Calculating the Amount of a Substance in Moles or Millimoles

The two examples that follow illustrate how the number of moles or millimoles of a species can be determined from its mass in grams or from the mass of a chemically related species.

Some students and instructors find it easier to write out the solution to a problem so that units in the denominator of each succeeding term eliminate the units in the numerator of the preceding one until the units of the answer are obtained. This method has been referred to as the factor-label method, dimensional analysis, or the picket fence method. For instance, in Example below, the units of the answer are g Na⁺, and the units given are g Na₂SO₄. Thus, we can write