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Chapter 8 Solutions
Solutions: Solute and Solvent
Solutions
§  Are homogeneous
mixtures of two or
more substances.
§  Consist of a solvent
and one or more
solutes.
8.1
Solutions
1
Nature of Solutes in Solutions
2
Examples of Solutions
Solutes
§  Spread evenly
throughout the solution.
§  Cannot be separated
by filtration.
§  Can be separated by
evaporation.
§  Are not visible, but can
give a color to the
solution.
§  The solute and
solvent in a
solution can be
a solid, liquid,
and/or a gas.
TABLE 8.1
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Learning Check
Solution
Identify the solute in each of the following solutions:
Identify the solute in each of the following solutions:
A. 2 g sugar (1)
A. 2 g sugar (1) and 100 mL water (2)
B. 60.0 mL of ethyl alcohol (1) and 30.0 mL of
methyl alcohol (2)
B. 30.0 mL of methyl alcohol (2)
C. 1.5 g NaCl (2)
C. 55.0 mL water (1) and 1.5 g NaCl (2)
D. 200 mL O2 (1)
D. Air: 200 mL O2 (1) and 800 mL N2 (2)
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Water
Formation of a Solution
Water
§  Is the most
common solvent.
§  Is a polar
molecule.
§  Forms hydrogen
bonds between the
hydrogen atom in
one molecule and
the oxygen atom in
a different water
molecule.
Na+ and Cl- ions
§  On the surface of a
NaCl crystal are
attracted to polar water
molecules.
§  Are hydrated in solution
with many H2O
molecules surrounding
each ion.
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Equations for Solution Formation
Learning Check
When NaCl(s) dissolves in water, the reaction can
be written as
Solid LiCl is added to water. It dissolves because
A. The Li+ ions are attracted to the
1) oxygen atom (δ-) of water.
2) hydrogen atom (δ+) of water.
H 2O
NaCl(s)
solid
Na+(aq) + Cl- (aq)
B. The Cl- ions are attracted to the
1) oxygen atom (δ-) of water.
2) hydrogen atom (δ+) of water.
separation of ions
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Solution
Like Dissolves Like
Solid LiCl is added to water. It dissolves because
A. The Li+ ions are attracted to the
1) oxygen atom (δ-) of water.
Two substances form a solution
§  When there is an attraction between the particles
of the solute and solvent.
§  When a polar solvent, such as water, dissolves
polar solutes, such as sugar, and ionic solutes,
such as NaCl.
B. The Cl- ions are attracted to the
2) hydrogen atom (δ+) of water.
§  When a nonpolar solvent, such as hexane
(C6H14), dissolves nonpolar solutes, such as oil or
grease.
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Water and a Polar Solute
Like Dissolves Like
Solvents
Solutes
Water (polar)
CH2Cl2 (nonpolar)
Ni(NO3)2
(polar)
I2 (nonpolar)
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Learning Check
Solution
Which of the following solutes will dissolve in water?
Why?
Which of the following solutes will dissolve in water?
Why?
1) Na2SO4
Yes, ionic
1) Na2SO4
2) gasoline (nonpolar)
3) I2
4) HCl
2) gasoline
No, nonpolar
3) I2
No, nonpolar
4) HCl
Yes, polar
Most polar and ionic solutes dissolve in water,
because water is a polar solvent.
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Chapter 8 Solutions
Solutes and Ionic Charge
In water,
§  Strong electrolytes produce ions and conduct an
electric current.
§  Weak electrolytes produce a few ions.
§  Nonelectrolytes do not produce ions.
8.2
Electrolytes and Nonelectrolytes
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Strong Electrolytes
Learning Check
Strong electrolytes
§  Dissociate in water producing positive and negative
ions.
§  Conduct an electric current in water.
§  In equations show the formation of ions in aqueous
(aq) solutions.
H 2O
100% ions
NaCl(s)
Na+(aq) + Cl− (aq)
Complete each of the following equations for strong
electrolytes in water:
H 2O
A. CaCl2 (s)
1) CaCl2(s)
2) Ca2+(aq) + Cl2−(aq)
3) Ca2+(aq) + 2Cl−(aq)
H 2O
B. K3PO4 (s)
1) 3K+(aq) + PO43−(aq)
2) K3PO4(s)
3) K3+(aq) + P3−(aq) + O4−(aq)
H 2O
CaBr2(s)
Ca2+(aq) + 2Br− (aq)
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Solution
Weak Electrolytes
Complete each of the following equations for strong
electrolytes in water:
H 2O
A. CaCl2 (s)
3) Ca2+(aq) + 2Cl−(aq)
H 2O
B. K3PO4 (s)
1) 3K+(aq) + PO43−(aq)
A weak electrolyte
§  Dissociates only slightly in water.
§  In water forms a solution of a few ions and mostly
undissociated molecules.
HF(g) +
H2O(l)
NH3(g) + H2O(l)
H3O+(aq) + F- (aq)
NH4+(aq) + OH- (aq)
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Nonelectrolytes
Equivalents
Nonelectrolytes
§  Dissolve as molecules
in water.
§  Do not produce ions in
water.
§  Do not conduct an
electric current.
An equivalent (Eq) is the amount of an electrolyte or an ion
that provides 1 mole of electrical charge (+ or -)
1 mole Na+
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=
1 equivalent
1 mole
Cl−
=
1 equivalent
1 mole
Ca2+
=
2 equivalents
1 mole
Fe3+
=
3 equivalents
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Electrolytes in IV Solutions
Electrolytes in Body Fluids
In replacement solutions for body
fluids, the electrolytes are given in
milliequivalents/L (mEq/L).
Table 8.6
Ringer s Solution
Cations
Anion
Na+ 147 mEq/L
Cl− 155 mEq/L
K+
4 mEq/L
Ca2+
4 mEq/L
155 mEq/L
=
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
155 mEq/L
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Learning Check
Solution
A. In 1 mole of Fe3+, there are
1) 1 Eq
2) 2 Eq
B. In 2.5 mole SO42−, there are
1) 2.5 Eq
2) 5.0 Eq
A. 3) 3 equiv
3) 3 Eq
B. 2) 5.0 Eq
2.5 mole SO42− x 2 Eq
= 5.0 Eq
1 mole SO42−
3) 1.0 Eq
C. 1) 34 mEq/L
C. An IV bottle contains NaCl. If the Na+ is
34 mEq/L, the
1) 34 mEq/L
Cl−
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is
2) 0 mEq/L
3) 68 mEq/L
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Chapter 8
Solutions
Solubility
Solubility is
§  The maximum amount of solute that dissolves in a
specific amount of solvent.
§  Expressed as grams of solute in 100 grams of
solvent, usually water.
g of solute
100 g water
8.3
Solubility
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Unsaturated Solutions
Saturated Solutions
Unsaturated solutions
§  Contain less than the
maximum amount of
solute.
§  Can dissolve more solute.
Saturated solutions
§  Contain the maximum
amount of solute that
can dissolve.
§  Have undissolved
solute at the bottom of
the container.
Dissolved
solute
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Learning Check
Solution
At 40°C, the solubility of KBr is 80 g/100 g H2O.
Identify the following solutions as either
(S) saturated or (U) unsaturated. Explain.
A. 60 g KBr added to 100 g of water at 40°C.
B. 200 g KBr added to 200 g of water at 40°C.
C. 25 g KBr added to 50 g of water at 40°C.
A. U
60 g KBr/100 g water is less than the
solubility of 80 g KBr/100 g water.
B. S
In 100 g of water, 100 g KBr exceeds the
solubility of 80 g KBr water at 40°C.
C. U This is the same as 50 g KBr in 100 g of water,
which is less than the solubility of
80 g KBr/100g water at 40°C.
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Effect of Temperature on
Solubility
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Solubility and Pressure
Henry s Law states
§  The solubility of a
gas in a liquid is
directly related to the
pressure of that gas
above the liquid.
§  At higher pressures,
more gas molecules
dissolve in the liquid.
Solubility
§  Depends on
temperature.
§  Of most solids
increases as
temperature increases.
§  Of gases decreases as
temperature increases.
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Learning Check
Solution
A. Why could a bottle of carbonated drink possibly
burst (explode) when it is left out in the hot sun ?
A. The pressure in a bottle increases as the gas leaves
solution as it becomes less soluble at high
temperatures. As pressure increases, the bottle
could burst.
B. Why do fish die in water that is too warm?
B. Because O2 gas is less soluble in warm water, fish
cannot obtain the amount of O2 required for their
survival.
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Soluble and Insoluble Salts
Solubility Rules
Ionic compounds that
§  Dissolve in water are
soluble salts.
§  Do not dissolve in
water are insoluble
salts.
Soluble salts
§  Typically contain at least one ion from
Groups 1A(1) or
§  NO3−, or C2H3O2− (acetate).
TABLE 8.7
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Using the Solubility Rules
Learning Check
The solubility rules help predict whether a salt is
soluble or insoluble in water.
Use the solubility rules to determine if each salt is
(S) soluble or (I) insoluble.
A. ______ Na2SO4
TABLE 8.8
B. ______ MgCO3
C. ______ PbCl2
D. ______ MgCl2
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Solution
42
Formation of a Solid
A. Na2SO4
(S) Soluble; contains Na+
B. MgCO3
(I) Insoluble; contains carbonates
C. PbCl2
(I) Insoluble; insoluble chloride
D. MgCl2
(S) Soluble; only chlorides of Pb2+, Ag+,
When solutions of salts are mixed,
§  A solid forms if ions of an insoluble salt are present.
and Hg22+ are insoluble
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Equations for Forming Solids
Finding the Insoluble Salt
A molecular equation shows the formulas of the
compounds.
Pb(NO3)(aq) + 2NaCl(aq)
PbCl2(s) + 2NaNO3(aq)
1. Observe the ions in the reactants to see if any new
combination forms an insoluble salt.
Pb2+(aq) + 2NO3−(aq)
PbCl2(s) + 2Na+(aq) + 2NO3−(aq)
+
−
2Na (aq) + 2Cl (aq)
An ionic equation shows the ions of the compounds.
Pb2+(aq) + 2NO3−(aq) + 2Na+(aq) + 2Cl−(aq)
PbCl2(s) + 2Na+(aq) + 2NO3−(aq)
2. Write the insoluble salt as a solid in the products.
Pb2+(aq) + 2Cl−(aq)
PbCl2(s)
A net ionic equation shows only the ions that form a solid.
Pb2+(aq) + 2Cl−(aq)
PbCl2(s)
3. The 2Na+ and 2NO3−(aq) are spectator ions because
they remain unchanged in the reaction.
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Learning Check
Solution
Write the formula of an insoluble salt. If any, and the net
A. BaSO4(s)
Ba2+(aq) + SO42−(aq)
ionic equation for each of the following mixtures:
A. BaCl2(aq) + Na2SO4(aq)
B.
B. AgNO3(aq) + KCl(aq)
C. KNO3(aq) + NaCl(aq)
AgCl
Ag+(aq) + Cl−(aq)
BaSO4(s)
AgCl(s)
C. None; all combinations of ions are soluble salts.
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