Then, we can break the atom at the carbon-carbon bond, and each half must have a total oxidation state of zero. Carbon may even be present in different oxidation states in the same molecule, as illustrated by this example. D. Measures of Concentration Quantitative analytical chemistry is based on the ability to measure concentration and express it in an unambiguous way. In the environmental sciences, concentrations can be expressed on a mass basis, a molar basis, or an equivalent basis. Since most waters and wastewaters have a density nearly equal to pure water, one liter of these samples may be explicitly equated to one kilogram.
Concentration can also refer to a specific part of a molecule.
For example, a solution of potassium sulfite will contain a certain concentration of K2SO3. Molar concentrations are expressed as the number of moles of a substance present in one liter volume. This corresponds to the quantity of substance in grams which is equal to the atomic weight of the substance, whether it be an atom, a molecule or an ion. It is calculated such that one equivalent of a substance will react with exactly one equivalent of another substance. From equations 2.7, 2.8 and 2.9, the following relationship between molarity and normality can be derived.