Grade 12 Chemistry: Oxidation Numbers
A comprehensive worksheet for Grade 12 Chemistry students covering the rules for assigning oxidation numbers, calculating oxidation numbers in compounds and polyatomic ions, and identifying redox reactions.
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Oxidation Numbers Worksheet
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Read each question carefully and provide your answers in the space provided. Show all your work for calculations.
1. The oxidation number of an element in its free (uncombined) state is .
2. The oxidation number of a monatomic ion is equal to its .
3. In most compounds, hydrogen has an oxidation number of , but in metal hydrides, it is .
4. In most compounds, oxygen has an oxidation number of , but in peroxides, it is .
5. The sum of the oxidation numbers of all atoms in a neutral compound is .
6. The sum of the oxidation numbers of all atoms in a polyatomic ion is equal to the of the ion.
Determine the oxidation number of the bolded element in each of the following compounds or ions:
7. H₂S
8. SO₄²⁻
9. KMnO₄
10. Cr₂O₇²⁻
11. Na₂O₂
12. Which of the following reactions is a redox reaction?
NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)
HCl(aq) + NaOH(aq) → H₂O(l) + NaCl(aq)
2Na(s) + Cl₂(g) → 2NaCl(s)
CaCO₃(s) → CaO(s) + CO₂(g)
13. In a redox reaction, a substance that is oxidized gains electrons.
True
False
14. The oxidation number of an alkali metal in a compound is always +1.
True
False
15. Explain why the concept of oxidation numbers is important in chemistry.