2013 Chemistry Calendar

The quintessential Chemistry Calendar for 2013 is now available to download for free at AUS-e-TUTE

Now there's no excuse for not celebrating the birthday of significant Chemists!

Gallium Practical Jokes

If you ask a Chemist what their favourite metal is, the chances are they will answer gallium.

Historically, gallium is significant because it was one of the elements that Dmitri  Mendeleev predicted the properties of, before the element had even been discovered! Mendeleev called the element ekkaaluminium.

Gallium has gained commercial value because gallium compounds such as gallium arsenide, GaAs, are important semiconductors in the electronics industry.

But the reason many Chemists like gallium is because of its interesting physical properties.
Gallium is a silvery metal with a metallic lustre that looks a lot like silver. Unlike silver however, gallium is not found as the element in nature. Gallium compounds occur in minute quantities in bauxite (an aluminium ore) and sphalerite (a zinc ore) and can be extracted from these ores by smelting.
The melting point of gallium is about 29.8^oC and its boiling point is about 2204^oC. This means that at temperatures between 29.8^oC and 2204^oC gallium is a liquid. Or put another way, if you have some gallium in a test tube on a hot summer's day in Sydney, or Miami, or anywhere where the temperature gets above 30^oC, what you will see is a puddle of molten metal, but if you take the molten gallium back into an air-conditioned room where the temperature is likely to be less than 25^oC, the gallium will freeze again.
And this is the basis of the disappearing spoon trick as shown in the video.

At temperatures below its melting point, gallium is a solid and can be fashioned into a spoon shape.  Being a silvery, metallic metal, it looks just like a silver teaspoon. However, if you were to stir your cup of hot tea or hot coffee with the gallium spoon, the spoon will melt because the temperature of the tea or coffee will be above the melting point of the gallium.



Further Reading
History of the Periodic Table
Periodic Table of the Elements
Metals and Non-metals
Chemical and Physical Changes
Writing Ionic Formula
Naming Ionic Compounds
Temperature Conversions
Latent Heat

Suggested Study Questions

1. Use the Periodic Table to find the following for gallium:
   • symbol
   • atomic number
   • atomic mass
2. With reference to the Periodic Table explain why Mendeleev would have named the unknown element, located where gallium is now known to be, ekkaaluminium.
3. Gallium often occurs in compounds in the +3 oxidation state, or as an ion in salts with a charge of 3+. Give the most likely formula for each of the following:
   • gallium chloride
   • gallium oxide
   • gallium hydroxide
4. Give the most likely name for each of the following:
   • GaH₃
   • Ga(NO₃)₃
   • Ga₂(CO₃)₃
5. Does the video show a chemical or a physical process? Explain your answer.
6. Sketch a temperature vs time curve to describe the melting of gallium.
7. Convert the melting point and boiling point of gallium from centigrade to kelvin.
8. Mercury has a melting point of about 234K and a boiling point of around 630K. Convert these temperatures to ^oC
9. Explain why mercury is a liquid at room temperature and pressure.
10. Could you freeze mercury by walking into an air-conditioned room like you can gallium? Explain your answer.

AUS-e-NEWS

An accident led to the discovery of gold in Australia's desert in 1893.

Within months a township grew up in the desert around the gold deposit.

A few years later, a scientific discovery led to a second gold rush which caused the inhabitants to destroy their town!

Read more in the December 2012 edition of AUS-e-NEWS.

If you would like to subscribe to AUS-e-NEWS email

New Metallurgy Resources

AUS-e-TUTE has just added new metallurgy resources.
Tutorials, game, test and drills on the chemistry of deciding how to extract a metal from its ore.
Visit http://www.ausetute.com.au

Paraquat

On Monday 12th November 2012, a Queensland farmer was out spraying paraquat, one of the most widely used herbicides (weedkillers) in the world. The pressure pump unit released and sprayed paraquat into the farmer's mouth. Tragically, 24 hours later the farmer died.


Because paraquat is a highly toxic chemical, it is available in Australia and the United States only to trained users and is not supplied for home or garden use. Even though it is so toxic to humans, it is still widely used because it kills a wide range of grasses and weeds very quickly and becomes biologically inactive on contact with the soil.

Paraquat is the trade-name for 1,1'-dimethyl-4,4'-bipyridinium dichloride. The structural formula is shown on the right.
1,1'-Dimethyl-4,4'-bipyridinium dichloride is a yellow solid at room temperature and pressure and smells faintly like ammonia.

 Commercially, paraquat is available as a solution at a concentration of 250 g/L. This is further diluted by the farmer before applying it to the fields.


Reference
http://www.couriermail.com.au/news/queensland/lifelong-farmer-dies-from-toxic-weedkiller/story-e6freoof-1226517724826

Further Reading 
Empirical and Molecular Formula 
Relative Molecular Mass
Concentration of Solutions (molarity)
Structural Isomers

Suggested Study Questions:

1. Give the molecular formula for paraquat.
2. Give the empirical formula for paraquat.
3. Calculate the molecular mass of paraquat.
4. Calculate the moles of paraquat present in 8 L of commercially available paraquat solution.
5. Draw the structural formula for 2 possible structural isomers of paraquat.
6. Paraquat is often sold as the chloride salt as shown in the structural formula in the article above. It can also be sold as the sulfate salt. Draw a possible structural formula for the sulfate salt form.
7. In the instructions for use, the manufacturer of paraquat stresses that only clean water, water free of clay or silt, should be used to dilute the paraquat solution. Why is it so important to use clean water?
8. Suggest some safety precautions that farmers should take when preparing and using paraquat.

New Metallurgy Resources

AUS-e-TUTE has just added new tutorials, games, tests, and drills to its metallurgy section.
The new sections include:
Metal + Water Reactions
Metal + Non-oxidizing Acid Reactions
Metal + Oxygen Gas Reactions
Activity Series (metals)

Chemistry in Eclipses

The 14th November 2012 excites students of physics and those interested in astronomy. This is the date of a total eclipse of the sun. The area of totality will pass over northern Australia, from east of Darwin in the Northern Territory to the Cape York Peninsula of Far North Queensland, turning morning into darkness. The rest of Australia will see a partial eclipse.

But why would chemists get excited about a solar eclipse?

The story begins more than 200 years ago ...

Gaps in the Solar Spectrum?

In 1802 an English Chemist, William Hyde Wollaston, was the first person to record the appearance of a number of dark lines in the emission spectrum of light from the sun.

In 1814, German physicist Joseph von Fraunhofer began measuring the wavelengths of over 570 of these lines.

Fingerprinting the Sun

Robert Gustave Kirchhoff and Robert Bunsen, developed a better prism-based spectroscope and observed that the spectral lines emitted by a gas occurred at the same wavelength as the absorption lines observed when incandescent light from Bunsen's burner shone through the same gas heated at the same temperature.

Then Kirchhoff,  proposed the laws of spectroscopy which bear his name:

1. A hot solid object produces light with a continuous spectrum
2. A hot tenuous gas produces light with spectral lines at discrete wavelengths (an emission spectrum)
3. A hot solid object surrounded by a cooler tenuous gas produces light with an almost continuous spectrum with gaps at discrete wavelengths (an absorption spectrum)

A star, like the sun, will create an absorption line spectrum because the continuous spectrum emitted by the dense, opaque gas that makes up most of the star passes through the cooler, transparent atmosphere of the star.

In 1859, Kirchhoff  demonstrated that all pure substances display their own characteristic spectrum, so it is possible to use the spectrum of elements to identify elements in a mixture, just like each person's fingerprints are unique and can be used to identify them. He proposed  that the lines in the solar spectrum are caused by the absorption of light by elements in the solar atmosphere and set out to identify the elements present in our sun.

New Element Discovered

On the 18th August 1868 there was a total solar eclipse. In India, French astronomer Pierre Janssen observed this eclipse using a spectroscope. He recorded a bright yellow line with a wavelength of 587.49 nm in the spectrum of the solar prominences. The same result was also recorded by British astronomer Norman Lockyer. This line could not be due to sodium, because although sodium produces a bright yellow line (actually more than 1), the wavelength of sodium's 'line' is about 589.3 nm. Lockyer proposed that this line was due to a new element which he called helium after the greek word 'helios' meaning 'sun'.

About 10 years later, Scottish chemist William Ramsay isolated helium on earth ...... but that's another story.

References:

http://eclipse.aaq.org.au/

http://www.csiro.au/en/Outcomes/Understanding-the-Universe/Tracking-spacecraft/History-of-total-solar-eclipses.aspx

Further Reading:

Emission Spectra 

Suggested Study Questions:

1. speed of light (m/s) = frequency (s^-1) x wavelength (m)
   If the speed of light is 3 x 10⁸ ms^-1 calculate:
• find the frequency of the 'yellow line' in sodium's spectrum
• find the frequency of the yellow line for the new element found in the solar spectrum
2.  speed of light (m/s) = frequency (s^-1) x wavelength (m)
   If the speed of light is 3 x 10⁸ ms^-1 calculate:
• wavelength of blue light with a frequency of 6.9 x 10¹⁴ s^-1
• wavelength of red light with a frequency of 4.6 x 10¹⁴ s^-1
  
3. The energy of light emitted, E, is Planck's constant,h, multiplied by the speed of light divided by the wavelength of light emitted. Write a mathematical equation to represent this.
4. Use your equation above to calculate
   • energy of the blue light in question 2 above
   • energy of the red light in question 2 above
5. Complete the following generalizations:
   • The longer the wavelength of light, the ___________ energy it has
   • The shorter the frequency of light, the _________ energy it has.
6. Compare the wavelength of the 'yellow line' in sodium's spectrum and the yellow line for the 'new element'. Which element has
   • the longest wavelength
   • the shortest frequency
   • the most energy
7. Describe the difference in the spectrum of light from the sun as seen in a spectroscope compared to the spectrum of light from a fluorescent light as seen in a spectroscope.
8. Explain the differences between the two spectrum in question 7 above.

Glow in the Dark Ice

No (chemistry) party is complete without edible "glow in the dark" ice cubes.
To make your ice cubes:

•  open up some tonic water (or a bottle of "bitter lemon")
• pour it into an ice cube mold
• place the mold in the freezer until the tonic water solidifies (freezes)

To make your ice cubes glow in the dark:

• place some ice cubes in a glass of water (or cordial or carbonated beverage)
• place the glass under a UV ("black") light (even strong fluorescent light will work but the effect is not as dramatic!) and turn off the room's lights

Results : your glass of water and ice should glow a nice blue colour.


This is an example of fluorescence, the emission of light by a substance that has absorbed electromagnetic radiation. In the case of the tonic water, there is a compound in the tonic water that absorbs light in the ultraviolet region of the electromagnetic spectrum (wavelength ~ 350 nm), and emits light in the visible region of the electromagnetic spectrum (wavelength ~ 450 nm corresponding to bright blue or cyan).

The compound in the tonic water that fluoresces is known as quinine, with the molecular formula C₂₀H₂₄N₂O₂ and the structural formula shown below:

Quinine occurs naturally in the bark of the cinchona tree which is found in the tropical Andes forests of western South America. Quinine was the first effective treatment for malaria. The first medicinal uses involved drying the bark of the cinchona tree then grinding it into a powder which was then mixed into a drink (often wine), which was then drunk. The effective medicinal ingredient of the bark, quinine, was finally isolated in 1820 by French researchers Pierre  Joseph Pelletier and Joseph Bienaime Caventou.
During World War II, the Axis Powers had control over most of the commercial quinine production centres, so the Allied Powers were cut off from their supply of quinine, a necessary war-time commodity for fighting in the tropics. Then in 1944, the American chemists R.B. Woodward and W.E. Doering succeeded in producing quinine in the laboratory.




Quinine is no longer recommended as a first-line treatment of malaria, instead another plant-derived organic compound is used, artemisinin, but that's a different story.

Further Reading:
Emission Spectroscopy
Empirical Formula
Relative Molecular Mass (molecular weight, formula mass, formula weight)
Percent Composition
Parts per Million Concentration
Functional Groups


Suggested Study Questions:

1. Draw a diagram to describe what happens when quinine absorbs UV light and emits bright blue/cyan light.
2. Imagine you were to view the light emitted by the tonic water through a spectroscope. Draw a sketch of the emission spectrum you would expect to see.
3. Use the molecular formula for quinine to find its empirical formula.
4. Calculate the relative molecular mass (molecular weight, formula mass, formula weight) of quinine.
5. Calculate the percentage of each element present in quinine.
6. Assume a 1L bottle of tonic water contains 15ppm quinine. Calculate the
   • mass of quinine contained in the bottle
   • moles of quinine in the bottle
   • quinine concentration in mol L^-1
7. Using the structural formula for quinine, identify an aliphatic double bond (that is, a double bond that does not occur in an aromatic ring), an aromatic (benzene) ring, and an hydroxyl group

Nobel Prize in Chemistry 2012

The Nobel Prize in Chemistry 2012 was awarded jointly to Robert J. Lefkowitz and Brian K. Kobilka "for studies of G-protein-coupled receptors"

The cells in our bodies need to work together, they need sensors to be able to sense what is going on around them. The sensors on the surface of cells are call receptors.

The G-protein-coupled receptors are a family of receptors for adrenalin (epinephrine), dopamine, serotonin, light flavour and odour. A lot of medications that we take act on these receptors.
While these G-protein-coupled receptors are clearly very important, scientists haven't really known very much about how they work until recently.

In 1970 Lefkowitz  announced the discovery of an active receptor. Using radioactive tracers his research group examined how adrenergic receptors, receptors for adrenalin and noradrenalin, work.
In the 1980's his research team started work on trying to find the gene code for the beta receptor in the hope that this would give them clues about how the receptor works.
Kobilka joins the team and has an idea that it makes it possible to isolate the gene.
The receptor is found to consist of 7 long fatty spiral strings (helices).
A different receptor, the light receptor rhodopsin in the retina of the eye, has also been found to be made up of  7 stringed helices.

The groundbreaking discovery was that these two receptors are related even though they have different functions, that is, there is a family of receptors that look alike and function in a similar, yet different, manner.

In 2011 Kobilka and his research team finally got an image of the receptor at the very moment when it transfers the signal from the hormone on the outside of the cell to the G-protein on the inside of the cell.

Reference:
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/2012/popular-chemistryprize2012.pdf

Nobel Prize countdown

As students head back to the class room for a new term of exciting learning, the scientific community is gearing up for a major annual event, the announcement of the Noble Prizes.
With just days to go before the Nobel Prize in Chemistry is to be announced, there is much discussion (and possibly even a bit of betting) about who is likely to be this year's laureate.

Among the contenders this year are:

• Louis E. Brus (Columbia University) for the discovery of colloidal semiconductor nanocrystals (quantum dots)
• Akira Fujishima (University of Tokyo) for the discovery of photocatalytic properties of titanium dioxide (the Honda-Fujishima Effect)
• Masatake Haruta (Tokyo Metropolitan University) and Graham J. Hutchings (Cardiff University) for their discoveries of catalysis by gold

Quantum dots are semiconductors, but their electronic properties are related to the size and shape of the individual crystals. In general, the smaller a crystal is, the more energy is needed to excite the dot, which means that more energy is released when the crystal returns to its ground state. It is hoped that quantum dots will lead to practical quantum computing and increase the efficiency of photovoltaic cells. Quantum dots are being used in preference to some dyes in biological analyses because quantum dots are brighter and more stable.

While working on his Ph.D in 1967, Akira Fujishima exposed a titanium dioxide electrode to strong light and discovered that this catalyzed the decomposition of water into hydrogen and oxygen. This became known as the Honda-Fujishima Effect (Professor Kenichi Honda was Akira Fujishima's supervisor). Finding cheap, effective methods for providing hydrogen would enable the development of hydrogen as fuel.

In the 1980's Masatake Haruta showed that colloidal gold, gold clusters with diameters of 5 nanometers or less, could catalyze reactions involving oxygen gas.
Graham J Hutchings has extended the number of reactions  we now know of that can be catalyzed by gold. Hutchings has shown that primary alcohols can be oxidized to aldehydes using a gold-palladium/titanium dioxide combination without the need for a solvent. He has also developed the rapid synthesis of hydrogen peroxide, H₂O₂, from hydrogen and oxygen  without the formation of water as a by-product.

More Electrochemistry Resources

New teaching and learning resources have been added to AUS-e-TUTE on the following topics:

• Batteries (student learning resources)
• Lead-Acid Battery Case Study (student learning resources) 
• Fuel Cells (student learning resources) 
• Electrical Energy Calculations (student learning resources)
• Half-equations for Ions (teaching resources)
• Redox Reaction Concepts (teaching resources)
• Standard Electrode Potentials for Oxidation and Reduction Reactions (teaching resources)

Become an AUS-e-TUTE member and get the full benefit of using teaching and learning resources developed by experienced science teachers.
Visit http://www.ausetute.com.au.com.au to find out more.

            

Green Hair

Imagine you are living in a small town in Sweden.
You go to bed one night, naturally blonde.
When you wake up in the morning and look in the mirror your blonde hair has turned green!
Not only that, but your naturally blonde neighbour also has green hair!

This actually did happen in 2011, and, no doubt, caused a certain amount of distress.

Where would you begin in order solve the "green hair" mystery?
What could turn hair green?

Blonde hair often turns green after swimming in chlorinated pool water.
Copper, used in compounds to reduce algae growth in water, can be present in concentrations of about 0.5 ppm in pool water. When bleach (often sold as "liquid chlorine") is added to the pool water it oxidizes the copper resulting in a pretty green colour, and the oxidized copper binds to the proteins in the hair.
If you happen to have copper pipes in your bathroom, you've probably seen "green stains" on the pipes where the copper has been oxidized.

So, back to the story in Sweden.
Samples of drinking water were taken from a number of homes in order to measure the amount of copper present but the concentration of copper in the water did not exceed the recommended guidelines (that is, the copper ion concentration was less than 1 ppm).

However, in new houses, when hot water was left overnight and tested the next morning, the concentration of copper in the water increased dramatically. On further investigation it was discovered that the hot water pipes in new houses lacked the coating that the pipes in older houses had. So, overnight, when the water in the pipes was still and not being continuously "flushed" through the pipes, copper particles were being added to the water.

For solving the "Swedish Green Hair Mystery" Johan Pettersson was rewarded with a 2012 Ig Nobel Prize for Chemistry.


References:
http://www.thelocal.se/37994/20111217/
http://www.improbable.com/ig/winners/#ig2012

Further Reading 
http://www.ausetute.com.au/waterana.html 
http://www.ausetute.com.au/aas.html 
http://www.ausetute.com.au/partspm.html 
http://www.ausetute.com.au/concsols.html 
http://www.ausetute.com.au/weightpc.html 
http://www.ausetute.com.au/corrosion.html 

Suggested Study Questions:

1. Describe 2 methods you could use to detect the presence of copper ions in water.
2. Describe the process by which Atomic Absorption Sepctroscopy (AAS) could be used to measure the concentration of copper ions in a water sample.
3. Describe a way that you could prevent copper from entering the water in the copper water pipes in this Swedish town.
4. Copper is often present in soils at a concentration of around 50 ppm. What mass of copper would be present in 0.5 tonne of soil?
5. A particular pool contains 40,000 L of water. If the pool water contains 0.5 ppm copper ions, what is the concentration of copper ions in mol L^-1 ?
6. Chocolate can contain 10 mg/kg  copper. What mass of copper is present in a 250 g bar of chocolate?
7. Doses of copper that exceed 50 mg/kg of body mass can be lethal. Calculate the mass of copper that would be the lethal limit for an 80 kg adult.
8. What advice could you give the inhabitants of this Swedish town in order for them to avoid having green hair?

How many elements can be made?

Since the 1940's scientists have been synthesizing new elements with atomic numbers greater than 92, the so-called transuranium elements.

Just how many elements can we make?

Read more in the September 2012 edition of AUS-e-NEWS.

Not an AUS-e-NEWS subscriber? Email us for your free quarterly AUS-e-NEWS newsletter.

Sticking Non-stick Surfaces Together

Polymers made up of non-polar, or only very slightly polar, functional groups are said to have low surface energy and poor adsorption which means that the surfaces are not "sticky".
Teflon (polytetrafluoroethylene or PTFE) is an example of a polymer with a very low surface energy, so low that it is used to provide non-stick coatings to things like pots and pans.
Silicones (polysiloxanes), with the general formula [R₂SiO]_n in which R is an organic group such as a methyl or ethyl group, also tend to have low surface energies. Because most materials do not adhere to, or stick to, silicones, silicones have become widely used to make flexible "rubber" molds.

So, how do you join together materials like these that are not "sticky"?

This is the question that scientists at Kiel University in Germany have been studying, and the solution they have devised is to use nano-scaled crystal linkers as internal staples. These staples are made of zinc oxide in which the crystals are shaped like tetrapods, that is, each staple has 4 legs. Zinc oxide crystals are sprinkled evenly onto a heated layer of teflon. Then a layer of silicone is poured on top. The material is then heated to 100^oC for less than an hour in order to join the materials firmly together.When the zinc oxide crystals are heated, the tetrapods pierce the teflon and silicone materials, sink into them and get anchored.
Peeling the teflon layer off the silicone layer held together by the tetrapod staples is about the same as peeling sticky tape off glass.

Reference:
X. Jin, J. Strueben, L. Heepe, A. Kovalev, Y.K. Mishra, R. Adelung, S.N. Gorb, A. Staubitz. Joining the un-joinable: Adhesion between low surface energy polymers using tetrapodal ZnO linkers. Advances Materials, 2012 DOI: 10.1002/adma201201780

Further Reading
Polymers and Polymerization
Functional Groups
Molecule Polarity

Suggested Study Questions:

1. Define the term polymer
2. Give two examples of polymers that are commonly used in households.
3. Define the term functional group and give three exaples.
4. Explain what is meant by a polar functional group and a non-polar functional group.
5. Give the structural formula for the monomer that can be used to form teflon.
6. Are the bonds in the monomer you have drawn in question 5 polar or non-polar bonds. Explain your answer.
7. Is the molecule that is the monomer in question 5 polar or non-polar. Explain your answer.
8. Given the general formula for silicones provided in the article, write the formula for:
   • polydimethylsiloxane
   • polydiethylsiloxane
9. Give a possible structural formula for the monomer used to produce each of the silicone polymers in question 8.

New Electrochemistry Resources

AUS-e-TUTE has just updated its Faraday's Laws of Electrolysis and added new resources for Q = It and E=QV calculations.

A "draft" of the VCE 2013-16 chemistry syllabus study guide has also been added.

Visit http://www.ausetute.com.au to view these resources.

New Electrochemistry Resources

AUS-e-TUTE has been updating its electrochemistry section.
The latest additions have been tutorials, games, tests, exams and drills on the following topics:

• Strength of Electrolytes
• Galvanic (Voltaic) Cell Diagrams
• Electroplating Concepts

Periodic Table Teaching Resources

AUS-e-TUTE has downloadable resources related to the teaching and learning of Periodic Table concepts.

Visit http://ausetute.com.au/downloads.html to download:

• Interactive Periodic Table (only for Windows)
• Lesson Outlines for teaching Periodic Table concepts (designed to be used with AUS-e-TUTE's interactive Periodic Table)

AUS-e-TUTE Update July 2012

AUS-e-TUTE's electrochemistry resources are currently being updated.

This has resulted in a major revision of most of the resources relating to the concepts of electrochemistry.

Below is a list of the new and updated resources that have recently been added to AUS-e-TUTE.

Links to all of these resources can be found in the Test Centre :

• Oxidation and Reduction Concepts: (tutorial, game, test, drill)
• Oxidation Numbers (States): (tutorial, game, tests, exams)
• Writing Half-equations (simple ions): (tutorial, game, test, drill)
• Writing Half-equations (aqueous solutions): (tutorial, game, test, exam)
• Redox Reaction Concepts: (tutorial, game, test, exams)
• Writing Redox Reaction Equations: (tutorial, game, test, exams)
• Spontaneous and Non-spontaneous Redox Reactions: (tutorial, game, test, exam)
• Displacement Reactions: (tutorial, game, tests, exam)          

Visit www.ausetute.com.au for more information

Olympic Medal Metals

Metallic medals have been awarded to 1^st, 2^nd and 3^rd place Olympic athletes since the 1900 Paris Olympic Games. The medals awarded at the 2012 London Olympic Games are 7mm thick, 85 mm in diameter, and, weigh 400g.
While we happily refer to these olympic medals as gold, silver and bronze, is this chemically accurate?

"Bronze medals" are often made of bronze, an alloy of copper and tin.
At the 2012 London Olympic Games, the bronze medals are made up of a mixture of 97% copper, 2.5% zinc and 0.5% tin. This composition is actually much closer to the composition of brass which is the term used to refer to an alloy of copper and zinc.

"Silver medals" contain at least 92.5% silver. The silver medals awarded in the 2012 Olympic Games were composed of 92.5% silver and 7.5% copper.

"Gold medals" must also contain at least 92.5% silver, but they are plated with at least 6g of gold so they look like "gold" medals. The 2012 Olympic gold medals are made up of 92.5% silver, 6.16% copper and 1.34% gold.

Reference

www.olympic.org/Assets/OSC%20Section/pdf/QR_1E.pdf

Further Reading
Periodic Table
Percentage Composition
Mass-mole Calculations
Moles-Number of Particle Calculations
Density Calculations

Suggested Study Questions

1. Give the chemical symbol for each of the following elements:
   • gold
   • silver
   • copper
   • tin
   • zinc
2. Explain why chemists refer to bronze and brass as alloys.
3. Calculate the mass of each element present in the bronze olympic medals awarded in 2012.
4. Calculate the mole of each element present.
5. For the 2012 Olympic gold medal, calculate the mass of silver present.
6. Calculate the number of silver atoms present in a 2012 olympic gold medal.
7. Calculate the mass of gold present in a 2012 olympic gold medal.
8. Calculate the volume of an olympic medal and use this to calculate the density of an olympic medal.
9. Calculate the surface area of a 2012 Olympic gold medal.
10. Assuming the 2012 gold medal is coated evenly with gold, what thickness is the layer of gold?