This lesson introduces the mole concept in terms of counting particles, and proceeds to the determination of empirical formulas from mass percent. It sets up subsequent lessons on combustion analysis and calculations involving chemical reactions.
Chapter 1 starts with a series of three quizzes to extend the significance of the numbers in a formula. This is done in simple integers, then in units of dozens and finally in units of moles. For example, the formula (NH4)3PO4 tells you that there are three ammonium groups for every four oxygen atoms, etc. This also means three phosphorus atoms for every nine nitrogen atoms, or six dozen ammonium groups for every two dozen phosphates, or 24 moles of hydrogen atoms for every eight moles of oxygen atoms, and so on. Avogadro's number is introduced, and the next quiz requires the student to express the number of atoms or groups in a sample whose formula is known, given the number of moles of another atom or group.
Chapter 2 deals with the molar mass. "Atomic weights" and "molecular weights" are shown to be specialized molar masses.
Chapter 3 has a simple quiz on using the molar mass to convert between number (moles) and mass (grams). Next, the mass percent is defined, and there is an exercise in which one learns how to get mass percent from the formula, using the atomic weight table.
The chapter then concludes with the determination of empirical formula from the mass analysis. The student is coached through this determination, with feedback and helpful hints at all points from an expert system.
The mass percentages are presented, as shown in the figure.
The student then answers a series of questions, which lead to the mole proportions and thus the formula.
At each point, once it is evident that the student has caught on, the computer will complete that part. For example, if the student chooses to work with 100 grams, the computer immediately shows the masses of all the elements.
Once a student gets a mole amount correct, the computer calculates the remaining ones, and so on.
The lesson ends with a quiz in which the mass percents are
given and the student must deduce the empirical formula. There is a large database of
compounds, and no limit on
the number one can try. A score results, which is recorded in a dataset.
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Updated July 18, 2000