Solve et Coagula: Exploring Alchemy and Sustainability with Gold

Instructor notes are provided in the resource and summarized here:

This experiment can be performed with a single item of jewelry that contains gold (e.g. 14k ring or necklace) and other samples made of base metals (iron, copper, etc.).

It may also be reformatted to focus on silver versus sterling silver, which is easy to acquire at a flea market.

Before performing the acid test, students are shown the precipitation of potassium iodide and lead nitrate to foster a discussion of how lead might be turned into gold and introduce the philosopher’s stone.

Aqua regia is a mixture of strong acids and should be carefully handled. In the case where students do not yet have experience handling acids, they may handle the metals, and the instructors may add the acid to the slate.

Acid test kits are available online, and a single kit may be used with roughly 20 students at a time in small groups. Note that the acids can degrade over time, and a new kit or freshly prepared acid solutions should always be used for best results. Many of these kits contain not only different acid concentrations for different caratages of gold, but also acids for testing silver and platinum.

Always begin by using the lowest concentration of acid (e.g. 10k solution) and then increase the concentration and work up to higher percentages of gold (e.g. 22k).

Note that most commercial samples of jewelry are not above 18k, so a quick test is to perform the 10k and 22k, to first determine if it is gold, and then if it is a high percentage or not.

Neutralize the acids on the black slate by sprinkling baking soda until the mixture no longer reacts. The resultant water and salt may be safely rinsed down the drain.

As the metal is drawn onto the black slate by scratching it, students are invited to test jewelry of their own, but must note that it will scuff and may damage the item.

Be careful when performing this experiment on items of jewelry that may have sentimental value. Participants may be sad to know their jewelry is not real (or as real) as they previously thought.