# 7.18: Concentrations: Qualitative Comparisons

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The previous six sections of this chapter have presented and applied the equations that are used to calculate the mass percent, the volume percent, the mass/volume percent, and the molarity of a solution. Each of these concentrations *quantitatively *ratios the amount of solute that is contained in a solution to the amount of solution that is present, overall. This generic definition of concentration is represented in the equation that is shown below.

\(\text{Concentration (C)}\) = \( \dfrac{ \rm{Amount \; of \; Solute}}{\rm{Amount \; of \; Solution}}\)

When the concentrations of multiple solutions are compared to one another, each homogeneous mixture can be *qualitatively described* as being "concentrated" or "dilute," *relative to the other solution.* Because the meanings of these terms are defined based on the *relative comparisons* of two or more solutions, neither of these words is quantitative on its own. If a large amount of solute is dissolved in a particular amount of solvent, the resultant solution can likely be described as **concentrated**. In order to be classified as **dilute**, a solution must contain *less solute in the same amount of solvent* or *the same amount of solute in a larger amount of solvent*, relative to the solution to which it is being compared.

The impact of these changes on the concentration of a solution can be evaluated using the generic equation that is shown above. If the quantity of solvent and, therefore, the denominator in this equation, is unchanged, *reducing *the amount of *solute *that is present *lessens *the value of the *numerator *in this proportion, and, consequently, the concentration of the solution *decreases*. When the amount of solute and, therefore, the numerator in this equation, remains constant, *increasing *the quantity of *solution *that is present *raises *the value in the *denominator *of this ratio, which, in turn, *decreases* the concentration of the solution. Therefore, compared to a more concentrated solution, a solution that is classified as "dilute" must have a *smaller* relative concentration. For example, a 5.2 *M* solution is *more concentrated* than a 1.7 *M* solution, but is *more dilute* than a 6.4 *M* solution.

Note that a concentrated solution should *not *be described as "strong" or assumed to be saturated, and a dilute solution should *not* be equated to being "weak." As discussed previously, the words "strong" and "weak" refer to the extent to which a solute dissociates, or separates, into ions during the solvation process. Since the concentration of a solution is solely dependent on the *amounts* of chemicals that are present, the *type* of solute, which dictates the extent to which that chemical dissociates, does not impact whether a solution is concentrated or dilute. Finally, a saturated solution must, by definition, contain * exactly* the maximum amount of solute that can be dissolved in a specified amount of solvent. Therefore, while a

*saturated*solution is most likely

*concentrated*, a concentrated solution is

*not necessarily*saturated.