Chap 4 notes - What Is a Solution? A solution is a...

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What Is a Solution? A solution is a homogeneous mixture of one or more solutes dissolved in a solvent. solvent : the substance in which a solute dissolves to produce a homogeneous mixture solute : the substance that dissolves in a solvent to produce a homogeneous mixture Note that the solvent is the substance that is present in the greatest amount. Many different kinds of solutions exist. For example, a solute can be a gas, a liquid or a solid. Solvents can also be gases, liquids or solids. The following figures show the microscopic behavior of several different kinds of solutions. Note that in each case, the solute particles are uniformly distributed among the solvent particles. Microscopic view of Br 2 gas (solute) dissolved in Ar gas (solvent). Microscopic view of Ar gas (solute) dissolved in liquid H 2 O (solvent). Microscopic view of Br 2 liquid (solute) dissolved in liquid H 2 O (solvent). Microscopic view of solid NaCl (solute) dissolved in liquid H 2 O (solvent). Note that the ionic solid, NaCl, produces Na + ions (blue) and Cl - ions (green) when dissolved in water. Microscopic view of solid Kr (solute, blue ) dissolved in solid Xe (solvent, red ). Expressing Concentration
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The concentration of a solution is a macroscopic property, represents the amount of solute dissolved in a unit amount of solvent or of solution, and can be expressed in a variety of ways (qualitatively and quantitatively). Qualitative Expressions of Concentration A solution can be qualitatively described as dilute : a solution that contains a small proportion of solute relative to solvent, or concentrated : a solution that contains a large proportion of solute relative to solvent. Microscopic view of a dilute solution of liquid Br 2 dissolved in liquid water. Microscopic view of a concentrated solution of liquid Br 2 dissolved in liquid water. Semi-Quantitative Expressions of Concentration A solution can be semi-quantitatively described as unsaturated : a solution in which more solute will dissolve, or saturated : a solution in which no more solute will dissolve. The solubility of a solute is the amount of solute that will dissolve in a given amount of solvent to produce a saturated solution. For example, at 0 o C, we can dissolve a maximum of 35.7 g of solid NaCl in 100 mL of water (a saturated solution). Any additional solid NaCl that we add to the saturated solution simply falls to the bottom of the container and does not dissolve. Quantitative Expressions of Concentration There are a number of ways to express the relative amounts of solute and solvent in a solution. Which one we choose to use often depends on convenience. For example, it is sometimes easier to measure the volume of a solution rather than the mass of the solution. Note that some expressions for concentration are temperature-dependent (i.e., the concentration
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This note was uploaded on 02/05/2012 for the course CHEM 115 taught by Professor L during the Fall '02 term at Purdue University-West Lafayette.

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Chap 4 notes - What Is a Solution? A solution is a...

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