Chem 30 Redox 6
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Mark # 3-5 on LSM 13.2 F after reviewing 1 and 2.
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Demo: Pennies in conc. HNO3. What do the colors tell us about the copper ion charges?
What is the gas produced?
Demo: Magic wand exp. How can we tell if the rxn is redox??. (p 158 Tik Liem)
C2H5OH(l) + MnO4-(aq)  CH3COOH(aq) + MnO2(s)
(unbalanced partial equation)
Oxidation States/Numbers
Some reactions (ie. Burning of fuels), may be difficult to determine if redox or not. Also,
these half reactions may not be listed in the data booklet. A system of electron
“bookkeeping” was developed.
**If the oxidation states/numbers of any atoms in the reaction change, a redox
reaction is present.
Rules:
1. All atoms in elements = 0
a. Eg. H2, Na, O2 etc..
2. Hydrogen in compounds = +1
a. Eg. H2CO3, H2O
3. Oxygen in compounds = -2
a. Eg. H2O, H2CO3
4. Monoatomic ions = charge on ion
a. Eg. NaCl, CaBr2
(except hydrides = -1)
eg. LiH
(except peroxides = -1)
eg. H2O2
●Polyatomic ions must always be considered separately, if present
●Coefficients are not considered when finding oxidation states (see #6 p. 589)
Eg. What is the oxidation state of each individual atom in: AgNO3, Cl2, Cr2O72- , 6 H+,
CH3COOH, Cu, C4H10?
Note: This is not OH-
●Now, determine if C2H5OH(l) in the magic wand exp. was reduced or oxidized. MnO4- ?
Remember always to compare the oxidation states of each individual atom on the
reactant side to the product side. Do not compare oxidation state totals.
Oxidation numbers and Redox rxns
If the oxidation number increases……………oxidation has occurred
If the oxidation number decreases…………..reduction has occurred
Eg. Breathalyzer reaction
Note that these
oxidation states
are for each
atom, not for
the unit.
Coefficients do
not affect the
oxidation
states.
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Assign # 6-9 p. 589
*For # 7, indicate if the reaction is a redox reaction or not and identify the OA and
the RA unit
Ie. In the reaction HNO3  N2
HNO3 is the OA, even though only the N of the HNO3 is the atom
gaining e-