Tuesday November
th
13 ,
2012
Today:
• Chapter 8
• Group Assignment
• Return Exam
Lab This Week:
• Lab 7: Solubility
Next Week:
• No Class
Frequency: CD
Solutions: Solute and Solvent
Solutions
• are homogeneous
mixtures of two or
more substances.
• contain a solute
that is uniformly
dispersed in
another substance
called the solvent.
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
2
Nature of Solutes in Solutions
Solutes
• are spread uniformly
throughout the
solvent.
• are not visible, but
can give a color to
the solution.
• are usually present
in a smaller amount
than the solvent.
Examples of Solutions
The solute and solvent in a solution can be a
solid, liquid, and/or a gas.
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
4
Learning Check
Identify the solute in each of the following
solutions.
1. 2 g sugar and 100 mL water
2. 60.0 mL of ethyl alcohol and 30.0 mL of
methyl alcohol
3. 55.0 mL water and 1.50 g NaCl
4. air: 200 mL O2 and 800 mL N2
Water
• is the most common solvent in nature.
• is a polar molecule.
• forms hydrogen bonds between the partially
positive hydrogen atom in one molecule and the
partially negatively charged oxygen atom in a
different water molecule.
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
6
Formation of a Solution
• To form a solution, the solute and solvent must have
like polarities.
• The energy between the solute and solvent particles
must be strong enough to overcome the initial
attractive forces between the solvent molecules and
solute particles.
Solutions with Ionic and Polar
Solutes
Na+ and Cl– ions
• on the surface of a
NaCl crystal are
attracted to polar
water molecules.
• are hydrated in
solution by many H2O
molecules
surrounding each ion.
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
8
Equations for Solution Formation
When NaCl(s) dissolves in water, the reaction
can be
written as:
Like Dissolves Like
Two substances form a solution when
• there is an attraction between the particles
of the solute and solvent.
• a polar solvent, such as water, dissolves
polar solutes, such as sugar and/or ionic
solutes, such as NaCl.
• a nonpolar solvent, such as hexane (C6H14)
dissolves nonpolar solutes, such as oil or
grease.
Like Dissolves Like
Solvents
Solutes
Water (polar)
CH2Cl2 (nonpolar)
(polar)
Ni(NO3)2
I2 (nonpolar)
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
11
Electrolytes, Nonelectrolytes
In water,
• strong electrolytes separate into ions
making solutions that conduct electricity.
• weak electrolytes produce a few ions.
• nonelectrolytes produce molecules, not
ions.
Strong Electrolytes
Solutes that are strong electrolytes
• dissociate 100% or break up into positive and
negative ions in water.
• form aqueous solutions (aq) when dissolved
in water that will conduct an electrical
current.
H2 O
100% ions
NaCl(s)
Na+(aq) + Cl(aq)
H2 O
CaBr2(s)
Ca2+(aq) + 2Br(aq)
Weak Electrolytes
Solutes that are weak electrolytes
• dissolve in water mostly as molecules.
• dissolve in water forming a few ions.
• produce solutions that conduct electricity
weakly.
Nonelectrolytes
Solutes that are
nonelectrolytes
• dissolve as molecules in
water.
• do not produce ions in
water.
• form solutions that do not
conduct an electrical
current.
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
15
Classification of Solutes in Aqueous
Solutions
Equivalents
An equivalent (Eq) is the amount of that ion equal
to 1 mole of positive or negative electrical charge
(+ or –). For example:
• 1 mole of Na+ ions and 1 mole of Cl− ions are each
1 equivalent or 1000 milliequivalents (mEq)
because they each contain 1 mole of charge, and
• ions with a charge of 2+ or 2−, contain 2
equivalents for each mole.
1 mole Na+ = 1 Eq
1 mole Ca2+ = 2 Eq
1 mole S2− = 2 Eq
Equivalents of Electrolytes
Electrolytes in Body Fluids
Electrolytes play an important role in maintaining the
proper function of the cells and organs in the body.
• Sodium ions regulate water content and carry electrical
impulses through the nervous system.
• Potassium ions are involved in the transmission of electrical
impulses and help maintain a regular heartbeat.
• Bicarbonate ions help maintain blood pH.
Electrolytes in Blood Plasma
Solubility
Solubility is the amount of solute that dissolves in a
specific amount of solvent at a given temperature and is
• affected by the type of solvent and temperature
• expressed as grams of solute per 100 grams of solvent
(usually water):
Unsaturated Solutions
Unsaturated solutions
contain less than the
maximum amount of
solute.
Dissolved
solute
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
22
Saturated Solutions
Saturated solutions
contain the maximum
amount of solute that
can dissolve in the
solvent.
The rate at which the
solute dissolves equals
the rate at which the
solute forms.
© 2013 Pearson Education, Inc.
Dissolved
solute
Undissolved
solute
Chapter 8, Section 1
23
Learning Check
At 40 C, the solubility of KBr is 80 g/100 g of
H2O.
Identify the following solutions as either
saturated (S)
or unsaturated (U). Explain.
1. 200 g KBr is added to 200 g of water at 40 C.
2. 25 g KBr is added to 50 g of water at 40 C.
Solution
At 40 C, the solubility of KBr is 80 g/100 g of H2O.
Identify the following solutions as either saturated (S)
or unsaturated (U). Explain.
1. S 200 g KBr is added to 200 g of water at 40 C.
This is the same as 100 g of KBr in 100 g of
water, which is more than the solubility of 80 g
of KBr/100 g of water at 40 C.
2. U 25 g KBr is added to 50 g of water at 40 C. This
is the same as 50 g of KBr in 100 g of water,
which is less than the solubility of 80 g of KBr/
100 g of water at 40 C.
Effect of Temperature on Solubility
Solubility depends on
temperature. The
solubility
• of most solids
increases as
temperature increases
• of gases decreases as
temperature increases
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
26
Solubility and Pressure
Henry’s law states that
• 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
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
27
Learning Check
1. Why could a bottle of carbonated drink
possibly burst (explode) when it is left
out in the hot sun?
2. Why do fish die in water that is too
warm?
Solution
1. Why could a bottle of carbonated drink
possibly burst (explode) when it is left out in
the hot sun?
Gases become less soluble at high
temperatures and leave the solution. As
pressure inside the container increases, the
bottle could burst.
2. Why do fish die in water that is too warm?
Because O2 gas is less soluble in warm water,
fish cannot obtain enough O2 to survive.
Soluble and Insoluble Salts
Ionic compounds that
• dissolve in water are soluble salts
• do not dissolve in water are insoluble salts
Mixing certain aqueous solutions produces insoluble salts.
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
30
Solubility Rules
• Soluble salts
typically contain at
least one ion from
Groups 1A(1),
NO3−, NH4+ or
C2H3O2− (acetate).
• Most other
combinations are
insoluble.
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
31
Using the Solubility Rules
© 2013 Pearson Education, Inc.
Chapter 8, Section 1
32
Learning Check
Use the solubility rules to determine if
each salt is
soluble or insoluble. Explain.
1.
2.
3.
4.
Na2SO4
MgCO3
PbCl2
MgCl2
Solution
Use the solubility rules to determine if each
salt is
soluble or insoluble. Explain.
1.
2.
3.
4.
Na2SO4
MgCO3
PbCl2
MgCl2
soluble; contains Na+
insoluble; contains carbonates
insoluble; insoluble chloride
soluble; only chlorides of Pb2+, Ag+,
and Hg22+ are insoluble
Formation of a Solid
We can use solubility rules to predict whether a solid,
called a precipitate, forms when two solutions of ionic
compounds are mixed.
Example:
AgNO3(aq) + NaCl(aq)
AgCl(s) + NaNO3(aq)
Equations for Forming Solids
A full equation shows the formulas of the
compounds.
An ionic equation shows the ions of the
compounds.
A net ionic equation shows only the ions that form
a solid.
Guide to Writing New Ionic
Equations for an Insoluble Salt
Learning Check
When solutions of Na2CO3 and Ba(NO3)2 are
mixed, a white solid forms. Write the ionic
and net ionic equations for the reaction.
Solution
When solutions of Na2CO3 and Ba(NO3)2 are mixed, a
white solid forms. Write the ionic and net ionic
quations for the reaction.
Step 1 Write the ions of the reactants.
Ba2+(aq) + 2NO3−(aq)
2Na+(aq) +
CO32−(aq)
Solution
When solutions of Na2CO3 and Ba(NO3)2 are mixed, a
white solid forms. Write the ionic and net ionic
equations for the reaction.
Step 2 Write the combinations of ions and
determine if any are insoluble.
Mixture
Product
Soluble
2Na+(aq) + 2NO3−(aq)
2NaNO3 (aq)
yes
Ba2+(aq) + CO32-(aq)
BaCO3(s)
no
Solution
When solutions of Na2CO3 and Ba(NO3)2 are mixed, a
white solid forms. Write the ionic and net ionic equations
for the reaction.
Step 3 Write the ionic equation, including any
insoluble salt as a solid.
Step 4 Write the net ionic equation deleting spectator
ions.