Transcript Slide 1

USING OXIDATION NUMBERS
The three major uses for oxidation numbers are:
1 determining whether or not oxidation and reduction are involved in a chemical
reaction (as just explained)
2 naming compounds in a systematic way
3 balancing ‘diffi cult’ chemical equations.
The concept of oxidation numbers (states) allows us to extend this technique
to naming anions. Rather than using terms such as hypochlorite, chlorite, chlorate,
perchlorate, manganate or permanganate, which alone do not tell us the formula
of the anion, we can now name all oxyanions as -ates and put the oxidation state
(number) in brackets after it: chlorate(I), chlorate(III), chlorate(V), chlorate(VII),
manganate(VI) and manganate(VII) for the ions just named. These names tell
us the formulae of the anions: chlorate(I) must be ClO–, chlorate(III), ClO2
–,
chlorate(V), ClO3
–, manganate(VII), MnO4
– and so on. Unfortunately this
systematic naming of anions is less widely used than that for cations; hypochlorite
and permanganate, for example, are much more commonly used.
When discussing the chemistry of various elements we often talk in terms of their
oxidation states in order to avoid ambiguity. We refer to iron in the 2 or 3 state,
1,3,5, or 7 states or manganese in the
2, 3, 4, 6, or
7 states, even if we are still using names such
as hypochlorite or permanganate.
chlorine in the
EXERCISES
BALANCING REDOX REACTIONS
Ignore
this method
its difficult
Balancing using half reactions from a table
I would use this
higher
lower
C + O2
CO2
2Cl-
Cl2 + 2e-