Section I. MOLE CONCEPT
In a chemical reaction, atoms and molecules are either combined or separated
during the reaction. In other words, chemical reactions take place at the level of the
atoms and molecules of the reactants.
a. A method that would allow the medical laboratory specialist to know the
relative number of reactant particles involved in a chemical reaction would be useful.
The concept of the mole and molarity provides such a method.
b. One mole of any substance will contain approximately 6.02 X 1023 particles
(Avogadro's number). A mole of a particular substance indicates the number of grams
proportional to the atomic or molecular weight of the substance. This weight is often
referred to as its gram molecular weight.
c. The importance of the mole concept stems from the fact that a mole of any
given element or compound will yield Avogadro's number of particles. If the masses of
samples of two elements or compounds have the same ratio as the ratio of their atomic
weights, the samples contain identical numbers of atoms or molecules.
CALCULATING GRAM MOLECULAR WEIGHT
The gram molecular weight (GMW) is the mass in grams of one mole of substance.
The first step in solving for GMW is to list each element of the compound as represented by
the chemical formula separately. Next, we must take into account the atomic weight of
each individual atom along with the total number of each individual atom or element
present. (See Appendix C for atomic weights and symbols of elements.) Finally, add all
the weights of the atoms making up the formula and express the answer in grams/mole.
a. Example 1. What is the GMW of NaCl?