2. Simple Redox Reactions
Decomposition, Combustion
*element all by itself means redox*
a. Potassium chlorate is heated.
2 KClO3  2 KCl + 3 O2
*watch the “Gummy Bear Sacrifice” video of the
decomposition of potassium chlorate, followed by
the combustion of the sucrose in a gummy bear at
http://www.youtube.com/watch?v=5gDCSwTV1Sg
What is the change in oxidation state of chlorine
during the reaction?
+5 to -1
b. Hydrogen peroxide is decomposed.
2 H2O2  2 H2O + O2
Identify the species being oxidized and the species
being reduced in the reaction.
H2O2 is both oxidized and reduced. This is an
example of a disproportionation reaction.
c. Sodium metal is burned in air.
4 Na + O2  2 Na2O
Identify the oxidizing and reducing agents in the
reaction. ox. agent = O2 ; red. agent = Na
d. Hydrogen chloride gas is oxidized by oxygen gas.
4 HCl + O2  2 H2O + 2 Cl2
If three moles of hydrogen chloride gas and three
moles of oxygen gas react as completely as
possible, which reactant, if any, is present in
excess? Justify your answer.
O2 is in excess; since HCl and O2 react in a 4:1
ratio, 12 mol of HCl would be required to react
with 3 mol of O2
e. A mixture of powdered aluminum and iron(III)
oxide is ignited.
(This is known as the “thermite reaction”)
2 Al + Fe2O3  2 Fe + Al2O3
Identify the species being oxidized and the species
being reduced in the reaction.
*Watch the video of this reaction at
http://www.youtube.com/watch?v=a8XSmSdvEK
4&feature=related
Al is oxidized
Single Replacement, (cation)
Fe2O3 is reduced
*charges must be equal on both sides*
f. A solution of copper(II) sulfate is spilled onto a
sheet of freshly polished aluminum metal.
2 Al + 3 Cu2+  3 Cu + 2 Al3+
Identify the oxidizing agent.
Cu2+
g. A strip of zinc is placed in a solution of nickel(II)
nitrate.
Zn + Ni2+  Ni + Zn2+
Which substance is oxidized?
Zn
h. Zinc metal is placed in a solution of copper(II)
sulfate.
Zn + Cu2+  Cu + Zn2+
Describe the change in color that the original
solution undergoes as the reaction proceeds.
The solution goes from blue to colorless as the Cu2+
ion leaves the solution.
i. A solution containing silver(I) ion (an oxidizing
agent) is mixed with a solution containing iron(II)
ion (a reducing agent).
+
Ag + Fe2+  Ag + Fe3+
If the contents of the reaction mixture described
above are filtered, what substance(s), if any, would
remain on the filter paper?
solid silver