Free Printable Oxidation Numbers Worksheets - Free Printable

To find the oxidation numbers, we follow a few simple rules:
1. Neutral Compounds: The sum of all oxidation numbers must equal 0.
2. Ions (Charged compounds): The sum of all oxidation numbers must equal the charge of the ion.
3. Common Elements:
* Oxygen is usually -2.
* Hydrogen is usually +1 (except when bonded to metals).
* Group 1 metals (like K) are always +1.
* Group 2 metals (like Ca) are always +2.
* Halogens (like Cl, I) are usually -1 when at the end of a formula.
* Pure elements (like $O_2$ or $S_8$) are always 0.

Here is the step-by-step breakdown for each compound:

1. $\text{Ag}_2\text{S}$: Sulfur is in Group 16, so it is -2. To balance two Silver (Ag) atoms against one -2 charge, each Ag must be +1. ($+1 \times 2) + (-2) = 0$.
2. $\text{Al}_2\text{O}_3$: Aluminum is in Group 13, so it is +3. Oxygen is -2. Check: $(+3 \times 2) + (-2 \times 3) = 6 - 6 = 0$.
3. $\text{Ca}_3\text{P}_2$: Calcium is in Group 2, so it is +2. To balance three Ca atoms ($+6$ total), the two Phosphorus (P) atoms must total -6. So, each P is -3.
4. $\text{ClO}_3^-$: This is an ion with a -1 charge. Oxygen is -2. Three oxygens equal -6. We need the total to be -1. So, Chlorine (Cl) must be +5. ($+5 - 6 = -1$).
5. $\text{HI}$: Hydrogen is +1. Iodine is a halogen at the end, so it is -1. Sum is 0.
6. $\text{HNO}_2$: Hydrogen is +1. Oxygen is -2 (two oxygens = -4). Total so far is -3. To make the sum 0, Nitrogen (N) must be +3.
7. $\text{H}_3\text{O}^+$: This is an ion with a +1 charge. Hydrogen is +1 (three hydrogens = +3). Oxygen is -2. Sum: $+3 - 2 = +1$. Correct.
8. $\text{KMnO}_4$: Potassium (K) is +1. Oxygen is -2 (four oxygens = -8). Total negative is -8, plus K's +1 makes -7. Manganese (Mn) must be +7 to make the sum 0.
9. $\text{N}_2\text{H}_4$: Hydrogen is +1 (four hydrogens = +4). To balance this, the two Nitrogen (N) atoms must total -4. So, each N is -2.
10. $(\text{NH}_4)_2\text{SO}_4$: This has two parts.
* In Ammonium ($\text{NH}_4^+$): H is +1 (total +4). N must be -3 to make the ion charge +1.
* In Sulfate ($\text{SO}_4^{2-}$): O is -2 (total -8). S must be +6 to make the ion charge -2.
11. $\text{O}_2$: This is a pure element. Its oxidation number is 0.
12. $\text{S}_8$: This is a pure element. Its oxidation number is 0.
13. $\text{S}_2\text{O}_3^{2-}$: This is an ion with a -2 charge. Oxygen is -2 (three oxygens = -6). We need the total to be -2. So, the two Sulfur (S) atoms must total +4. Each S is +2.
14. $\text{SnCl}_4$: Chlorine is -1 (four chlorines = -4). Tin (Sn) must be +4 to balance it.

Final Answer:

| Compound | Oxidation Numbers of Each Element |
| :--- | :--- |
| $\text{Ag}_2\text{S}$ | Ag: +1, S: -2 |
| $\text{Al}_2\text{O}_3$ | Al: +3, O: -2 |
| $\text{Ca}_3\text{P}_2$ | Ca: +2, P: -3 |
| $\text{ClO}_3^-$ | Cl: +5, O: -2 |
| $\text{HI}$ | H: +1, I: -1 |
| $\text{HNO}_2$ | H: +1, N: +3, O: -2 |
| $\text{H}_3\text{O}^+$ | H: +1, O: -2 |
| $\text{KMnO}_4$ | K: +1, Mn: +7, O: -2 |
| $\text{N}_2\text{H}_4$ | N: -2, H: +1 |
| $(\text{NH}_4)_2\text{SO}_4$ | N: -3, H: +1, S: +6, O: -2 |
| $\text{O}_2$ | O: 0 |
| $\text{S}_8$ | S: 0 |
| $\text{S}_2\text{O}_3^{2-}$ | S: +2, O: -2 |
| $\text{SnCl}_4$ | Sn: +4, Cl: -1 |