The Nature Of Science And Engineering, Physical Science Worksheet With Answers - Minnesota K-12 Page 7
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12b. Polyatomic elements have an oxidation number of zero for each atom.
Elements such as H
, O
, and P
share electrons equally among all atoms in the
2
2
4
molecule.
c. The sum of the oxidation numbers in a neutral molecule is zero.
d. A monatomic ion has an oxidation number equal to its charge. For example,
2-
the oxidation number of the oxygen in the oxide ion, O
, is –2.
e. The sum of the oxidation numbers in a polyatomic ion is equal to the charge
on the ion.
f. The oxidation number for an oxygen ion is –2. The oxidation number for a
hydrogen ion is +1. (These are general rules that apply to a wide variety of
reactions. We will not consider the exceptions to this rule in this activity).
19. Using the reactions given as references at the beginning of this phase:
a. What happened to the oxidation number of iron in the first reaction?
0 → 3+
b. What happened to the oxidation number of copper in the second reaction?
0 → 1+
c. What happened to the oxidation number of magnesium in the third
reaction?
0 → 2+
20. Do you notice a trend or pattern for the changes in oxidation numbers from
the previous problem?
The pattern is that the oxidation numbers of the metals increase.
21. Let’s called this trend oxidation. Use the following equation as another
example to consider this term. What happens to iron in reaction four? Is there a
general trend that can be stated for any species that is oxidized?
IV. 2 Fe + 3 Cl
→ 2 FeCl
2
3
Oxidation number goes from 0 to 3+ (Number is still increasing-becoming more
positive; just as before.)
22. Now, return your attention to the original three reactions given as a reference
in this phase.
a. What happened to the oxidation number of oxygen in the first reaction?
0 → 2
b. What happened to the oxidation number of oxygen in the second reaction?
0 → 2-
c. What happened to the oxidation number of oxygen in the third reaction?
0 → 2-
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