3.2 - redox reactions

    Cards (22)

    • What is the half equation for acidified manganate(VII) ions?
      MnO4–(aq) + 8H+(aq) + 5e–Mn2+(aq) + 4H2O(l)
    • What colour change occurs with acidified manganate(VII) ions?
      Purple to colourless
    • What is the half equation for acidified dichromate ions?
      Cr2O7 2–(aq) + 14H+(aq) + 6e– ⇌ 2Cr3+(aq) + 7H2O(l)
    • What colour change occurs with acidified dichromate ions?
      Orange to green
    • What is the half equation for iodine to iodide ions?
      I2(aq) + 2e– ⇌ 2I–(aq)
    • What colour change occurs when iodine is reduced to iodide ions?
      Brown to colourless
    • What is the half equation for thiosulfate ions?
      2S2O3 2–(aq) ⇌ S4O6 2–(aq) + 2e–
    • What is the process involving aqueous dichromate ions and iron(II) ions?
      • Cr2O7 2–(aq) oxidises Fe2+(aq)
      • Requires an indicator
      • Reaction: Cr2O7 2– + 14H+ + 6Fe2+ ⇌ 2Cr3+ + 7H2O + 6Fe3+
    • Why is the interconversion of dichromate and chromate ions not considered redox?
      Chromium does not change its oxidation number
    • What is the colour change when dichromate ions convert to chromate ions?
      Orange to yellow
    • What is the process involving aqueous thiosulfate ions and iodine?
      • S2O3 2– oxidised by I2
      • S2O3 2– in burette, I2 in flask
      • Colour fades to pale-yellow, then starch added
      • End point: blue colour decolourised
    • What is the reaction between iodide ions and copper(II) ions?
      2Cu2+(aq) + 4I–(aq) → 2CuI(s) + I2(aq)
    • What happens to the blue solution when iodide ions react with copper(II) ions?
      It loses its colour, forming a white precipitate
    • What is the procedure for standardising potassium manganate(VII) solution?
      • Titrated with iron(II) ammonium sulfate
      • MnO4– in burette, Fe2+ in flask
      • Excess sulfuric acid added
      • No indicator needed; pink colour indicates endpoint
    • What is the half equation for iron(II) ions oxidising to iron(III) ions?
      Fe2+(aq) ⇌ Fe3+(aq) + e–
    • What is the overall ionic equation combining half equations for Fe2+ and MnO4–?
      • MnO4– + 8H+ + 5Fe2+Mn2+ + 4H2O + 5Fe3+
    • How do you calculate the concentration of KMnO4 solution in mol dm–3?
      Use moles of Fe2+ and titration volume
    • What is the molar mass of FeSO4.7H2O?
      278.0 g/mol
    • How many moles of FeSO4.7H2O are in 25.00 g?
      0.089330.08933
    • What is the concentration of Fe2+ ions in the solution?
      0.08993 mol dm30.08993 \text{ mol dm}^{-3}
    • How many moles of MnO4– are in 25.55 cm3?
      4.496×1044.496 \times 10^{-4}
    • What is the concentration of the KMnO4 solution?
      0.0176 mol dm30.0176 \text{ mol dm}^{-3}
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