Redox Changes: Via Numbers
Oxidation Numbers • Redox Identification • Non-Redox Reasoning
Definitions
Define oxidation in terms of oxidation number.
Define reduction in terms of oxidation number.
Define a reducing agent in terms of oxidation number.
Define an oxidising agent in terms of oxidation number.
What is a redox reaction?
Application — Identifying Redox
In the reaction C + O₂ → CO₂, explain why carbon is oxidised in terms of oxidation number.
In the reaction Mg + 2HCl → MgCl₂ + H₂, identify which species is reduced. Justify your answer using oxidation numbers.
In the reaction Fe₂O₃ + 3CO → 2Fe + 3CO₂, which species is the reducing agent? Use oxidation numbers to justify your answer.
In the reaction 2Na + Cl₂ → 2NaCl, determine the oxidation number change for both sodium and chlorine and identify what type of reaction this is.
In the reaction Cu²⁺(aq) + Zn(s) → Cu(s) + Zn²⁺(aq), identify the oxidising agent and state its oxidation number change.
Identifying Non-Redox Reactions
Use oxidation numbers to explain why CaCO₃ → CaO + CO₂ is NOT a redox reaction.
Use oxidation numbers to explain why NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l) is NOT a redox reaction.
Use oxidation numbers to show that AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq) is NOT a redox reaction.
Use oxidation numbers to explain why H₂SO₄(aq) + CuO(s) → CuSO₄(aq) + H₂O(l) is NOT a redox reaction.
A student claims that Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂ is a redox reaction because CO₂ gas is produced. Use oxidation numbers to confirm or disprove this claim.
📐 Oxidation Number Rules — Quick Reference
🧠 OIL RIG — Never Forget This
OIL
Oxidation Is Loss (of electrons)
= Oxidation number INCREASES
RIG
Reduction Is Gain (of electrons)
= Oxidation number DECREASES
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