Oxidation, reduction and electron transfer

## Big idea: oxidation, reduction and electron transfer - **Key concept: Change.** Oxidation is loss of electrons and reduction is gain of electrons. In a displacement reaction, the more reactive metal is oxidised and the metal ions are reduced. - **Related concepts: Models and evidence.** Use a scientific explanation to make predictions, then test it against observations. - **Global context: Scientific and technical innovation.** Redox reactions underpin metal extraction and electrochemical cells. ## Oxidation & Reduction (Oxygen Definition) - **Oxidation** is the gain of oxygen by an element or compound. - **Reduction** is the loss of oxygen from an element or compound. - A **redox reaction** is one where oxidation and reduction occur simultaneously. - Example: ZnO + C → Zn + CO – zinc oxide is reduced (loses O), carbon is oxidised (gains O). ## Oxidation & Reduction (Electron Definition – Extended) - **Oxidation** is the loss of electrons; **reduction** is the gain of electrons (OIL RIG). - Oxidation increases the oxidation number; reduction decreases it. - Half-equations show electron transfer: e.g., Ag → Ag⁺ + e⁻ (oxidation); O₂ + 4e⁻ → 2O²⁻ (reduction). - Example: Fe + Cu²⁺ → Fe²⁺ + Cu – Fe loses electrons (oxidised), Cu²⁺ gains electrons (reduced). ## Oxidation Numbers & Roman Numerals - **Oxidation number** (state) shows the charge an atom would have if electrons were completely transferred. - Roman numerals in names indicate oxidation number: e.g., iron(II) = Fe²⁺, iron(III) = Fe³⁺. - Rules: uncombined elements = 0; monatomic ion = its charge; sum in compound = 0; sum in ion = charge. - Group 1 always +1, Group 2 always +2, F always –1, H usually +1, O usually –2. ## Identifying Redox Reactions by Colour Changes - **Potassium manganate(VII)** (KMnO₄) is a purple oxidising agent; with a reducing agent it turns colourless. - **Potassium iodide** (KI) is a colourless reducing agent; with an oxidising agent it turns red-brown (I₂ formed). - These colour tests are used to detect oxidising or reducing agents. ## Oxidising & Reducing Agents - An **oxidising agent** oxidises another substance and is itself reduced (gains electrons). - A **reducing agent** reduces another substance and is itself oxidised (loses electrons). - Common oxidising agents: O₂, Cl₂, KMnO₄, H₂O₂. Common reducing agents: C, H₂, KI. - Example: CuO + H₂ → Cu + H₂O – CuO is oxidising agent (reduced), H₂ is reducing agent (oxidised). ## Displacement Reactions & Redox - In displacement reactions, the more reactive metal loses electrons (oxidised) and the less reactive metal ion gains electrons (reduced). - Example: Fe + CuSO₄ → FeSO₄ + Cu – Fe is oxidised, Cu²⁺ is reduced. - Ionic equation: Fe + Cu²⁺ → Fe²⁺ + Cu. ## Half-Equations & Balancing - Half-equations show either oxidation or reduction separately with electrons. - Oxidation half: atoms/ions lose electrons (e.g., Ni → Ni²⁺ + 2e⁻). - Reduction half: atoms/ions gain electrons (e.g., Ni³⁺ + e⁻ → Ni²⁺). - Balance atoms and charge: e.g., O₂ + 4e⁻ → 2O²⁻. ## Extraction of Metals & Redox - Carbon is used to reduce metal oxides (e.g., ZnO + C → Zn + CO). - The metal oxide is reduced (loses oxygen), carbon is oxidised (gains oxygen). - Metals below carbon in the reactivity series can be extracted by reduction with carbon. ## Think like a scientist - Compare teacher-provided observations of different metals placed in the same copper sulfate solution. - **Comparison:** the metal placed in the solution. **Outcome:** whether copper forms and the solution colour changes. - **Control:** keep solution concentration and exposed metal area constant. Explain why this makes the comparison fairer. - **Evidence:** Use a consistent method, repeated observations where appropriate and a table with labelled quantities and units. Keep unexpected results and investigate their cause. - **Safety:** Practical activities need teacher supervision and an appropriate risk assessment. Use the provided data or simulation where the investigation specifies it. - **Inquiry task:** State a testable question, predict the outcome using the science, then explain how your observations would support or challenge the prediction. ## Evaluate the science - Redox reactions underpin metal extraction and electrochemical cells. - A colour change supports a reaction but does not identify every product without further tests. - **Evaluation task:** Link your conclusion to evidence, identify a limitation and suggest a specific improvement. Distinguish a measured result from an explanation of its cause.