The Olympics are just months away. Posted on the Official London Olympic Games website are the following facts about the medals of the games.
- The Olympic medals are designed especially for each individual Olympic Games by the host city's organizing committee.
- It was not until the 1904 Olympics in St. Louis that the Games introduced the gold medal as the prize for first place.
- The London 2012 Olympic medals will weigh 375-400 g, be 85 mm in diameter and 7 mm thick.
- The gold medal is made up of 92.5% silver and1.34% gold with the remainder being copper — a required minimum of 6 g of gold.
- The silver medal is made up of 92.5% silver with the remainder copper.
- The bronze medal is made up of 97.0% copper, 2.5% zinc and 0.5% tin.
Plenty of good chemistry questions can be generated from the given data. If you study the data closely you will find a discrepancy, which can be discussed. Here are a few questions to start you off.
What is the volume of the medals?
The information seems to suggest that all the medals (gold, silver and bronze) have the same volume although the photo implies differently. (answer: 40 cm³).
Based on the website information, if the composition of the medal was consistent throughout (do not consider metal plating at this point) what is the maximum density of the Olympic metals? (answer: 10 g/cm³)
Have students determine which medal, based on the percent composition, would have the greatest overall density. Assume the medal alloys are ideal solutions. (answer: gold medal)
If the mass of the gold medal is 400 g and it is 1.34% gold as stated, how much gold is present in the medal? (answer: 5.36 g)
Would this medal meet the minimum standard of having 6 grams of gold? (answer: no)
Have student consider the reasons for this discrepancy. At the time of publication, we are still waiting from the Olympic website and the Royal Mint to clarify some of the information. Perhaps the mass of the metal was just estimated at 400 grams; this could be an opportunity for a class discussion on significant digits. With 1.34% gold composition, have students calculate the minimum mass of the gold medal needed to ensure its mandatory 6 grams of gold (answer: 448 g). If rounded to one significant digit, the answer would be 400 g — although the three digits in 375 g suggest the data are reported to three significant digits.
Although this does not seem to be clear from the above data, other websites (see below) indicate it is the gold-plating on the gold medal that accounts for the 6 grams of gold. The gold and silver medals have the same composition of 92.5% silver alloy aside from this gold plating. This would even lead to the question: given that the density of pure gold is 19.3 g/cm3, what is the thickness of this gold layer? (answer: 0.024 mm)
Websites accessed March 2012