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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).