Name_______________ Hr ___
Chapter 19: Oxidation and Reduction Reactions
Section 1
You can use rules to assign __________________ numbers.
Oxidation-reduction reactions involve a transfer of ________________. Oxidation involves
the __________ of electrons while reduction involves the __________ of electrons.
Rules for assigning oxidation numbers:
1.
The oxidation number is 0 for all elements in their pure elemental state.
Ex: O2, Zn, Ne
2.
Elements in Group 1A (alkali metals) are always +1
Ex: Na+1, Cs+1
3.
Elements in Group IIA (alkaline earth metals) are always +2
Ex: Ca+2, Ba+2
4.
Boron and Aluminum are always +3
5.
Halogens are always -1
Ex: I-1, Br-1
6.
Oxygen is usually -2, except in peroxides, (Na2O2) it is -1.
7.
Nitrogen and phosphorus are usually -3 in binary compounds.
8.
Hydrogen is usually +1, except as a hydride, then it is -1 (LiH)
9.
The sum of oxidation numbers of a neutral compound is zero.
Ex: FeCl3, Cl is -1 so Fe is +3
10.
In CO2, O is -2 so C is +4
The sum of the oxidation numbers of an ion is equal to the charge on the
ion. Ex: SO42- O is -2 so S is +6
Use the rules on the front to assign oxidation numbers to all atoms in each of the
following:
Ni3P2
Cr2O3
Cu
HCrO4
CO32-
P4
KMnO4
Cu2+
View Figure 1.2. Oxidation States of Chromium Compounds
How many different oxidation numbers of chromium are shown?___ What are they?________
What type of element is chromium?__________________ What physical property changes
with different oxidation numbers? __________________
Oxidation occurs when __________________ electrons are lost.
Processes in which the atoms or ions of an element experience an _____________ in oxidation
number are oxidation processes.
Consider the reaction between metallic sodium and chlorine gas:
2Na(s) + Cl2(g)  2 NaCl(s)
The formation of sodium ions is an oxidation process. Sodium is oxidized.
Write the “half-reaction” depicting sodium atoms becoming ions. Include oxidation numbers.
_____________________________
Reduction occurs when valence electrons are _______________.
Processes in which the oxidation number of an element ____________ are reduction processes.
The formation of chloride ions is a reduction process. Chlorine is reduced.
Write the “half-reaction” depicting chlorine atoms becoming ions. Include oxidation numbers.
_____________________________
For each of the following, write the half-reactions and label which element is oxidized and
which element is reduced.
a. 2Cu(s) + O2(g)2CuO(s)
b. 2Cs(s) + F2(g)  2CsF(s)