution
   • 100 g of solution
   • 1 tonne of solution
   • 2500 mg of solution
8. What is the concentration in mol/L of the1 kg of  a 32% by mass aqueous 2-aminoethanol solution?

 

Ocean pH

Coccoliths are very small shells of calcium carbonate that form around a number of species of algae. Algae play an important role in the global carbon-oxygen cycle and thus in our ecosystem. Scientists at the Nano-Science Center, University of Copenhagen, have measured how individual coccoliths react to water with different degrees of acidity.

Coccoliths which have a mass of about 500 pg (0.0000000005 g), were weighed before and after they had been immersed in water with different acidities. The results enable the scientists to say something about how important the water acidity is for the marine environment.

The world's oceans are acidifying due to our emissions of carbon dioxide. Over time the pH of the Earth's oceans is decreasing:

Time	pH
18th century	8.179
Recent past (1990s)	8.104
Present levels	~8.069
2050 (estimated)	7.949
2100 (estimated)	7.824

Coccoliths are protected from dissolution by a very thin layer of organic material that the algae form, even though the seawater is extremely unsaturated relative to calcite (calcium carbonate). The protection of the organic material is lost when the pH is lowered slightly. In fact, it turns out that the shell falls completely apart when experiments are done in water with a pH value of 7.8, the pH that many researchers believe will be the found in the world oceans in the year 2100.

Reference:
T. Hassenkam, A. Johnsson, K. Bechgaard, S. L. S. Stipp. Tracking single coccolith dissolution with picogram resolution and implications for CO2 sequestration and ocean acidification. Proceedings of the National Academy of Sciences, 2011; DOI: 10.1073/pnas.1009447108\

Further Reading:
Carbon Cycle
Combustion of Hydrocarbons
Acid Rain
Mass Conversions
pH Calculations
Acid Dissociation Constants (Ka)

Study Questions:

1. Write the formula for:
   
   • carbon dioxide
   • calcium carbonate
2. Calculate the percentage composition of
   
   • carbon dioxide
   • calcium carbonate
3. Write a balanced chemical equation to show the production of carbon dioxide from the combustion of methane (a fossil fuel).
4. Assuming 100 tonnes of methane gas were combusted under standard laboratory conditions:
   
   • What is the maximum mass of carbon dioxide that could be produced?
   • What volume would this mass of carbon dioxide occupy?
5. Coccoliths have a mass of about 500 pg. Convert this to a mass in:
   • milligrams
   • micrograms
   • nanograms
   • kilograms
6. The current pH of ocean water is approximately 8.069. Assuming the temperature of the oceans to be 25^oC, calculate the current:
   • hydrogen ion concentration of ocean water
   • hydroxide ion concentration of ocean water
   • pOH of ocean water
   
   
7. In 2100, the pH of ocean water is predicted to be 7.824. Assuming the temperature of the oceans to be 25^oC, calculate the:
   • hydrogen ion concentration of ocean water in 2100
   • the hydroxide ion concentration of ocean water in 2100
   • the pOH of ocean water in 2100
   • the increase in hydrogen ion concentration between now and 2100
     
   
   
   
8. For the reaction: H₂CO₃ HCO₃^- + H⁺ K_a = 4.5 x 10^-7
   
   • Is H₂CO₃ a strong acid or weak acid? Explain your answer.
     
   • Calculate the concentration of H⁺
   • Calculate the pH of the solution.
   • Calculate the pOH of this solution at 25^oC.
   • Calculate the concentration of hydroxide ions at 25^oC.
   • Explain what impact an increase in hydrogen ion concentration would have on this equation.
     

Making Methanol

Methanol as an energy source can be used as a fuel in the same way as petrol (gasoline), or it can be used in fuel cells. About 90% of the worldwide production of methanol is derived from methane, the main component of natural gas. Current methods for producing this methanol involve converting methane into syngas, a mixture of carbon monoxide and hydrogen, and then converting this syngas into methanol. Eliminating the syngas stage would dramatically reduce the cost of producing methanol.
But methane is not very reactive, and combines readily with oxygen only at high temperatures. A catalyst helps, but commonly used catalysts themselves work only at 300^oC or higher. At these temperatures, most of the methanol produced is oxidized to carbon dioxide and water. Indeed, methanol yields from such reactions can be as low as 2%.

A lower temperature catalyst such as platinum dissolved in concentrated sulfuric acid at 200^oC, has achieved a methanol yield of more than 70% in the laboratory, but platinum is an expensive metal.

Methane can also be converted to methanol in the laboratory using a halogen such as bromine. Using a suitable catalyst at 250^oC methane reacts with bromine to form bromomethane (methylbromide) and hydrogen bromide. Bromomethane (methyl bromide) then reacts with water to form methanol. The bromine from the hydrogen bromide can be recovered by reaction with air, and reused.

Methanol can be made by combining carbon dioxide and hydrogen. Such a process requires considerable energy just to harvest the hydrogen from water, for example. The carbon dioxide could be captured from flue gases, and even directly from the atmosphere.

Further Reading
Nomenclature
Alcohols
Balancing Chemical Equations
Combustion of Hydrocarbons
Halogenation of Hydrocarbons
Fuel Cells and Batteries
Temperature Conversions
Ideal Gas law
Yield

Study Questions

1. Write the chemical formula for each of the following:
   
   • methanol
   • methane
   • carbon monoxide
   • hydrogen gas
   • oxygen gas
   • carbon dioxide
   • water
   • bromine liquid
   • bromomethane (methylbromide)
   • hydrogen bromide
2. Write balanced chemical equations for each of these reactions:
   
   • carbon monoxide + hydrogen gas → methanol
   • carbon dioxide + hydrogen gas → methanol
     
   • methane + oxygen gas → carbon dioxide gas + water
   • methane + oxygen gas → methanol
   • methane + bromine liquid → bromomethane + hydrogen bromide
   • bromomethane + water → methanol + hydrogen bromide
     
   • water → hydrogen gas + oxygen gas
3. Convert the following temperatures in ^oC to Kelvin
   • 200^oC
   • 250^oC
   • 300^oC
   
   
4. For the reaction between methane and oxygen to produce methanol, calculate the theoretical yield of methanol that could be produced from 100kg of methane.
5. Using the platinum-based sulfuric acid catalyst at 200^oC, yields of 70% have been achieved for the above reaction.
   • What mass of methanol is actually produced during this reaction if you start with 100kg of methane?
   • Convert this mass to moles.
   • Calculate the volume of methanol gas produced.
     
6. At 300^oC the yield of methanol produced from the reaction between methane and oxygen is 2%. Assume the reaction starts with 100L of methane gas
   • Calculate the moles of methane gas in the reaction mixture
   • Calculate the theoretical yield of methanol that could be produced
   • Calculate the actual yield of methanol
7. Why do you think it is important for Chemists to continue to search for inexpensive catalysts for the methane to methanol reaction?
   
   

Carbon Capture and Storage (CCS)

Combustion of fossil fuels, such as coal, fuel oil, or natural gas, liberates large quantities of carbon dioxide, a gas that significantly affects global climate. A key technology that would reduce emissions and lead to more environmentally friendly power plants is the capture and storage of carbon dioxide from flue gases of power plants (carbon capture and storage (CCS)). CCS might be able to reduce CO₂ emissions resulting from the employment of fossil fuels for power generation and other uses in industry to near zero and thereby contribute to reducing greenhouse-gas emissions.
The Technische Universität Darmstadt has dedicated a pilot plant for capturing carbon dioxide contained in flue gases of power plants using two new methods:

• carbonate looping
• chemical looping

Carbonate looping involves utilizing naturally occurring limestone to initially bind CO₂ from the stream of flue gases transiting power plants' stacks in a first-stage reactor. The resultant pure CO₂ is re-liberated in a second reactor and can then be stored. The advantage of the carbonate-looping method is that even existing power plants can be retrofitted with this new method.

Chemical looping allows CO₂ to be captured with hardly any loss of energy efficiency. Under this method, a dual-stage, flameless, combustion yields a stream of exhaust gases containing only CO₂ and water vapor. The CO₂ can then be captured and stored.

Reference
Technische Universität Darmstadt (2010, November 7). On the way to CO₂-free power plants. ScienceDaily. Retrieved November 8, 2010, from http://www.sciencedaily.com­ /releases/2010/11/101103082306.htm

Further Reading
http://www.ausetute.com.au/combusta.html
http://www.ausetute.com.au/idealgas.html
http://www.ausetute.com.au/heatcomb.html
http://www.ausetute.com.au/greenhouse.html
http://www.ausetute.com.au/ccycle.html

Study Questions

1. Explain what is meant by the term fossil fuel.
2. Write a balanced chemical equation to represent the complete combustion of coal.
3. Write a balanced chemical equation to represent the complete combustion of natural gas.
4. If you burnt 1kg of coal and 1kg of natural gas, which reaction would produce the greatest amount of carbon dioxide?
5. If you burnt 1000cm³ of solid coal, and 1000cm³ of gaseous methane, which reaction would produce the greatest amount of gaseous carbon dioxide?
6. The heat of combustion of methane is 890 kJ/mol. Is energy released or absorbed during this reaction?
7. When coal burns it releases energy, about 250 kJ/mol. At 25^oC and 1 atmosphere pressure, is methane or coal the better fuel?
8. What benefits are there in storing the carbon dioxide emitted during power generation?
9. What disadvantages are there in storing carbon dioxide emitted during power generation?
10. What impact could the storage of this carbon dioxide have on the natural carbon cycle?
    

A New Look at Evaporation

As much as 71% of Earth is covered by oceans and seas which evaporate continuously. Since the heat of evaporation of water is very high, the evaporation determines Earth's climate. What is more, the content of water vapour, the main greenhouse gas, in the atmosphere changes as a result of evaporation. Its concentration in air may reach as much as 4%, more than hundred times higher than that of the infamous carbon dioxide. According to various estimates, if there was no water vapour in air, the temperature on Earth would fall by 20-30 degrees.
The first scientific publication concerning the mechanism of evaporation was written by the famous physicist James Clerk Maxwell, but Polish scientists investigating evaporation are questioning how well we understand the phenomenon.
The investigation studied a drop of liquid in a closed vessel in equilibrium with its vapour. During evaporation the most interesting events take place on the border of a liquid and a vapour. The thickness of this interface is more or less equal to the diameter of an atom.
"Maxwell assumed that evaporation took place at constant temperature. It is so, if we look at the initial state, that is a liquid, and the final state, that is a vapour. It is true that their temperatures are equal. But during the evaporation process itself, the nature acts in a completely different way," explains Ph.D. Marek Litniewski from IPC PAS.
The existing description assumed that the heat transfer in the system was stable and the rate of evaporation was limited by the efficiency of the process during which the particles break away from the surface of drops, i.e. diffusion. However, the simulation carried out in the IPC PAS showed that during the evaporation into vacuum or the liquid's own vapour the system gained mechanical equilibrium very quickly. Particles break away from the surface of a liquid and their mechanical recoil allows the equalisation of the pressure inside the drop. If the rate of evaporation on the surface achieved the maximum value and the system was still unable to equalise the pressures, spaces with new surfaces would open inside the drop and it would start to boil. However, it was observed that the mechanical equilibration of pressure can be insufficient and the temperature on the surface of the liquid decreases: the drop aims at maintaining the pressure equilibrium at the cost of its internal energy. This observation suggests that the factor that is crucial during evaporation is not the diffusion of particles into the environment but the heat transfer and the equality of pressures.

Reference:
Institute of Physical Chemistry of the Polish Academy of Sciences (2010, October 20). Everything evaporates, but how?. ScienceDaily. Retrieved October 21, 2010, from http://www.sciencedaily.com­ /releases/2010/10/101020084149.htm

Further Reading
http://www.ausetute.com.au/chemphys.html
http://www.ausetute.com.au/intermof.html
http://www.ausetute.com.au/equilibrium.html
http://www.ausetute.com.au/heatlatent.html
http://www.ausetute.com.au/greenhouse.html

Study Questions

1. Write a chemical equation to describe the evaporation of water.
2. Is the evaporation of water a chemical or a physical change? Explain your answer.
3. Give the names and formulae of 4 natural greenhouse gases.
4. Give the names and formulae of 4 human-induced greenhouse gases.
5. Briefly explain what is meant by the terms Greenhouse Effect and Enhanced Greenhouse Effect.
6. What would be the difference between studying the evaporation of a water droplet in a closed vessel compared to studying the evaporation of a water droplet in a vessel open to the air?
7. Imagine you were undertaking a study of the evaporation of a water droplet in a closed system. In the first experiment you maintain a constant temperature of 25^oC and in the second experiment you maintain a constant temperature of 65^oC. What differences would you expect in the results of your study?
   

Dry Water

Discovered in 1968, "dry water" consists of 95% water, yet it is a dry powder which resembles powdered sugar at room temperature and pressure. Each powder particle contains a water droplet surrounded by modified silica. The silica coating prevents the water droplets from combining and turning back into liquid water. The result is a fine powder that can slurp up gases which combine with the water molecules to form hydrates.

Dry water can absorb over three times as much carbon dioxide gas as ordinary uncombined water and silica in the same length of time. This ability to absorb large amounts of carbon dioxide gas as a hydrate could make it useful in helping to reduce global warming since carbon dioxide gas is a major contributor to global warming.

Dry water can also be used to store methane, a component of natural gas. This could provide a safer, more convenient way to store methane fuel for use in vehicles powered by natural gas.

Reference:
American Chemical Society (2010, August 25). 'Dry water' could make a big splash commercially. ScienceDaily. Retrieved August 26, 2010, from http://www.sciencedaily.com­ /releases/2010/08/100825174102.htm

Study Questions

1. Write the chemical formula for each of the following compounds:


• water


• silica


• carbon dioxide


• methane




2. Draw a diagram to represent the molecular structure of dry water powder.
3. Draw a diagram to represent the structure of hydrated carbon dioxide.
4. Explain how water can absorb carbon dioxide.
5. Explain how silica can absorb carbon dioxide.
6. Explain why dry water is so much better at absorbing carbon dioxide than either pure water or silica.
7. Write a chemical equation to represent the production of hydrated methane.
8. Using the equation above, discuss how dry water could be used to store and release methane for use in vehicles powered by natural gas.