10
Stoichiometry I: Calculations
Based on Formulas
A chemical formula tells the numbers and the kinds of atoms that make up a
molecule of a compound. Because each atom is an entity with a characteristic
mass, a formula also provides a means for computing the relative weights of
each kind of atom in a compound. Calculations based on the numbers and
masses of atoms in a compound, or the numbers and masses of molecules
participating in a reaction, are designated \toiihiometric iciknlations. These
weight relationships are important because, although we may think of atoms
and molecules in terms of their interactions as structural units, we often must
deal with them in the lab in terms of their masses—with the analytical balance.
In this chapter, we consider the Stoichiometry of chemical formulas. In following chapters, we look at the stoichiometric relations involved in reactions and in
solutions.
WEIGHTS OF ATOMS AND MOLECULES
The masses of the atoms are the basis for all stoichiometric calculations. Long
before the actual masses of atoms were known, arelathe scale of masses, called
the atomic \\eif>ht scale, was devised. Since 1961, this relative scale has been
based on the assignment of the value 12.00000 to the most common isotope of
carbon. The table on the inside back cover lists approximate values of the
Stoichiometry I: Calculations
Based on Formulas
A chemical formula tells the numbers and the kinds of atoms that make up a
molecule of a compound. Because each atom is an entity with a characteristic
mass, a formula also provides a means for computing the relative weights of
each kind of atom in a compound. Calculations based on the numbers and
masses of atoms in a compound, or the numbers and masses of molecules
participating in a reaction, are designated \toiihiometric iciknlations. These
weight relationships are important because, although we may think of atoms
and molecules in terms of their interactions as structural units, we often must
deal with them in the lab in terms of their masses—with the analytical balance.
In this chapter, we consider the Stoichiometry of chemical formulas. In following chapters, we look at the stoichiometric relations involved in reactions and in
solutions.
WEIGHTS OF ATOMS AND MOLECULES
The masses of the atoms are the basis for all stoichiometric calculations. Long
before the actual masses of atoms were known, arelathe scale of masses, called
the atomic \\eif>ht scale, was devised. Since 1961, this relative scale has been
based on the assignment of the value 12.00000 to the most common isotope of
carbon. The table on the inside back cover lists approximate values of the