Oxidation Number Tutorial

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Oxidation Number Tutorial

  • Pure elements oxidation state is ZERO
    e.g. P4 = 0
    e.g. O2 = 0
    e.g. Na = 0
  • Mon atomic ions have the same oxidation state as their charge
    e.g. O2- = -2
    e.g. Mg2+ = 2+
  • Oxygen nearly always = -2
  • H nearly always = +1
  • The sum of the oxidation states in a molecule is ZERO
    e.g. H2O ((2 x +1) + -2) = 0
    e.g. CO2 = (+4 + (2 x -2)) = 0
  • The most electronegative atom has the negative oxidation number
  • Maximum oxidation state = group number, except metals
    e.g. Oxygen (Group 6) Maximum Ox. State = +6 (most common Ox. state = -2)
    e.g. Fluorine (Group 7) Maximum Ox. State = +7 (most common Ox. state = -1)

Questioning

What is the oxidation state of the elements in ?
a) N
b) Fe3+
c) S2-
d) Cu
e) Cu2+
f) Cu+

What will be the common and maximum oxidation state of the elements listed below when they are in compounds?

  Common Maximum
Li    
O    
B    
N    
Cr    

Give the oxidation state of the element other than O, H or F in:
a) SO2
b) NH3
c) S2 O32-

What change takes place in the oxidation state of the bold element?
Classify the change as oxidation (O), reduction (R) or neither (N).
a) N O3¯ → N O
b) H N O3 → N _2 O
c) C H4 → C O

Balance the following half-equations:
a) MnO4- → Mn2+
b) SO2 → SO42-

Validate