Fri | Sep 7, 2007
 Chapter 4: Types of Chemical Reactions
– Precipitation Reactions (Sections 4.5 - 4.8)
– Acid-Base Reactions (Section 4.9 )
– Oxidation-Reduction Reactions (Section 4.10 - 4.12)
 Exam #1 - Next Friday (Sep 14)
Attendance is mandatory on Sep 14!
Week 3
CHEM 1310 - Sections L and M
1
What is a Precipitation Rxn?
A type of reaction in which a solute exceeds its
own solubility in the given solution
Week 3
CHEM 1310 - Sections L and M
2
1
Precipitation Conditions
Under what types of conditions will precipitation
occur?
 Addition of Excess Solute
 Removal of Solvent
 Change of Solvent
 Change of Temperature
Week 3
CHEM 1310 - Sections L and M
3
Questions re: Precipitation Rxns
How could one predict
what product would
precipitate in a given
precipitation reaction?
How would one write a
chemical equation to
represent a precipitation
reaction
Week 3
CHEM 1310 - Sections L and M
4
2
Predicting ID of Precipitant
 Know the chemical formulas of each reactant
 “Swap” ions
 Know the solubility rules
Potassium Chromate
(yellow)
Silver Nitrate
(clear solution)
What is the red precipitate?
Week 3
CHEM 1310 - Sections L and M
5
Predicting ID of Precipitant
 Know the chemical formulas of each reactant
 “Swap” ions
 Know the solubility rules
K2CrO4
AgNO3
2 K+
and
1 Ag+ and
1 CrO421 NO3-
Products: Ag2CrO4 and KNO3
What is the red precipitate?
Week 3
CHEM 1310 - Sections L and M
6
3
Solubility Rules
Table 4.1 from Text - VERY IMPORTANT!
Week 3
CHEM 1310 - Sections L and M
7
Predicting ID of Precipitant
 Know the chemical formulas of each reactant
 “Swap” ions
 Know the solubility rules
K2CrO4
AgNO3
2 K+
and
1 Ag+ and
1 CrO421 NO3-
Products: Ag2CrO4 and KNO3
What is the red precipitate?
Ag2CrO4
Week 3
CHEM 1310 - Sections L and M
8
4
Chemical Equations
How would one write a balanced chemical equation describing
the precipitation reaction shown?
K2CrO4 + AgNO3
Ions Reacting
2 mol K+
1 mol CrO421 mol Ag+
1 mol NO3-
Ag2CrO4 + KNO3
Ions in Products
1 mol K+
1 mol CrO422 mol Ag+
1 mol NO3-
Balance ions by visual inspection…
Week 3
CHEM 1310 - Sections L and M
9
Chemical Equations
How would one write a balanced chemical equation describing
the precipitation reaction shown?
K2CrO4 + 2AgNO3
Ag2CrO4 + 2KNO3
Ions Reacting
2 mol K+
1 mol CrO422 mol Ag+
2 mol NO3-
Ions in Products
2 mol K+
1 mol CrO422 mol Ag+
2 mol NO3-
Balanced
Week 3
CHEM 1310 - Sections L and M
10
5
Types of Acids and Bases
Arrhenius Acids and Bases
•
Acids are H+ donors
•
Bases are OH- donors
Arrhenius Broadened Definition
•
•
Week 3
Putting brackets
around a term
means
“concentration of”
the term
Acids increase [H+]
Bases increase [OH-]
CHEM 1310 - Sections L and M
11
Acid-Base Titrations
What is a titration?
Systematic addition of a
reagent until all of another
reagent is consumed.
Detection is visual
Indicator = Phenolphthalein
Acidic pH - Colorless
Neutral pH - Pink
Week 3
CHEM 1310 - Sections L and M
Base
Acid
12
6
Acid-Base Titrations
What is [NaOH] when 37.65 mL of NaOH are used to
titrate 0.6135g of KHC8H4O4?
Known Information
• # mol NaOH = # mol KHC8H4O4
• [NaOH] = # mol NaOH / vol soln
• Vol Soln = 37.65 x 10-3L
0.6135 g X
[NaOH] =
Week 3
1 mol KHC8H4O4
204.22g KHC8H4O4
3.004 x 10-3 mol
37.65 x 10-3 L
= 3.004 x 10-3 mol
= 0.07979 M NaOH
CHEM 1310 - Sections L and M
13
Acid & Base Titrations
EXAMPLE 4-10 from Text
What volume of 0.100 M HCl is needed to neutralize
25.0 mL of a 0.350 M NaOH solution?
• Write a balanced chemical equation from the word
problem
• Use rules of stoichiometry to relate terms
• Solve via calculation
Week 3
CHEM 1310 - Sections L and M
14
7
Redox Reactions
Redox: a class of reactions characterized by the transfer of electrons.
0
0
+2 -2
2 Mg(s) + O2(g) → 2 MgO(s)
↓ loss
↑ gain
2 x 2e- = 1 x 2 x 2e-
Magnesium is oxidized: it gives up electrons as the charge
on its atoms increases from 0 to +2.
Oxygen is reduced: it gains electrons as the charge on its
atoms decreases from 0 to -2 (i.e., becomes more negative).
Week 3
CHEM 1310 - Sections L and M
15
Oxidation Number
STUDY Table 4.3
Week 3
CHEM 1310 - Sections L and M
16
8
Oxidation Number
Oxidation Numbers (also called oxidation states) are determined
for the atoms in covalently bonded compounds by applying the
following set of 3 simple rules:
1. The oxidation number of the atoms in a neutral
molecule must all up to 0;
those in an ion must add up to the charge on
the ion.
Week 3
CHEM 1310 - Sections L and M
17
Oxidation Number
Oxidation Numbers (also called oxidation states) are determined
for the atoms in covalently bonded compounds by applying the
following set of simple rules:
2. Alkali metal (Group I) atoms have oxidation
number +1,
alkaline earth (Group II) atoms have oxidation
number +2 in their compounds;
atoms of Group III elements usually have
oxidation number +3 in their compounds.
Week 3
CHEM 1310 - Sections L and M
18
9
Oxidation Number
Oxidation Numbers (also called oxidation states) are determined
for the atoms in covalently bonded compounds by applying the
following set of simple rules:
3. Fluorine always has an oxidation number of -1
in its compounds.
The other halogens have oxidation number -1
in their compounds, except in compounds with
oxygen and with other halogens, in which they
can have positive oxidation numbers.
Week 3
CHEM 1310 - Sections L and M
19
Nomenclature for Redox Rxns
Oxidation Number
Change
Electron
Change
Oxidation
Increase
Loss of
Electrons
Reduction
Decrease
Gain of
Electrons
Oxidizing Agent,
does the oxidizing
Decrease
Picks Up
electrons
Reducing Agent,
does the reducing
Increase
Supplies
Electrons
Substance Oxidized
Increase
Loses
Electrons
Substance Reduced
Decrease
Gains
Electrons
Term
Week 3
CHEM 1310 - Sections L and M
20
10
Summary
 Know meanings of terms
 Know how to predict a precipitate
 Be able to calculate terms related to acid-base
titrations
 Determine oxidation state of an atom
 Write and balance chemical equations for
precipitation, acid-base rxns and redox rxns
Week 3
CHEM 1310 - Sections L and M
21
Study Tips
Read text
Work problems from text
Take practice exams online
Review lecture notes
Exam #1
Friday, Sep 14
Need
#2 Pencil
Calculator
Crib Sheet
Study in groups
Week 3
CHEM 1310 - Sections L and M
22
11