Dioxins in Sydney Harbour

Data collected by the NSW Department of Environment, Climate Change and Water (Australia) in 2008 shows that large tracts of sediments in Sydney Harbour are more contaminated with dioxins than Tokyo Bay or New York Harbour, and are among the most contaminated in the world.
In the remediation area in Homebush Bay, the location of the 2000 Sydney Olympic Games, the dioxin levels were 610 picograms per gram of sediment compared with 2.3 for a "clean" environment. These high levels of dioxins in areas where fish feed means the warning not to eat fish caught west of the Sydney Harbour Bridge, and to eat only 150 grams a month of fish caught east of the bridge, will most likely have to remain in place for decades.

The source of the contamination is the former Union Carbide site where dioxins were used in the manufacture of the now-banned pesticide 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) and the defoliant Agent Orange which was used during the Vietnam War.

Dibenzo-p-dioxin is made up of two benzene rings joined by two oxygen bridges, so it is an aromatic diether.
The name dioxin actually refers to the central dioxygenated ring. So, if other elements are substituted for the hydrogen atoms in the molecule, they too would be referred to as dioxins. This means there are many different compounds that can be referred to as dioxins!

In common use, the term dioxins usually refers to polychlorinated dibenzodioxins (PCCDs) which are a group of chlorinated dibenzo-p-dioxin molecules. In PCCDs the chlorine atoms can attach on 8 different places on the dibenzo-p-dioxin molecule (shown as 1,2,3,4 and 6,7,8,9 on the structure above). The toxicity of PCDDs depends on the number and positions of the chlorine atoms. The most toxic dioxin is 2,3,7,8-tetrachlorodibenzo-p-dioxin, and is well known as the contaminant of Agent Orange.


Dioxins are known to build up in the human body over time, mostly in fatty tissues.
Exposure to high levels of dioxins causes a severe form of persistent acne known as chloracne and leads to an increased risk of tumours.
Exposure to low levels of dioxins results in an elevated risk of sarcoma, a type of skin cancer.

Reference:
http://www.smh.com.au/environment/water-issues/the-poison-that-got-away-20101029-177i0.html?autostart=1

Further reading
http://www.ausetute.com.au/massconv.html
http://www.ausetute.com.au/partspm.html
http://www.ausetute.com.au/namctut1.html
http://www.ausetute.com.au/namhaloa.html
http://www.ausetute.com.au/mmcalcul.html
http://www.ausetute.com.au/percentc.html
http://www.ausetute.com.au/namisane.html

Study Questions

1. Convert 610 picograms per gram to
• micrograms per gram
• nanograms per gram
• micrograms per milligram
• milligrams per kilogram
• parts per million
• parts per billion
2. Write the molecular formula for each of the following:
   • dibenzo-p-dioxin
   • 2,3,7,8-tetrachlorodibenzo-p-dioxin
3. Calculate the percentage composition of dibenzo-p-dioxin.
4. Calculate the mass of chlorine present in 610 picograms of 2,3,7,8-tetrachlorodibenzo-p-dioxin.
5. Indicate the location of ether functional groups on a molecule of dibenzo-p-dioxin.
6. Give the structural formula of as many different structural isomers of 2,3,7,8-tetrachlorodibenzo-p-dioxin as possible.
7. Name each of the molecules you have drawn in question 6.
   

Fracking

Marcellus shale is a massive rock formation that is possibly the largest source of natural gas in the USA. It extends from New York through Pennsylvania, Ohio and West Virginia. Marcellus shale naturally traps metals such as uranium at levels higher than usually found naturally but lower than man-made contamination levels.
Hydraulic fracturing, or fracking, is a process that results in the creation of fractures in rocks in order to tap into oil and natural gas deposits such as those present in Marcellus shale. Millions of gallons of water and chemicals are pumped deep underground to blast through the rocks in order to release the natural gas. University of Buffalo scientists have shown that the metals and the hydrocarbons are chemically bonded, so, the process of drilling to extract the hydrocarbons could force the metals into the soluble phase, enabling them to move around. When the millions of gallons of water used in hydraulic fracturing, or fracking, come back to the surface, it is likely to contain toxic uranium contaminants, potentially polluting streams and other ecosystems and generating hazardous waste.

Reference:
University at Buffalo (2010, October 27). Uranium in groundwater? 'Fracking' mobilizes uranium in marcellus shale. ScienceDaily. Retrieved October 29, 2010, from http://www.sciencedaily.com­ /releases/2010/10/101025172926.htm

Further Reading:
http://www.ausetute.com.au/usehydrc.html
http://www.ausetute.com.au/combusta.html
http://www.ausetute.com.au/chemphys.html
http://www.ausetute.com.au/fuelsdef.html

Study Questions:

1. What is the name and chemical formula of the major constituent of natural gas?
2. What is meant by the term hydrocarbon?
3. Give the names, chemical formulae, and uses for 3 other hydrocarbons.
4. Explain what is meant by the phrase "force the metals into the soluble phase".
5. Is forcing the metals into the soluble phase an example of a chemical or a physical change? Explain your answer.
6. Explain what is meant by a Chemist when he/she refers to a substance as a fuel.
7. Is natural gas defined as a renewable or non-renewable fuel? Explain your answer.
   
8. Natural gas is combusted for use as a fuel. Is this an example of chemical or a physical change? Explain your answer.
9. Write a balanced chemical equation for the complete combustion of the main constituent of natural gas.
10. Of the 3 hydrocarbons you named in question 3, which one would be considered the "best" fuel? Explain your answer.
    

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?
   

Salivary Amylase

Wheat, potatoes, corn and rice contain starch and starch is a major component of the modern diet. Amylase enzymes secreted in saliva help break down starches into simple sugar molecules that can be absorbed into the bloodstream, influencing blood glucose levels.
Monell Center scientists have undertaken a study which revealed that changes of starch consistency in the mouth were directly related to salivary amylase activity. In this study:

• saliva was collected from 73 subjects
• saliva was mixed with a standardized starch solution, and a sensor measured the enzymatic break-down of the starch's consistency
• enzyme and protein assays directly measured the amount and activity of salivary amylase in the saliva samples
• subjects completed a survey to rate the perceived breakdown of a starch sample in the mouth over a minute

Foods with different starch levels were perceived differently by people depending on how much salivary amylase they produce. "What may seem like a thick and resistant pudding or starchy food to some may seem noticeably thin in the mouths of others", said Monell sensory geneticist Paul A. S. Breslin.
Individuals who have more salivary amylase may break down starchy foods more quickly, leading to more rapid increase of post-meal blood glucose levels. It is possible that high levels of salivary amylase contribute to the risk of insulin resistance and non-insulin dependent diabetes.

Reference:
Abigail L Mandel, Catherine Peyrot des Gachons, Kimberly L Plank, Suzanne Alarcon, Paul A S Breslin. Individual Differences in AMY1 Gene Copy Number, Salivary α-Amylase Levels, and the Perception of Oral Starch. PLoS ONE, 2010; DOI: 10.1371/journal.pone.0013352

Further Reading
http://www.ausetute.com.au/enzymes.html
http://www.ausetute.com.au/sugars.html

Study Questions

1. Give a general chemical formula for starch.
2. Starch is an example of a biological polymer. Of what monomers is this polymer made up of?
3. Another biological polymer is made up of the same monomers as that of starch, but, it is found in animals instead of plants. What is the name of this polymer?
4. Assuming you were given two sample bottles, one contained the plant polymer starch, and the other contained the animal polymer in question 3. What simple test or tests could you perform to identify which bottle contained the plant polymer and which contained the animal polymer?
5. What is meant by the term enzyme?
6. Draw a diagram to represent how amylase acts on starch to produce simple sugars.
7. Assume one of the subjects in the study had a fever and was found to have a temperature of 40^oC. What effect would this have on the results obtained during the survey phase of the study?
8. Imagine a well-wisher gave our sick subject above a "nice, hot lemon drink" to relieve the fever's symptons just before the saliva sample was collected. What impact would the lemon drink most likely have on the level of amylase activity?
   

Crystal Violet Lactone

Crystal violet lactone (CVL) is known as a leuco dye.
In a basic environment, the central carbon atom of crystal violet lactone (CVL) forms 4 covalent bonds and the molecule is colourless. In an acidic environment, the lactone ring is broken and the central carbon atom gains a positive charge through the loss of a valence electron, this is the coloured form of the molecule.
These reactions are shown below:

CVL was the first dye used in carbonless copy papers.
Carbonless paper consists of sheets of paper coated with a microencapsulated dye or a reactive clay.
The back of the first sheet is coated with the dye, the top of the lowest sheet is coated with a clay that quickly reacts with the dye to form a permanent mark. When you write on the sheets, the pressure of the pen tip breaks open the micor-capsules of dye, the dye reacts with the clay, and a permanent copy is made of the document.
Chemists in Poland have also discovered that CVL molecules emit white light with continuous spectrum covering almost the entire visible range. This is an important discovery because it is known that white light from artificial sources such as fluorescent lights is devoid of many colour components and that this is responsible for causing tired eyes. Making a better artificial white light could result in improved productivity in humans.

Reference:
Jerzy Karpiuk, Ewelina Karolak, Jacek Nowacki. Tuneable white fluorescence from intramolecular exciplexes. Physical Chemistry Chemical Physics, 2010; 12 (31): 8804 DOI: 10.1039/B927232A

Further Reading
http://www.ausetute.com.au/fungroup.html
http://www.ausetute.com.au/acidbase.html

Study Questions

1. Identify the various functional groups in each of the molecules shown above.
2. Name each of these functional groups.
3. Carefully read the introductory paragraph in the story above, and study the reaction diagram. Can you circle a lactone ring?
4. Imagine you could obtain pure samples of each of the two molecules shown. In what ways would the samples be similar? In what ways would they be different?
5. Describe two tests that you could used to distinguish between each of the pure samples above.
   

Your Phone: Your Spectrometer

Professor Alexander Scheeline of the University of Illinois has developed a method to turn a mobile (cell) phone into a portable spectrometer.

In a spectrometer, white light shines through a sample solution. The solution absorbs certain wavelengths of light. A diffraction grating then spreads the light into its colour spectrum like a prism. Chemists analyze the spectrum to tell them about the properties of the sample.

In Scheeline's device, a single light-emitting diode (LED) powered by a 3-volt battery (as used in key fobs to remotely lock a car) is used as the light source. Diffraction gratings are available from scientific supply companies, as are cuvettes, the small, clear containers to hold the sample solutions. The mobile (cell) phone is used to take a photo of the spectrum obtained. Then the JPEG photo is analyzed using a software program freely accessible online:
http://www.asdlib.org/onlineArticles/elabware/Scheeline_Kelly_Spectrophotometer/index.html

Further Reading
http://www.ausetute.com.au/spectros.html

Further Activities

1. Build a spectrometer as per the instructions given in here : http://www.asdlib.org/onlineArticles/elabware/Scheeline_Kelly_Spectrophotometer/HSFiles/3.html
   
2. Follow the instructions in the preparation of a solutions of different concentrations, including a blank.
3. Record each spectrum produced by taking a photo of it.
4. Upload the photos into the programme which you should download using the link above.
5. Data will be available as an exported csv file for excel.
6. Plot absorbance versus concentration.
7. Obtain a solution of unknown concentration.
8. Use the plot above to determine the concentration of this solution.
   

Nobel Prize for Work on Graphene

The 2010 Nobel Prize in Physics has been awarded to Andre Geim and Konstantin Novoselov for their "groundbreaking experiments regarding the two-dimensional material graphene".

Graphene is an allotrope of carbon, it is the thinnest and strongest material known. It conducts electricity as well as copper and outperforms all other materials as a conductor of heat. It is almost completely transparent, yet it is so dense that not even helium, the smallest known gas atom, can pass through it.

Geim and Novoselov extracted graphene from a piece of graphite such as is found in "lead" pencils. Using a piece of adhesive tape they obtained a flake of carbon that was just one atom thick, which is the allotrope known as graphene.

Reference:
http://static.nobelprize.org/nobel_prizes/physics/laureates/2010/info_publ_phy_10_en.pdf

Further Reading
Allotropes
Elements

Study Questions:

1. What is meant by the term allotrope?
2. Name two other naturally occurring allotropes of carbon.
3. Draw a table listing the physical properties of both of these allotropes and graphene.
4. Discuss the similarities and differences between these allotropes.
5. Draw a possible structure for graphene.
6. Describe the similarities and differences between the structure for graphene that you have drawn and the structures for the other two allotropes in your table.
7. Using your structure for graphene, explain the similarities and differences between the physical properties of graphene and the other two allotropes.