Oxidation Numbers – Practice with the Rules
ChemistryReactions & RedoxAges 15–16
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Reactions & Redox
Choose a compound or ion (KMnO₄, H₂SO₄, NH₄⁺, Fe₃O₄, K₂Cr₂O₇, H₂O₂, NaH, SO₄²⁻…), enter the oxidation number of each element and check: the simulation checks each value and verifies that the oxidation numbers add up to the charge. The step-by-step button applies the rules one at a time; a second tab gives sample reactions for identifying the oxidizing agent and the reducing agent and drawing the electron-transfer diagram.
Lesson: Oxidation numbers, oxidizing agents and reducing agents
What it shows
Oxidation numbers keep track of how electrons are shared or transferred in compounds and ions. They follow a short list of rules: free elements are 0, Group 1 and Group 2 metals are +1 and +2, hydrogen is usually +1, oxygen usually −2, fluorine always −1, and all oxidation numbers add up to the overall charge. Exceptions such as peroxides, metal hydrides and OF₂, and averages like +8/3 for iron in Fe₃O₄, test real understanding. In a redox reaction the reducing agent is oxidized, so its oxidation number rises, while the oxidizing agent is reduced.
How to use
On the Oxidation numbers tab, pick a compound or ion, type an oxidation number for each element and press Check; the sum line shows whether the values add up to the charge. Use Step by step to model the order in which the rules are applied, then press Start over and let students try alone. On the Reactions tab, choose the role of each reactant, check it and press Show electron diagram.
Parameters you can change
- Starting compound or ion KMnO₄, H₂SO₄, NH₄⁺, Fe₃O₄, K₂Cr₂O₇, H₂O₂, NaH, SO₄²⁻
- Sample reaction Fe + CuSO₄, KMnO₄ + concentrated HCl, Cu + concentrated H₂SO₄, NH₃ + O₂, Fe₂O₃ + CO, Decomposition of H₂O₂, Cl₂ + NaOH, Zn + HCl
- Allow step-by-step solutions and answers
- Opening tab Oxidation numbers, Reactions – oxidizing and reducing agents
Questions to explore
- Why is the oxidation number of oxygen −1 in H₂O₂ rather than −2?
- What does the oxidation number +8/3 for iron in Fe₃O₄ tell you about the iron ions present?
- In the reaction of KMnO₄ with concentrated HCl, why does only part of the HCl act as the reducing agent?
