Oxidation Numbers Worksheet
A Grade 9 Science worksheet on understanding and calculating oxidation numbers in chemical compounds and ions.
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Oxidation Numbers Worksheet
Name:
Date:
Score:
Read each question carefully and provide the best answer. Show all your work for calculation problems.
1. What is the oxidation number of oxygen in most compounds?
+1
-1
+2
-2
2. In a neutral compound, the sum of all oxidation numbers is:
Equal to the number of atoms
Zero
Always positive
Always negative
3. The oxidation number of an uncombined element is always .
4. In a polyatomic ion, the sum of the oxidation numbers of all atoms equals the of the ion.
5. Calculate the oxidation number of sulfur (S) in H₂SO₄.
6. Determine the oxidation number of chromium (Cr) in the dichromate ion, Cr₂O₇²⁻.
7. All elements in Group 1 (alkali metals) always have an oxidation number of +1 in their compounds.
True
False
8. Hydrogen always has an oxidation number of +1.
True
False
Match the compound/ion with the correct oxidation number for the underlined atom.
9. H₂S
a. +5
10. SO₂
b. -2
11. NO₃⁻
c. +4
12. Explain why understanding oxidation numbers is important in chemistry. Provide at least two reasons.
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