Properties of Solutions
 Solvent
This is the liquid that is doing the dissolving
 Solute
 This is what is being dissolved
 Form a homogenous mixture

Saturated vs. Unsaturated Solutions
Solubility
Two liquids that dissolve in each
other are said to be miscible
Immiscible liquids are insoluble in
each other
Think of some examples!
Immiscible vs. Miscible Solutions
Factors Affecting Solubility
Solubility increases with the
increase in temperature (Easier to
dissolve something when the
temperature is increased)
Few exceptions that occur in the
reverse
Concentrations of Solutions
 Molarity is the concentration of moles per
liters
 Molarity (M) = moles of solute / liters of
solution
 Dilute solution contains a low
concentration of solute
 Concentrated solution contains a high
concentration of solute
Practice Problems:
 Calculate the molarity of a solution which contains
0.40 mol of C6H12O6 dissolved in 1.6 L of a solution.
 What is the molarity of a solution containing 325 g of
NaCl dissolved in 750. mL of solution?(1000 ml = 1L)
Making Dilutions
 Formula for making
a dilution
C1 V1 = C2 V2
(Volume must be in units of L)
 “Stock solution” is
the same as the
original solution.
Example
 A stock solution of HCl has a concentration of 12M.
How much of the stock solution would be required to
make 325 mL of a 6M solution?
Stoichiometry overview

Recall that in stoichiometry the mole ratio provides a
necessary conversion factor:
molar mass of x
molar mass of y
grams (x)  moles (x)  moles (y)  grams (y)
mole ratio from balanced equation
We can do something similar with solutions:
mol/L of x
mol/L of y
volume (x)  moles (x)  moles (y)  volume (y)
mole ratio from balanced equation
Practice Problems
1. If I combined 15.0 grams of calcium hydroxide with 0.075
L of 0.500 M HCl, how many grams of calcium chloride would
be formed?
2. If 257.8 ml of a 0.0468 M solution of lead(II) acetate is
added to 156.00 mL of a 0.095 M solution of sodium sulfide,
what mass of solid lead sulfide will be formed?
What Happens When a Solute Dissolves?
 there are attractive forces between the solute particles
holding them together; likewise for the solvent
 Upon mixing the solute with the solvent, there are
attractive forces between the solute particles and the
solvent molecules
 if the attractions between solute and solvent are strong
enough, the solute will dissolve
14
Table Salt Dissolving in Water
Each ion is attracted to the
surrounding water
molecules and pulled off
and away from the crystal
When it enters the
solution, the ion is
surrounded by water
molecules, insulating it
from other ions
The result is a solution with
free moving charged
particles able to conduct
electricity
Tro, Chemistry: A Molecular
Approach
15
Electrolytes and Nonelectrolytes
 materials that dissolve in
water to form a solution that
will conduct electricity are
called electrolytes
 materials that dissolve in
water to form a solution that
will not conduct electricity
are called nonelectrolytes
Tro, Chemistry: A Molecular
Approach
16
Molecular View of
Electrolytes and Nonelectrolytes
 in order to conduct electricity, a material must have
charged particles that are able to flow
 electrolyte solutions all contain ions dissolved in the
water
 ionic compounds are electrolytes because they all
dissociate into their ions when they dissolve
 nonelectrolyte solutions contain whole molecules
dissolved in the water
 generally, molecular compounds do not ionize when they
dissolve in water

the notable exception being molecular acids
Tro, Chemistry: A Molecular
Approach
17
Salt vs. Sugar Dissolved in Water
ionic compounds dissociate into
ions when they dissolve
Tro, Chemistry: A Molecular
Approach
18
molecular compounds do not
dissociate when they dissolve
Acids
 acids are molecular compounds that ionize when they
dissolve in water
 the molecules are pulled apart by their attraction for the water
 when acids ionize, they form H+ cations and anions
 the percentage of molecules that ionize varies from one
acid to another
 acids that ionize virtually 100% are called strong acids
HCl(aq)  H+(aq) + Cl-(aq)
 acids that only ionize a small percentage are called weak
acids
HF(aq)  H+(aq) + F-(aq)
Tro, Chemistry: A Molecular
Approach
19
Strong
and
Weak
Electrolytes
 strong electrolytes are materials that dissolve
completely as ions
 ionic compounds and strong acids
 their solutions conduct electricity well
 weak electrolytes are materials that dissolve
mostly as molecules, but partially as ions
 weak acids
 their solutions conduct electricity, but not well
 when compounds containing a polyatomic ion
dissolve, the polyatomic ion stays together
Na2SO4(aq)  2 Na+(aq) + SO42-(aq)
HC2H3O2(aq)  H+(aq) + C2H3O2-(aq)
Tro, Chemistry: A Molecular
Approach
20
Classes of Dissolved Materials
Tro, Chemistry: A Molecular
Approach
21
Acid-Base Reactions
 also called neutralization reactions because
the acid and base neutralize each other’s
properties
2 HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2(aq) + 2 H2O(l)
 the net ionic equation for an acid-base reaction
is
H+(aq) + OH(aq)  H2O(l)
 as long as the salt that forms is soluble in
water
Tro, Chemistry: A Molecular
Approach
22
Acids
and
Bases
in
Solution
 acids ionize in water to form H ions
+
 more precisely, the H from the acid molecule is donated to a
water molecule to form hydronium ion, H3O+

most chemists use H+ and H3O+ interchangeably
 bases dissociate in water to form OH ions
 bases, like NH3, that do not contain OH ions, produce OH
by pulling H off water molecules
 in the reaction of an acid with a base, the H+ from the
acid combines with the OH from the base to make
water
 the cation from the base combines with the anion
from the acid to make the salt
acid + base salt + water
Tro, Chemistry: A Molecular
Approach
23
Practice
 Write the balanced molecular and net ionic
equations for the reaction between:
 1. Hydrobromic Acid and Potassium Hydroxide
 2. Nitric Acid and Calcium Hydroxide
 ****Hint: Remember what an acid-base reaction
always produces!
Electrolytes
Strong Acids and
Strong Bases= Strong
Electrolytes
Weak Acids and
Weak Bases = Weak
Electrolytes
Red-ox Reactions
 other kinds of reactions involve
transferring electrons from one atom to
another – these are called oxidationreduction reactions
 also known as redox reactions
 many involve the reaction of a
substance with O2(g)
4 Fe(s) + 3 O2(g)  2 Fe2O3(s)
Tro, Chemistry: A Molecular
Approach
26
Oxidation and Reduction
atoms that lose electrons are
being oxidized, atoms that
gain electrons are being
reduced
2 Na(s) + Cl2(g) → 2 Na+Cl–(s)
2Na → 2Na+ + 2e– oxidation
Cl2 + 2 e– → 2 Cl– reduction
Tro, Chemistry: A Molecular
Approach
27
Leo
Ger
Electron Bookkeeping
 for reactions that are not metal + nonmetal, or
do not involve O2, we need a method for
determining how the electrons are transferred
 chemists assign a number to each element in a
reaction called an oxidation state that allows
them to determine the electron flow in the
reaction
 even though they look like them, oxidation states
are not ion charges!


oxidation states are imaginary charges assigned based on
a set of rules
ion charges are real, measurable charges
Tro, Chemistry: A Molecular
Approach
28
Rules for Assigning Oxidation States

1.
rules are in order of priority
free elements have an oxidation state = 0

Na = 0 and Cl2 = 0 in 2 Na(s) + Cl2(g)
monatomic ions have an oxidation state equal to their
charge
2.

Na = +1 and Cl = -1 in NaCl
(a) the sum of the oxidation states of all the atoms in a
compound is 0
3.

Na = +1 and Cl = -1 in NaCl, (+1) + (-1) = 0
Tro, Chemistry: A Molecular
Approach
29
Rules for Assigning Oxidation States
(b) the sum of the oxidation states of all the atoms
in a polyatomic ion equals the charge on the ion
3.

N = +5 and O = -2 in NO3–, (+5) + 3(-2) = -1
(a) Group I metals have an oxidation state of +1 in
all their compounds
4.

Na = +1 in NaCl
(b) Group II metals have an oxidation state of +2
in all their compounds
4.

Mg = +2 in MgCl2
Tro, Chemistry: A Molecular
Approach
30
Rules for Assigning Oxidation States
in their compounds, nonmetals have oxidation states
according to the table below
5.

nonmetals higher on the table take priority
Nonmetal
Oxidation State
Example
F
-1
CF4
H
+1
CH4
O
-2
CO2
Group 7A
-1
CCl4
Group 6A
-2
CS2
Group 5A
-3
NH3
Tro, Chemistry: A Molecular
Approach
31
Practice – Assign an Oxidation State to
Each Element in the following
 Br2
 K+
 LiF
 CO2
 SO42-
 Na2O2
Tro, Chemistry: A Molecular
Approach
32
Practice – Assign an Oxidation State to
Each Element in the following
 Br2
Br = 0, (Rule 1)
 K+
K = +1, (Rule 2)
 LiF
Li = +1, (Rule 4a) & F = -1, (Rule 5)
 CO2 O = -2, (Rule 5) & C = +4, (Rule 3a)
 SO42-
O = -2, (Rule 5) & S = +6, (Rule 3b)
 Na2O2
Na = +1, (Rule 4a) & O = -1, (Rule 3a)
Tro, Chemistry: A Molecular
Approach
33
Oxidation and Reduction
Another Definition
 oxidation occurs when an atom’s oxidation state
increases during a reaction
 reduction occurs when an atom’s oxidation state
decreases during a reaction
CH4 + 2 O2 → CO2 + 2 H2O
-4 +1
0
+4 –2
+1 -2
oxidation
reduction
Tro, Chemistry: A Molecular
Approach
34
Oxidation–Reduction
 oxidation and reduction must occur simultaneously
 if an atom loses electrons another atom must take them
 the reactant that reduces an element in another
reactant is called the reducing agent
 the reducing agent contains the element that is oxidized
 the reactant that oxidizes an element in another
reactant is called the oxidizing agent
 the oxidizing agent contains the element that is reduced
2 Na(s) + Cl2(g) → 2 Na+Cl–(s)
Na is oxidized, Cl is reduced
Na is the reducing agent, Cl2 is the oxidizing agent
Tro, Chemistry: A Molecular
Approach
35
Identify the Oxidizing and Reducing Agents in
Each of the Following
3 H2S + 2 NO3– + 2 H+ 3 S + 2 NO + 4 H2O
MnO2 + 4 HBr MnBr2 + Br2 + 2 H2O
Tro, Chemistry: A Molecular
Approach
36