Copyright© by Houghton Mifflin Company. All rights reserved. Chapter 15 Solutions.

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Chapter 15Chapter 15

Solutions

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Solutions = homogeneous mixture; a mixture in which the components are uniformly intermingled. All parts are the same; completely mixed.

Solutions can be solids, liquids, or gases.Solid solution = brass (copper = zinc)Solvent = largest amount of substance

presentSolutes = other substances in solutionAqueous solutions = water is solvent

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Figure 15.7: Steps involved in the preparation of a standard aqueous solution.Figure 15.7: Steps involved in the preparation of a standard aqueous solution.

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15.1 15.1 SolubilitySolubility of ionic substances of ionic substances

What is an ionic substance?A substance containing anions (-) and

cations (+) that dissolve in water, separating the ions and thus able to conduct an electric current.

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Figure 15.1: Dissolving of solid sodium chloride.Figure 15.1: Dissolving of solid sodium chloride.

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Solid state ions are packed closely together. Each polar water molecule attaches itself to a sodium ion or a chloride ion.

What does polar mean?One side positive and one side negative. What part of the water molecule attached to

the sodium ions?The oxygen, the negative side.

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Figure 15.2: Polar water molecules interacting with positive and negative ions of a salt.Figure 15.2: Polar water molecules interacting with positive and negative ions of a salt.

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SolubilitySolubility of Polar substances of Polar substances

Polar substances contain a polar bond which makes it able to dissolve in water.

Sugar and ethanol are polar substances.They have an O-H bond where the H can

bond with the water molecule.

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Figure 15.3: The ethanol molecule contains a polar O—H bond.Figure 15.3: The ethanol molecule contains a polar O—H bond.

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Figure 15.3: The polar water molecule interacts strongly with the polar O—H bond in ethanol.Figure 15.3: The polar water molecule interacts strongly with the polar O—H bond in ethanol.

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Figure 15.4: Structure of common table sugar.Figure 15.4: Structure of common table sugar.

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SubstancesSubstances insoluble in water insoluble in water

Petroleum does not dissolve in water.C and H form non polar bonds because C

and H have similar electronegativities.Nonpolar bonds are non-compatible with

the polar bonds in water.**Like substances dissolve.

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Figure 15.5: A molecule typical of those found in petroleum.Figure 15.5: A molecule typical of those found in petroleum.

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Figure 15.6: An oil layer floating on water.Figure 15.6: An oil layer floating on water.

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Which substance is soluble and which is insoluble?Which substance is soluble and which is insoluble?

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15.2 Solution Composition15.2 Solution Composition

The amount of a substance that will dissolve in a solvent is referred to as its solubility. Many factors affect solubility, such as temperature and, in some cases, pressure.– There is a limit as to how much of a given solute will

dissolve at a given temperature.

A saturated solution is one holding as much solute as is allowed at a stated temperature.

Unsaturated = not holding as much as allowed.

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Figure 12.3: Comparison of unsaturated and saturated solutions. Figure 12.3: Comparison of unsaturated and saturated solutions.

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Solubility: Saturated SolutionsSolubility: Saturated Solutions

Sometimes it is possible to obtain a supersaturated solution, that is, one that contains more solute than is allowed at a given temperature.

Supersaturated solutions are unstable.

If a small crystal of the solute is added to a supersaturated solution, the excess immediately crystallizes out.

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Figure 12.4: Crystallization begins.Figure 12.4: Crystallization begins. Photo courtesy of James Scherer. Photo courtesy of James Scherer.

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Amount of substance can vary.Concentrated = a relatively large amount of

soluteDilute = a relatively small amount of solute

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15.3 Factors Affecting Rate of 15.3 Factors Affecting Rate of DissolvingDissolving

1. Surface area – the more surface area exposed, the faster the substance is dissolved

2. Stirring – exposed new surfaces3. Temperature – molecules move faster

thus dissolve faster.

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15.4 Solution Composition: Mass Percent15.4 Solution Composition: Mass Percent

The mass percentage of solute is defined as:

For example, a 3.5% sodium chloride solution contains 3.5 grams NaCl in 100.0 grams of solution.

100% solution of masssolute of mass

solute of percentage Mass

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15.5 Molarity15.5 Molarity

Easier to use volume instead of mass.Concentration = the amount of solute in a

given volume of solution.Concentration = M (Molarity)Standard solution = a solution whose

concentration is accurately known.

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15.5 Molarity15.5 MolarityThe molarity = the number of moles of

solute per volume (liters) of solution.

For example, 0.20 mol of ethylene glycol dissolved in enough water to give 2.0 L of solution has a molarity of

solution of literssolute of moles

)M(Molarity

glycol ethylene M 10.0solution L 0.2 glycol ethylene mol 20.0

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Figure 15.8: Process of making 500 mL of a 1.00 Figure 15.8: Process of making 500 mL of a 1.00 MM acetic acid solution. acetic acid solution.

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Figure 15.9: A bubble in the interior of liquid water surrounded by solute particles and water molecules.Figure 15.9: A bubble in the interior of liquid water surrounded by solute particles and water molecules.

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Figure 15.10: Pure water.Figure 15.10: Pure water.

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Figure 15.10: Solution (contains solute).Figure 15.10: Solution (contains solute).