Friday, April 15, 2005

What is Fool's Gold?

You've probably heard of "fool's gold" before, but what exactly is it and how does it differ from real gold? The technical name for fool's gold is pyrite. Like real gold, it is brass-colored, hard, and shiny. However, it is not made out of gold, which is why it's not nearly as valuable.

Pieces of pyrite have jagged edges and can sometimes form cubes. Sometimes pyrite also has a grain (sets of lines, just like in wood). Pyrite can be found right here in Pennsylvania, but it is also located in other states, as well as in Mexico and Europe.

True gold is an element. Elements are the smallest building blocks of everything in the universe. They are made of positively-charged particles (protons), negatively-charged particles (electrons), and neutral (non-charged) particles called neutrons. The only difference between different elements is how many of each type of particle they contain.

Besides gold, some other elements that you may have heard of are: silver, iron, mercury, and oxygen. As you can see from that list, elements can be solids, liquids, or gases.

The smallest piece or unit of an element is called an atom. Atoms can combine with each other to form molecules. Some molecules (like oxygen) are just made up of one element. The oxygen that we breathe is written as O2, since there are 2 atoms of oxygen in each molecule, and the symbol for oxygen is O. In other words, oxygen atoms are floating around in the air in pairs.

In contrast to O2, most molecules are made up of two or more different elements. For example, you may have heard water referred to as "H2O." This means that each molecule of water contains 2 hydrogen (H) atoms and 1 oxygen (O) atom.

You might be wondering why we don't write water as H2O1. It is just a scientific custom to not write 1 when there is only 1 atom of a given element in the molecule. By the same token, you can think of your hand as Finger5Palm since each hand is made up of 5 fingers and one palm.

Make sense? Now let's apply what we just learned and figure out the symbol for fool's gold! In contrast to real gold, pyrite is made of the two elements iron and sulfur. The symbol for iron is "Fe" and the symbol for sulfur is "S." Each molecule of pyrite is made up of 1 atom of iron (Fe) and 2 atoms of sulfur (S). So, pyrite is written as FeS2. In case you were wondering, the symbol for real gold is Au.

Little Lion Experiment:

When pyrite mixes with acid rain, it dissociates (comes apart) so now the iron and sulfur are separated from each other and are no longer grouped into molecules of pyrite. When molecules dissociate, you can't see them anymore since they are broken up into such tiny pieces. So, the solutions (mixture) is clear.

When this solution mixes with groundwater (which isn't acidic), the iron can't remain in the solution and so it sinks to the bottom. But since it is exposed to water and air, it rusts. So, you are left with a rust-colored gel from the wet rusted iron. You may have seen this on rocks at the bottom of streams.

Most people don't have pyrite at home, so we're going to use antacids, which will behave the same way as pyrite does in this experiment. Ask your parents for an antacid tablet (like TUMS or Maalox). This experiment will be easier to see if the tablet is colored instead of white. If you don't have antacids, then ask for a calcium vitamin.

Break off a pea-sized piece, place it between two paper towels, then use a spoon to grind the tablet into a very fine powder. Put the powder into a cup. Add a teaspoon of water (this is like groundwater). Mix, and notice how the dust doesn't dissolve (you can still see it). To mimic acid rain, add a teaspoon of lemon juice (this is an acid). Mix, and see if some of the dust dissolves. The solution should become more transparent (see-through) since there is less powder floating on top.