Amedeo Avogadro Lab Report

Amedeo Avogadro was an Italian mathematician in the middle 1800’s. He devised a way of measuring the concentration of particles in a sample. Whether the sample is composed of atoms or molecules, he determined that the number of particles having a mass number matching the “atomic weight” was always 6.02 X 1023. In other words, if you had a sample of carbon with a mass of 12.011 grams, then you would have an Avogadro number of atoms. If you had a sample of water with a mass of 18.00 grams, then you would have his number of molecules in that water sample. Avogadro gave us the ability to count particles (concentration) by simply weighing the sample. This made balancing equations and the application of chemistry a predictable science. Avogadro’s number has become the standard in chemistry. When we look at the periodic table, and read the “mass”, we are really getting the mass of six hundred and two, billion-trillion atoms.
In this lab, we take large lima beans and determine their average mass per bean.
As no two lima beans are the exact same size, then they can’t be expected to have the exact same mass. To negate these differences in the beans of our sample, we randomly gather and weigh three groups of beans. Each groups mass is added together. The simple math of dividing the total mass of all of the beans in the three groups by the number of beans which were weighed produces the average mass of one bean. This would be the equivalent of what is now called the molar mass. Now one needs only to weigh a sample of that bean and then divide by this determined average mass, to predict the total number of beans in the sample being investigated. This procedure is repeated for the other three types of beans and a pattern
emerges.
A fifty milliliter beaker was used to create a fixed sample volume. In this experiment, we are trying to determine the number of beans which fit into a 50 ml sample volume. So now, for each of the four bean types tested, a fifty milliliter sample was weighed, and then the number of beans in that sample was predicted. This number is based on the average mass of that bean type. As the data shows, the method is very accurate. As the beans become smaller and lighter, they also have become more numerous. A greater number of smaller beans fits into the fifty milliliter beaker than larger beans. If we were to extend this concept down to the size of an atom, then one can see how particle counts in the trillions could be expected. Avogadro gave us the ability to draw relationships between particle size, particle mass, and particle concentration, contained in a fixed volume of a sample.
To achieve an accurate test of these relationships, a fixed volume for atoms and molecules had to be devised. If we compare the density of a sample, which is the mass of a fixed volume (one cubic centimeter) to the atomic weight (molar mass), then we have our link between Archimedes and Avogadro. How many atoms of aluminum fit into one cubic centimeter of volume? How many atoms of copper fit into that same one cubic centimeter of volume? The math shows that more atoms of copper fit into this common volume associated with density. If copper atoms are smaller, then more will fit into the 1 cc space. Looking at the periodic table, and comparing atomic radii, we see that copper atoms are definitely smaller than aluminum atoms.
In this simple lab exercise with four different bean types, we have linked atomic weight to molar mass. We have related molar mass to particle size and also particle concentration. Thus we have found a relationship between Archimedes and Avogadro across 2200 years of science.