GoalKnow redox reactions (OQR), and identify the oxidizing and reducing agents.
New words
redox reaction · oksidlanish-qaytarilish reaksiyasi (OQR)oxidizing agent · oksidlovchireducing agent · qaytaruvchioxidation and reduction · oksidlanish va qaytarilish
Explanation
Reactions in which the oxidation states of elements change are called redox reactions. Oxidation is the giving of electrons by an atom, molecule or ion, and the oxidation state rises; reduction is the accepting of electrons and the state falls. The particle that gives electrons is the reducing agent (it is oxidized), the particle that accepts them is the oxidizing agent (it is reduced). Both processes happen together: the number of electrons given equals the number accepted. Metals are only reducing agents; nonmetals (except fluorine) can be oxidizing or reducing depending on conditions: in 2Na + S → Na₂S sulfur is the oxidizing agent, in S + O₂ → SO₂ it is the reducing agent. Reactions with no change of oxidation states (e.g. NaOH + HCl → NaCl + H₂O) are not redox.
Worked examples
2Mg + O₂ → 2MgO: Mg⁰ → Mg²⁺ (state rises, Mg is the reducing agent), O⁰ → O²⁻ (falls, O₂ is the oxidizing agent).
H₂S + Cl₂ → 2HCl + S: S⁻² → S⁰ (reducing agent H₂S), Cl⁰ → Cl⁻ (oxidizing agent Cl₂). In CaCO₃ → CaO + CO₂ no state changes — not redox.
Class activity
“Redox or not?”: write 6 reaction equations on cards (e.g. 2H₂ + O₂ → 2H₂O, NaOH + HCl → NaCl + H₂O). Write the states and mark the oxidizing and reducing agents. On paper only; no reactions are carried out.
Practice
1
Define oxidation and reduction in terms of electrons.