Chapter 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
present
 Solutes = other substances in solution
 Aqueous solutions = water is solvent
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Figure 15.7: Steps involved in the preparation of a standard aqueous solution.
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15.1 Solubility 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.
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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.
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Solubility 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.
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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.
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Substances 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.
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Figure 15.6: An oil layer floating on water.
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Which substance is soluble and which is insoluble?
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15.2 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.
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Solubility: 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.
Photo courtesy of James Scherer.
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
Amount of substance can vary.
 Concentrated = a relatively large amount of
solute
 Dilute = a relatively small amount of solute
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15.3 Factors Affecting Rate of
Dissolving
1. Surface area – the more surface area
exposed, the faster the substance is
dissolved
 2. Stirring – exposed new surfaces
 3. Temperature – molecules move faster
thus dissolve faster.

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15.4 Solution Composition: Mass Percent

The mass percentage of solute is defined as:
mass of solute
Mass percentage of solute 
 100%
mass of solution
For example, a 3.5% sodium chloride solution
contains 3.5 grams NaCl in 100.0 grams of
solution.
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15.5 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 Molarity

The molarity = the number of moles of
solute per volume (liters) of solution.
moles of solute
Molarity(M ) 
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
0.20 mol ethylene glycol
2.0 L solution
 0.10 M ethylene glycol
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Figure 15.8: Process of making 500 mL of a 1.00 M 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.
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Figure 15.10: Pure water.
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Figure 15.10: Solution (contains solute).
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