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The Learning Goal for this assignment is:<br />
The students will learn what properties are used to describe the nature of solutions and how to quantify<br />
the concentration of a solution.<br />
Defining Concentration<br />
Measures of Concentration<br />
Concentration is defined as the amount of dissolved solute in a given amount of solvent or<br />
solution. There are several terms that describe concentration. Some of these terms are relative;<br />
that is, they can be used only to compare the concentration of one solution to another. Dilute and<br />
concentrated are two such terms. A dilute solution contains less dissolved solute than a<br />
concentrated solution (in equal volumes of solution).<br />
The terms saturated, unsaturated, and supersaturated are terms that describe concentration more<br />
precisely.<br />
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Saturated: The maximum amount of solute is dissolved in a given amount of solvent at a<br />
particular temperature. Such solutions are stable.<br />
Unsaturated: Less than the maximum amount of solute is dissolved in a given amount of<br />
solvent at a particular temperature. Such solutions are stable.<br />
Supersaturated: More than the maximum amount of solute is dissolved in a given amount of<br />
solvent at a particular temperature. Such solutions are unstable.<br />
Look at the solubility curve shown below:<br />
Page 128<br />
The solubility of NaNO3 is 86.0 g/100 mL H2O (at 20 °C). If you<br />
prepare a solution of 50.0 g NaNO3 dissolved in 100 mL H2O, an unsaturated solution results<br />
(Point A on the graph).<br />
continue adding NaNO to the solution until 86.0 g are dissolved, a saturated solution results<br />
(Point B).<br />
heat the solution to 50 °C, 113 grams NaNO3 can be dissolved (Point C). When the solution<br />
cools back down to 20 °C, it will be supersaturated (Point D).<br />
Quantifying Concentration<br />
To describe the concentration of a solution even more precisely, various measures of concentration<br />
can be used. Some of the ways concentration can be quantified include calculating the<br />
Mass of solute per solution mass (expressed as a percent or parts per million)<br />
Moles of solute per kilogram solvent (molality)<br />
Mass of solute per liter of solution (grams/liter)<br />
Moles of solute per liter of solution (molarity)