24 Carat Chemistry

I was trying to buy a present for my mum for Mothers' Day. "A gold chain," I thought, "would be a nice present". But when I got to the jewellery shop I found that there is a huge variety of "gold chains", 24 carat gold, 18 carat gold, 9 carat gold, 995, 750, 375, white gold, rose gold...

So what is a carat?
What do those numbers mean?
How can "gold" be different colours?

Read all about it in the June 2019 issue of AUS-e-NEWS

Subscribe to AUS-e-TUTE's free quarterly newsletter at https://www.ausetute.com.au/ausenews.html

Methanol and the Home-Brewer

In June 2013, a young man in Queensland died as a result of drinking homemade liquor. It is believed that the liquor contained a toxic level of methanol (also known as wood alcohol). Drinking 10 mL of pure methanol can cause permanent blindness, drinking 30 mL of methanol can kill you.

The first step in the production of homemade liquors, is the fermentation of sugar.
Methanol, CH₃OH,is formed during fermentation.
When fermenting 6 kg of sugar dissolved in water for the production of distilled spirits such as whiskey or vodka, the home-brewer (and home-distiller) will typically find that the concentration of methanol in their brew is about 3 parts per million.

Many fruits are used by the home-brewer as the source of sugar to be fermented. Each fruit will lend a distinctive flavour to the final product. But fruits that are high in pectin will produce greater concentrations of methanol. Apples, apricots, guavas, quinces, plums, gooseberries, and citrus fruits like oranges, all contain high levels of pectin, typically more than 1% by mass pectin. Grapes, cherries and strawberries contain low levels of pectin, less than 1% by mass pectin.

Pectin contains  galacturonic acid which has the structural formula shown below:

In pectin, about 80% of the carboxyl groups in galacturonic acid are esterified with methanol. The remaining non-esterified carboxyl groups exist as the acid, or as salts with sodium, potassium or calcium. When pectin is broken down by enzymes during the brewing process, the methyl esters react with water to produce methanol.

The second step in the production of homemade liquor is the distillation step.
This is the crucial step in removing as much of the toxic methanol as possible.
The boiling point of methanol is about 65^oC, but the boiling point of ethanol (the desired product) is about 78^oC. During the distillation process, the first fraction collected should contain the methanol. This fraction should be collected and discarded. The next fraction should contain the desired liquor. It is highly recommended that any distillate collected after about 96^oC also be discarded.


Reference:
http://www.couriermail.com.au/news/queensland/ballandean-man-bill-lynam-who-lost-his-son-joel-to-homemade-liquor-poisoning-is-thankful-that-other-son-joshua-survived/story-fnihsrf2-1226664893229

Further Reading
http://ausetute.com.au/members/alkanolp.html (members only tutorial on alkanols)
http://ausetute.com.au/members/carboxyl.html (members only tutorial on alkanoic acids) 
http://ausetute.com.au/partspm.html 
http://ausetute.com.au/density.html 

Suggested Study Questions:

1. Draw the structural formula for methanol.
2. Locate the functional group present in methanol on the structural formula above. Name the functional group. 
3. At 25^oC methanol has a density of  0.79 g mL^-3. Calculate the mass of methanol present in a lethal dose of pure methanol .
4.  Convert the concentration of methanol given for homemade whiskey into a concentration in g mL^-1.
5. Assume the young man who died drank homemade whiskey. What minimum volume of homemade whiskey did he drink?
6. For galacturonic acid given the:
   • molecular formula
   • molar mass
7.  On the structural formula for galacturonic acid identify and name the functional groups present.
8. Draw the structure for the sodium salt of galacturonic acid.
9. Draw the structure for galacturonic acid esterified with methanol.
10. Give the molecular formula and molar mass for the structure above.
11. Apples contain about 1% by mass pectin. 10 kg of apples are to be used in the production of a homemade liquor. What mass of pectin will be present?
12. Assume exactly 100% of the carboxyl groups in galacturonic acid are esterified with methanol. How many moles of the ester are present in 10 kg of apples?
13. Write an equation representing the reaction between this ester and water to form methanol  and galacturonic acid.
14. How many moles of methanol could be produced by the break down of pectin in 10 kg of apples?
15. Assuming the young man who died had drunk this apple concoction without distilling and removing the methanol, what minimum volume of fermented apple-drink would he have had to have drunk?
16. Why do you think most countries have outlawed home-distilling?

Arsenic in Air, Hair and Water

On Saturday 20^th August 2011, the Sydney Morning Herald reported that the chemical company Orica "discharged up to 1.2 megalitres of effluent containing traces of arsenic above its environmental protection licence cap yesterday afternoon".
Arsenic is toxic, it disrupts the transport of energy within cells and metabolism. The minimal lethal dose of arsenic in adults is about 1mg per kilogram of body mass per day, but arsenic trioxide is about 500 times more toxic than pure arsenic.

The Romans used arsenic compounds, especially naturally occurring arsenic sulfides, as medicines. The Roman writer Dioscorides (40-90) wrote in De Materia Medica (Medical Matters) that arsenic sulfides could be used to treat warts and skin eruptions, but warned that the remedy could cause the patient's hair to fall out! It is believed that Agrippina used arsenic trioxide to murder her husband so that she could marry her uncle, the Emporer Claudius.
At about the same time, the Chinese were using arsenic compounds to kill flies and rodents while Indians were using them to preserve paper from attack by insects.

In medieval Europe, arsenic trioxide was being used to treat malaria, while arsenic sulfides were used to treat arthritis, asthma, tuberculosis, and diabetes.

In 1809, Dr. Fowler's Solution first appeared in the London Pharmacopoeia, and it was considered to be a cure for almost everything! Fowler's solution was a mixture of potassium arsenite in lavender water. It was prepared by dissolving 10g of arsenic trioxide and 7.6g of potassium hydrogen carbonate in 1L of distilled water, then adding a little alcohol and lavender oil. The maximum single dose recommended was 0.5mL of Fowler's Solution which could be added to a glass of water or wine.

Arsenic was very common in European households up until the late 19^th century.
Arsenic was being used to provide brilliant colours in dyes and paints:

• yellow orpiment, As₂S₃ (a mineral in use since Ancient times)
  
• red realgar, As₄S₄ (a mineral in use since Ancient times)
  
• Scheele's Green, copper arsenite, CuHAsO₃ (first produced in 1778)
• Emerald Green, a combination of copper acetate and copper arsenite (first produced in 1822)

In the 19^th century, arsenic-based green colours were being used to colour paint, wallpaper, soap, lampshades, children's toys, candles, soft furnishings, and even food. By the late 19th century, Gosio's disease, sickness resulting from breathing the air in rooms decorated with arsenic compounds, was identified. The deadly vapour was not identified as trimethylarsine until the 1930's.

Napoleon Bonaparte died on 6^th May 1821 at Longwood House on Saint Helena. Samples of Napoleon's hair were analysed in 1995 and were found to contain between 33ppm and 17ppm of arsenic, the maximum "safe" limit is currently considered to be about 3ppm and the normal level is about 1ppm. While some people believe that Napoleon was deliberately poisoned,it is possible that green furnishings at Longwood House could be to blame for the high levels of arsenic in his body.

Arsenic has also been discovered in the hair of "mad" King George III of Great Britain who died in 1820. In 2003, samples of the King's hair found in the Science Museum London were analyzed and found to contain about 17ppm arsenic.

in 1904, Julius Nieuwland added an aluminium chloride catalyst to a mixture of acetylene and arsenic trichloride to produce an arsenic compound that came to be known as Lewisite. Unfortunately Nieuwland had taken no safety precautions so he breathed in some of the vapour, was taken ill and spent the next few days in hospital. During World War I, Winford Lewis heard about Nieuwland's earlier experiment, and he learnt how to produce the toxic compound under carefully controlled conditions so that it could be used as a weapon. By November 1918, the USA was shipping deadly Lewisite to Europe. Lewisite was then used by the Japenese against the Chinese in Manchuria in 1940, and by Saddam Hussein in the Iran-Iraq war in the 1980's.

Tube wells, drilled in the 1970's in West Bengal, India and Bangladesh, were installed in a drive by the United Nations Children's Fund (UNICEF) to provide safe drinking water for a population that had traditionally taken its water from contaminated streams, rivers, and ponds, and therefore suffered from water-borne diseases such as gastroenteritis, typhoid and cholera. By 1983 the population, more than 30 million people, were showing signs of arsenic poisoning. The water in many of the wells had arsenic levels of between 50ppb and 4000ppb. At the time, the World Health Organisation (WHO) stated that drinking water should not contain more than 10μg/L.

In the 20th century, copper arsenite, also known as Paris Green, and lead arsenate have been used as a horticultural spray to kill moths on apple trees, but these compounds have now been phased out. Chromium copper arsenate, used to treat wood to prevent it rotting and being eaten by termites, has been phased out in some countries like Australia, Canada and the USA, but is still being used in others. In the electronics industries, arsenic is added to silicon and germanium semiconductors to provide electrons to the crystal lattice. Gallium arsenide is a semi-conductor which has the ability to convert electric current to laser light, so this is a growing use for the world's arsenic.

Further Reading
Volume Conversions
Parts per Million Concentration
W/V %
Molarity
Writing Ionic Formulae
Oxidation States (Numbers)

Study Questions:

1. Convert 1.2 megalitres to a volume in
   • litres
   • kilolitres
   • gigalitres
   • millilitres
2. "The minimal lethal dose of arsenic in adults is about 1mg per kilogram of body mass per day". Calculate the mass of the dose of arsenic that would be lethal in each case below:
   • 1 dose given in 1 day to a man weighing 90kg
   • 1 dose given in 1 day to a woman weighing 65kg
   • 1 dose given in 1 day to a child weighing 30kg
   • 1 dose given 3 times a day with meals to a person weighing 70kg.
3. The arsenite ion has the formula AsO₃^3- and the arsenate ion has the formula AsO₄^3-.
   • Write the formula for potassium arsenite
   • Write the formula for potassium arsenate
   • Write the formula for calcium arsenite
   • Write the formula for barium arsenate
   • Write the formula for ammonium arsenate
   • Write the formula for copper (II) arsenite
   • Write the formula for lead (II) arsenate
     
4. Give the oxidation state (number) of arsenic in each of the following:
   • AsO₃^3-
   • AsO₄^3-
   • As₂S₃
   • As₄S₄
   • HAsO₃^2-
   • As₂O₃
   • AsCl₃
5. Calculate the concentration of arsenic ions in mol/L in 1L of Fowler's Solution using the recipe provided in the article (assume all the arsenic present is in the form of arsenic ions).
6. For a 0.5mL dose of Fowler's Solution, calculate
   • the mass of arsenic present in grams
   • the mass of arsenic present in milligrams
   • the concentration of arsenic in parts per million
7. Assuming 10g hair samples were tested for arsenic
   • What is the mass of arsenic present in a healthy persons hair if the normal level is 1ppm?
   • The safe limit for arsenic in hair is 3ppm, what mass of arsenic is this equivalent to ?
   • Napoleon's hair was found to contain between 17ppm and 33ppm arsenic. Convert each of these concentrations to a mass of arsenic.
8. For the water tested in the Asian tube wells:
   • convert 4000ppb to a concentration in ppm
   • calculate the mass of arsenic in 1L of water if the concentration is 50ppb
   • convert the safe limit for arsenic in drinking water, 10μg/L, to a concentration in mol/L
   • calculate the mass of arsenic present in 1L of drinking water that contains 10μg/L arsenic
     

Reference

http://www.smh.com.au/environment/orica-admits-arsenic-spill-into-river-20110819-1j2nz.html#ixzz1Vcq8n2jf

PBDEs

Polybrominated diphenyl ethers, PBDEs, have been used as flame retardants in many common household products such as blankets, couches, food wrappers, as well as in motor vehicles and airplanes.
A diphenyl ether molecule has the following structure:

One of the polybrominated diphenyl ether compounds is 2,2',4,4',5-pentabromodiphenyl ether and it has following structure
There are 209 possible substances which are included in the family of polybrominated diphenyl ethers (PBDEs) and these are called congeners. Congeners include dibromodiphenyl ethers, tribromodiphenyl ethers, tetrabromodiphenyl ethers, pentabromodiphenyl ethers, hexabromodiphenyl ethers, heptabromodiphenyl ethers, octabromodiphenyl ethers, nonabromodiphenyl ethers and decabromodiphenyl ethers.

PBDEs with 1-5 bromine atoms per molecule are considered to be more dangerous than PBDEs with more bromine atoms per molecules because they are more efficient at accumulating in living things. In humans they effect hormone levels in the thyroid which can lead to alterations in behaviour. Studies have shown that children in developed countries have higher levels of blood PBDEs than adults, ranging from 24 to 114 parts per billion.

Most PBDEs have either been banned or are in the process of being phased out, eg,:

• Penta and octa PBDEs are no longer manufactured in the USA because of the health risks while the European Union banned their use in 2004.
• Deca PBDE has commonly been used in the electronics industry but has now been banned in Europe.

There is, however, growing concern that PBDEs may have a long environmental life.

Reference
Crystal Y. Usenko, Eleanor M. Robinson, Sascha Usenko, Bryan W. Brooks, Erica D. Bruce. PBDE developmental effects on embryonic zebrafish. Environmental Toxicology and Chemistry, 2011; DOI: 10.1002/etc.570

Further Reading
Nomenclature
Haloalkanes
Structural Isomers
Functional Groups
Percentage Composition
Parts per Million Concentration

Study Questions

1. For the diphenyl ether molecule:
   • identify the ether functional group
   • give the molecular formula
   • calculate the molecular mass (formula weight)
   • calculate the percentage composition
2. For the 2,2',4,4',5-pentabromodiphenyl ether molecule:
   • identify the ether functional group
   • give the molecular formula
   • calculate the molecular mass (formula weight)
   • calculate the percentage composition
3. How many bromine atoms would be found in a molecule of each of the following:
   
   • dibromodiphenyl ether
   • tribromodiphenyl ether
   • tetrabromodiphenyl ether
   • pentabromodiphenyl ether
   • hexabromodiphenyl ether
   • heptabromodiphenyl ether
   • octabromodiphenyl ether
   • nonabromodiphenyl ether
   • decabromodiphenyl ether
4. Draw one structural isomer of each of the molecules above.
5. Name each of the molecules you have drawn in question 4 above.
6. Give the molecular formula for the molecules you have drawn that have been considered to be the least dangerous.
7. The blood of a child is found to have 70ppb PBDE. Convert this to:
   • ppm
   • mg/g
   • g/L
8. Assuming the child above has 4.7L of blood in his/her body, calculate the mass of PBDE present.
9. In the USA, the EPA set a "safe" limit of 7 micrograms per kilogram of body weight for PBDE. If the child above has a mass of 18kg, is the amount of PBDE in his/her blood considered safe? Explain your answer.
   
   
   
   

Lithium for a Longer Life

Lithium is the 25^th most abundant element in the Earth's crust, with approximately 20mg of lithium present in every kilogram of crustal material. It is a soft, silvery-white metal that belongs to Group I (alkali metals). It is so highly reactive that when it is cut in air it will quickly corrode before your eyes. In the presence of water, lithium reacts to form hydrogen gas and lithium hydroxide in aqueous solution. Because it is so reactive, lithium does not occur free in nature, it only appears naturally in compounds.

Lithium-6 and lithium-7 were among the three elements synthesized in the Big Bang according to cosmological theory, the other two elements being hydrogen and helium. Lithium is present in cooler, less massive brown dwarf stars but is destroyed in hotter red dwarf stars, so its presence in the stars' line emission (atomic) spectra can be used to differentiate between these two kinds of stars in the so-called 'lithium test'.

Trace amounts of lithium ions are present in the oceans. The total lithium content of seawater is estimated to be 230 billion tonnes, and is present in concentrations of about 0.2 parts per million.
Lithium is also present in trace amounts in plants and animals. Vertebrates contain lithium in concentrations between 21 and 763 parts per billion.

Lithium salts, such as lithium carbonate, have been to shown to be useful as mood-stabilizing drugs. Therapeutically useful amounts of lithium are between 1.0 and 1.2 millimolar, which is only slightly lower than the toxic amount of 1.5 millimolar.

Scientists at the Friedrich Schiller University Jena have just demonstrated that a regular uptake of lithium could lead to a longer life. The scientists studied the impact of lithium in a concentration that is regularly found in ordinary tap water by analyzing the mortality rate in 18 adjacent Japanese municipalities in relation to the amount of lithium contained in tap water from the respective regions. They found that the mortality rate was considerably lower in those municipalities with more lithium in the drinking water.

Reference
Kim Zarse, Takeshi Terao, Jing Tian, Noboru Iwata, Nobuyoshi Ishii, Michael Ristow. Low-dose lithium uptake promotes longevity in humans and metazoans. European Journal of Nutrition, 2011; DOI: 10.1007/s00394-011-0171-x

Further Reading
Elements and Compounds
Metals and Non-metals
Trends in Group I
Electron Configuration
Naming Ionic Compounds
Writing Ionic Formulae
Parts per Million Concentration
Molarity Concentration
Emission (Atomic) Spectra
Isotopes
Relative Atomic Mass

Study Questions

1. What is the atomic number of lithium?
2. What is the simple electron configuration for an atom of lithium?
3. What is the expected charge on a lithium ion? Explain your answer.
4. Write the formula for each of these compounds:
   
   • lithium hydroxide
   • lithium carbonate
5. Write a balanced chemical equation to represent the reaction between lithium metal and water.
6. For each of the following isotopes of lithium, give the number of protons and the number of neutrons present:
   
   • lithium-6
   • lithium-7
7. Given that the relative atomic mass of lithium is 6.941, and assuming lithium-6 and lithium-7 are the only isotopes of lithium present, calculate the abundance of each isotope.
8. Convert the following to concentrations in molL^-1 (M):
   
   • 0.2ppm
   • 1.2millimolar
   • 1.5millimolar
     
   • 21ppb
   • 763ppb
9. If the total lithium content of seawater is estimated to be 230 billion tonnes, and is present in concentrations of about 0.2 parts per million, what is the mass of seawater present on Earth?
10. In the 'lithium test' for stars, what spectral lines do you expect to see in brown dwarf stars that will not be present in red dwarf stars?