Unit 5 - Counting
Particles Too Small to See
How many gum balls are in the machine? Counting them would certainly be a chore. However, it would pale in comparison to counting atoms and molecules. How did scientists figure out how many particles are in a give sample of a substance if these particles are invisible?
From Avogadro's Hypothesis we are able to count molecules by weighing macroscopic samples.
For gases at the same temperature and pressure we can deduce the following:
1. From combining volumes we can determine the ratio in which molecules react.
2. From masses of these gases we can determine the relative mass of individual molecules.
From these results it is possible to determine the molar masses of the elements; using these masses and formulas of compounds, one can determine molar masses of compounds. The mole was defined in terms of a readily weighable “lump” of a substance. These tools allow one to relate “how much stuff” to “how many particles".
Dr. Michael M. Krop High School
Unit 5 Materials
Worksheet 1 - Moles to grams; grams to moles
Worksheet 2 - Empirical and molecular formulas
Worksheet 3 - More practice on empirical formula nomenclature