Lucapa Diamond

The Perth-based Lucapa Diamond Company found a 404 carat diamond at its mine in Angola, a republic in southern Africa. It is the biggest diamond found to date in Angola and has been valued at about $20 million.

The mass of gemstones such as diamonds is measured in carats. 1 carat equals 200 mg.
1 carat is subdivided into 100 points, so a point is equal to a mass of 2mg.

Diamonds form at depths of 150 - 200 km in the upper mantle where temperatures range from 900 to 1300^oC and the pressure is about 50,000 times atmospheric pressure. Under these extreme conditions, carbon atoms come together to form the diamond structure in which each carbon atom makes 4 covalent bonds to other carbon atoms. In the diagram shown, each black ball represents a carbon atom and each line represents a covalent bond.

Diamonds are brought to the earth's surface from the upper mantle  in a dyke which geologists refer to as a kimberlite pipe.

 The density of naturally occurring diamonds varies between 3.15 and 3.53 g cm^-3, with the purest diamonds having a density closer to 3.52 g cm^-3.
Type I diamonds include diamonds in which nitrogen is present as an impurity. A colourless Type 1 diamond has very little nitrogen impurity. As the amount of nitrogen present increases, the diamond becomes more yellow.
Type II diamonds have  no measurable nitrogen impurity. The Lucapa diamond is a Type II diamond and is colourless because it contains no measurable nitrogen or other impurity, and, the structure has not been changed significantly from the "pure" diamond structure shown above during formation.
Some Type II diamonds are coloured pink, red or brown as a result of changes to the structure of the diamond during formation so that light is scattered in such a way as to produce these colours.
The presence of boron as an impurity results in a light blue coloured diamond, whereas the presence of black impurities such as graphite or sulfides produces a black diamond.
The presence of measurable quantities of hydrogen as well as structural changes during formation can result in purple diamonds.


Reference:
http://www.abc.net.au/news/2016-02-15/giant-diamond-found-in-angola-by-wa-company-lucapa/7168974


Further Reading:
Mass Conversions
Density
Allotropes


Suggested Study Questions:

1. Convert 200 mg to a mass in
   • grams
   • kilograms
   • micrograms
2. The diamond found at Lucapa is reported to be a 404 carat diamond. What is the mass of this diamond in
   • grams
   • kilograms
   • micrograms
3.  The value of the Lucapa diamond is estimated to be $20 million. What is the value of the diamond:
   • per carat
   • per point
   • per milligram
   • per gram
4. Assuming the Lucapa diamond to be a pure diamond, its density is 3.52 g cm^-3 . What is the volume of this diamond? 
5. Imagine pouring 500 mL of water in a 1000 mL measuring cylinder at 101.3 kPa and 25 ^oC, then dropping the Lucapa diamond into the water. What would the new volume of water be in the measuring cylinder? (assume the density of water is 1 g cm^-3)
6. Coal is also made up largely of carbon atoms, with tiny amounts of oxygen and impurities such as sulfur.  It is usually found as a vein or seam of coal within sedimentary rocks. Coal has an average density of about 1.2 g cm^-3. If a lump of coal had the same volume as the Lucapa diamond, what would its mass in grams be?
7. Given the difference in the density of diamond and the density of coal, what does this tell you about the structure of diamond and coal?
8. If you were given 5 grams of coal and 5 grams of diamond, which would have the greatest volume?
9. Draw a diagram to represent the 3-dimensional structure of diamond. On your diagram:
• draw a red line to indicate a covalent bond
• use a blue pencil to show a carbon tetrahedron
• use a black pencil to show one carbon-carbon bond angle
10. What is the angle between two adjacent carbon atoms in the diamond structure?

Salts of Drugs a Health Risk

Many studies have shown that excess salt is harmful to heart health, but many commonly prescribed medicines have sodium added to improve their absorption into the body, but the effect of doing this has not been known. For example, 1 Alka-Seltzer tablet contains 324 mg of aspirin (the drug) and 445 mg of sodium.
University of Dundee and College of London researchers have found that a person taking the maximum, daily dose of some medicines would exceed the recommended daily dietary intake limits for sodium. In Australia, the total maximum recommended limit of sodium for adults should be less than 2300 mg per day (less for children). The label on the Alka-Seltzer tablets carries a warning that you should not take more than 8 tablets per day.
In the study, the researchers found that patients taking the sodium-containing medication had a 16% increased risk of a heart attack, were 7 times more likely to develop high blood pressure, and, were 28% more likely to die, compared with patients who took the non-sodium containing versions of the same drug.

So why do we add sodium to drugs if it is potentially harmful?

We do this because many drugs are actually insoluble in water. The cells in your body are made up mostly of water, so if you want to be able to transport a drug around the body, and have it absorbed into cells, it is beneficial if the drug is soluble in water.

How do we add sodium to drugs?

If the drug is, for example, a weak acid like aspirin, then it is not very soluble in water.
Being a weak acid, though, aspirin can undergo a proton transfer (neutralisation) reaction with a base such as sodium hydroxide. The product of a neutralisation reaction are salt and water.
acid + base → salt + water

aspirin + sodium hydroxide → sodium salt of aspirin + water

The sodium salt of aspirin readily dissolves in water by dissociating into positive sodium ions and negative "aspirin" ions.


Reference:
BMJ-British Medical Journal (2013, November 26). High salt levels in medicines increase risk of cardiovascular events. ScienceDaily. Retrieved November 28, 2013, from http://www.sciencedaily.com­ /releases/2013/11/131126191557.htm 

Further Reading
aspirin
mass conversions 
ppm
molarity
neutralisation
proton transfer reactions
acid dissociation constants

Suggested Study Questions: 

1. Convert these masses in milligrams to masses in grams
• 324 mg
• 445 mg
2. The label on the Alka-Seltzer packet recommends dissolving 2 tablets in water. For these two tablets, calculate the mass in milligrams of
• aspirin
• sodium
3. If you were to take the maximum number of tablets, 8, in a day, how much of each of the following substances would you be ingesting?
• aspirin
• sodium
4. Would you be exceeding the recommended daily dietary intake limits for sodium in Australia? Explain your answer.
5. A low salt food is one that contains less than 120 mg of sodium per 100 g of food. If Alka-Seltzer were to be considered a low salt food, what would the mass of each tablet need to be?
6. Aspirin has the molecular formula C₉H₈O₄. What is the molar mass of aspirin?
7. The sodium salt of aspirin has the molecular formula C₉H₇O₄^-Na⁺. What is the molar mass of the sodium salt of aspirin?
8. Calculate the mass of sodium in 1 Alka-Seltzer tablet due to the sodium salt of aspirin.
9. Compare the mass of sodium calculated above to the actual mass of sodium present in 1 Alka-Seltzer tablet according to the package. How would you explain the difference in the two masses?
10. If a person dissolved 2 Akla-Seltzer tablets in 150 mL of water, what is the concentration of sodium ions in the water in
    • mol/L
    • mg/L
    • ppm
11. Recommendations for the daily intake of potassium are higher than those for sodium at 4700 mg day, so one way to alleviate the sodium problem in aspirin tablets might be to replace the sodium with potassium. Describe one way that you could produce the potassium salt of aspirin.

 

Phlogiston Theory

Before the modern chemical ideas of atoms and elements, phlogiston theory was a widely held belief.
According to phlogiston theory, matter consisted of three essential essences:

• sulfur (terra pinguis - the essence of inflammability, which was to become known as phlogiston)
• mercury (terra mercurialis - the essence of fluidity)
• salt (terra lapida - the essence of fixity and inertness)

 Phlogiston theory was an early attempt to to try to explain what happened when things were burnt or combusted. In phlogiston theory, substances were made up of a "calx" (or residue) combined with phlogiston (the essence of inflammability). When a substance was burnt (combusted), phlogiston was released, and the residue (calx) was left behind. Even the rusting of iron could be explained using phlogiston theory, because the "iron" would lose its phlogiston during the rusting process and leave behind the "calx" or residue. One of the problems with the phlogiston theory is that metals should lose mass when they burn, owing to the loss of phlogiston.

In the 18th century, Antoine-Laurent de Lavoisier, the man who is considered to be the father of modern of modern chemistry, conducted a series of combustion experiments. In these experiments he carefully weighed the substances to be combusted as well as the products of combustion, and found that the weight of the products of combustion was greater than the weight of the substance before combustion. He also demonstrated that when a substance corrodes in a sealed container, the gain in weight of the substance is equal to the loss in weight of the air in the container.
This was the beginning of the downfall of the phlogiston theory, but it was the beginning of the modern chemistry when Lavoisier generalized that if the weights of all substances involved in a chemical reaction are considered then there is no overall loss or gain in weight.

Further Reading:
http://www.ausetute.com.au/elemhist.html
http://www.ausetute.com.au/elements.html
http://www.ausetute.com.au/atomichist.html
http://www.ausetute.com.au/wriiform.html
http://www.ausetute.com.au/namiform.html
http://www.ausetute.com.au/namcform.html
http://www.ausetute.com.au/balcheme.html

Suggested Study Questions

1. Lavoisier burnt sulfur. When sulfur burns in air, it reacts with oxygen to form sulfur dioxide. Write a word equation for this reaction.
2. Write the chemical formula for each of the following:
   • sulfur
   • oxygen gas
   • sulfur dioxide gas
3. Write a balanced chemical equation for the combustion of sulfur to produce sulfur dioxide gas.
4. If Lavoisier had weighed out 32 grams of sulfur and then burnt it in air, the sulfur dioxide he collected would have a mass of 64 grams. What mass of oxygen would have been reacted with the sulfur? 
5. Explain why a substance such as sulfur appears to gain mass when it is combusted.
6. When wood is burnt, the mass of the ashes left behind is actually less than the mass of wood you started with. How do you explain this loss of mass?
7. Magnesium is a metal that combusts readily in oxygen gas to form magnesium oxide.
   • Write a word equation for the combustion of magnesium to form magnesium oxide,
   • Write a balanced chemical equation for this reaction.
8. If 20.16 grams of magnesium oxide is produced as a result of the combustion of 12.16 grams of magnesium, how much oxygen gas was consumed during the reaction?
9. Imagine you are living in the 18th century and that you are a firm believer in the phlogiston theory. How would you explain to Lavoisier how metals gain mass when they burn?