Flashcards · 9620 · AS Topic 5

Oxidation, reduction and redox equations (AS Level) flashcards

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Oxidation and reduction (in terms of electrons): Oxidation is the process of electron loss. Reduction is 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 rules for F, H and O in compounds: F: always −1. H: +1, but −1 in metal hydrides (such as LiH). O: −2, but −1 in peroxides and positive when bonded to F.
Oxidation state of P in P₄O₁₀ and of S in Na₂S₂O₅: P: 4x + 10(−2) = 0, so +5. S: 2(+1) + 2x + 5(−2) = 0, so +4.
Steps to balance a half-equation in acidic solution: Balance the element that changes, then O with H₂O, then H with H⁺, then charge with e⁻. Example: IO₄⁻ + 2H⁺ + 2e⁻ → IO₃⁻ + H₂O
How do you combine two half-equations into a redox equation?: Scale them so electrons lost = electrons gained, add them, then cancel the electrons and any H⁺ or H₂O that appear on both sides. Check atoms and total charge.
Is SO₃ + H₂O → H₂SO₄ a redox reaction?: No. S is +6 on both sides, H stays +1 and O stays −2. No oxidation state changes.
Oxidation state +2 vs ionic charge 2+: An oxidation state is written sign first (+2); the charge on an ion is written number first (2+).