Step-by-Step Examples for Assigning Oxidation States in Compounds

📚 Quick Study Guide

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• Oxidation State Basics: The oxidation state represents the hypothetical charge an atom would have if all bonds were completely ionic.
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• Rules for Assigning Oxidation States:
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  • Atoms in their elemental form have an oxidation state of 0 (e.g., $O_2$, $Cu$).
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  • Monatomic ions have an oxidation state equal to their charge (e.g., $Na^+$ has an oxidation state of +1, $Cl^-$ has an oxidation state of -1).
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  • Oxygen usually has an oxidation state of -2 (except in peroxides like $H_2O_2$, where it's -1, or when bonded to fluorine).
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  • Hydrogen usually has an oxidation state of +1 (except when bonded to metals in binary compounds, where it's -1).
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  • Fluorine always has an oxidation state of -1.
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  • The sum of the oxidation states in a neutral compound is 0, and in a polyatomic ion, it equals the ion's charge.
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• Using Algebra: Set up an equation where the sum of the oxidation states equals the overall charge. Solve for the unknown.

🧪 Practice Quiz

1. What is the oxidation state of sulfur (S) in $H_2SO_4$?
1. A) +2
2. B) +4
3. C) +6
4. D) -2
2. What is the oxidation state of chromium (Cr) in $K_2Cr_2O_7$?
1. A) +3
2. B) +6
3. C) +12
4. D) -2
3. What is the oxidation state of oxygen in $OF_2$?
1. A) -2
2. B) +2
3. C) -1
4. D) +1
4. What is the oxidation state of manganese (Mn) in $KMnO_4$?
1. A) +2
2. B) +4
3. C) +6
4. D) +7
5. What is the oxidation state of carbon (C) in $CO_3^{2-}$?
1. A) +2
2. B) +4
3. C) +6
4. D) -2
6. What is the oxidation state of nitrogen (N) in $NH_4^+$?
1. A) -3
2. B) +3
3. C) -4
4. D) +4
7. What is the oxidation state of iron (Fe) in $Fe_2O_3$?
1. A) +2
2. B) +3
3. C) -2
4. D) -3