Flashcards · 7405 · AS Topic 7

Oxidation, reduction and redox equations (AS Level) flashcards

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Oxidation and reduction (electron definitions): Oxidation: the process of electron loss. Reduction: the process of electron gain.
Oxidising agent and reducing agent: Oxidising agent: an electron acceptor (it is reduced). Reducing agent: an electron donor (it is oxidised).
Oxidation state of H in NaH, and of O in H₂O₂: H in metal hydrides: −1. O in peroxides: −1.
Oxidation state of Cl in ClO₃⁻: x + 3(−2) = −1, so x = +5.
Oxidation states of Mn in MnO₄⁻ and Cr in Cr₂O₇²⁻: Mn +7 in MnO₄⁻. Cr +6 in Cr₂O₇²⁻.
Steps to balance a half-equation in acid: Balance the element that changes oxidation state; balance O with H₂O; balance H with H⁺; balance charge with e⁻.
Half-equation: NO₃⁻ to NO₂ in acid: NO₃⁻ + 2H⁺ + e⁻ → NO₂ + H₂O (N goes from +5 to +4: reduction).
How do you combine two half-equations into an overall equation?: Scale them so electrons lost = electrons gained, add, then cancel electrons and any H⁺ and H₂O that appear on both sides. Check atoms and charge.