Download Electrons

Introduction
to Oxidation and Reduction
IB Chemistry Text
Green and Damji
TEXT 9.1 & 9.2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Types of Chemical Reactions ?
type of
reaction ?
1. Mg(s) + 2 HCl (aq)  MgCl2 (aq) + H2 (g)
2. Pb(NO3)2 (aq) + 2 NaI (aq)  PbI2 (s) + 2 NaNO3 (aq)
3. 2 H2O2 (aq)  O2 (g) + 2 H2O (g)
4. 2 O2 (g) + CH4 (g)  CO2 (g) + 2 H2O (g)
5. 2 H2 O (g)  O2 (g) + H2(g)
another way to classify
Types of Chemical Reactions
A. Acid Base Reactions
CaO (s) + 2 HCl (aq)  CaCl2 (aq)
+ H2O
H3PO4 (aq) + 3 NaOH (aq)  Na3PO4 (aq)
(l)
+ 3 H2O
B. Precipitation Reactions
Pb(NO3)2 (aq) + 2NaI (aq)
PbI2 (s) + 2NaNO3 (aq)
which can be shortened to…Pb2+ + 2I-
C. Redox Reactions
2 Zn (s) + I2 (s)
ZnI2 (aq)
2 Zn (s) + I2 (s)
Zn2+ (aq) + 2 I- (aq)
PbI2 (s)
(l)
Classify the following reactions as AB/PPT/RedOx
Ca2+ + CO32NH3 + H+
Zn + 2HCl
Ca + F2
CaCO3
NH4+
ZnCl2 + H2
CaF2
________________
________________
________________
________________
4.4
Oxidation-Reduction Reactions
(electron transfer reactions)
2Mg + O2
2MgO
What is happening in this reaction?
oxidation – loss of electrons:
reduction – gain of electrons:
4.4
Helpful Mneumonics
LEO the lion goes GER
Loss of Electrons is Oxidation
Gain of Electrons is Reduction
OIL RIG
Oxidation is the Loss of electrons
Reduction is the Gain of electrons
Oxidation number
The charge the atom would have in a molecule (or an
ionic compound) if electrons were completely transferred
to the more electronegative element.
1. Free elements (uncombined state) have an oxidation
number of zero.
Na, Be, K, Pb, H2, O2, P4 =
2. In monatomic ions, the oxidation number is equal to
the charge on the ion.
Li+, Li =
; Fe3+, Fe =
; O2-, O =
3. The oxidation number of oxygen is usually
and O22- it is .
. In H2O2
4.4
4. The oxidation number of hydrogen is____except when
it is bonded to metals in binary compounds. In these
cases, its oxidation number is____.
5. Group 1 metals are____, Group 2 metals are____and
fluorine is always____.
6. The sum of the oxidation numbers of all the atoms in a
molecule or ion is equal to the charge on the
molecule or ion.
7. Oxidation numbers do not have to be integers.
Oxidation number of oxygen in the superoxide ion,
O2-, is ____.
-
HCO3
Oxidation numbers of all
the elements in HCO3- ?
O = ____ H = ____
3x(-2) + 1 + ? = -1
C = ____
4.4
The oxidation numbers of elements in their compounds
The periodic table in
your planner
includes the most
common oxidation
numbers!
4.4
I F7
What are the oxidation
numbers of all the elements
in the following compounds ?
F = ____
7x(____) + ? = 0
I = ____
K2 Cr2 O7
Na I O3
Na = ____
O = ____
3x(____) + ____ + ? = 0
I = ____
O = ____ K = ____
7x(__) + 2x(__) + 2x(?) = 0
Cr = ____
4.4
More to know…
An increase in oxidation number is oxidation.
A decrease in oxidation number is reduction.
The substance that is oxidized (loses e-; ox # increases)
is called the reducing agent.
The substance that is reduced (gains e-; ox # decreases)
is called the reducing agent.
Zn (s) + CuSO4 (aq)
ZnSO4 (aq) + Cu (s)
ox:
red:
--------------------------------------ttl:
____ is oxidized - is reducing agent
____ is reduced - is oxidizing agent
4.4
Copper wire reacts with
silver nitrate to form silver
metal.
What is the oxidizing
agent in the reaction?
ox:
red:
--------------------------------------ttl:
____ is oxidized - is reducing agent
____ is reduced - is oxidizing agent
4.4
Types of Oxidation-Reduction Reactions
Combination Reaction (aka Synthesis)
A+B
0
C
+3 -1
0
2Al + 3Br2
2AlBr3
Decomposition Reaction
C
+1 +5 -2
2KClO3
A+B
+1 -1
0
2KCl + 3O2
4.4
Types of Oxidation-Reduction Reactions
Combustion Reaction
A + O2
B
0
0
S + O2
2Mg + O2
0
0
+4 -2
SO2
2MgO
+2 -2
4.4
Types of Oxidation-Reduction Reactions
Single Displacement Reaction
A + BC
0
+1
+2
Sr + 2H2O
+4
0
TiCl4 + 2Mg
0
AC + B
-1
Cl2 + 2KBr
0
Sr(OH)2 + H2 Hydrogen Displacement
0
+2
Ti + 2MgCl2
-1
Metal Displacement
0
2KCl + Br2
Halogen Displacement
4.4
Types of Oxidation-Reduction Reactions
Disproportionation Reaction
Element is simultaneously oxidized and reduced.
0
Cl2 + 2 OH-
+1
-1
ClO- + Cl- + H2O
Chlorine Chemistry
4.4
Chemistry in Action: Metals from the Sea
Redox or not?
CaCO3 (s)
CaO (s) + CO2 (g)
CaO (s) + H2O (l)
Ca2+ (aq) + 2OH- (aq)
Mg2+ (aq) + 2OH - (aq)
Mg(OH)2 (s) + 2HCl (aq)
MgCl2 (aq)
Mg(OH)2 (s)
_______________
_______________
_______________
MgCl2 (aq) + 2H2O (l) ____________
Mg (s) + Cl2 (g)
_______________
Write half reactions for one of the redox reactions above:
ox:
red: