3.2 Redox reactions

    Cards (10)

    • Balancing half equations in acidic conditions:
      • add H2O, H+ and then electrons
    • Balancing half equations in alkaline conditions:
      • add H2O to the side that already has oxygen, OH- to opposite side and then electrons to balance charge
    • Combining half equations - multiply one or both equations so that the number of electrons on each side is the same and they can cancel out
    • Concordant titre results are within 0.20 cm3 of each other
    • MnO4- to Mn2+ = purple to pale pink
    • CrO7 2- to 2Cr3+ = orange to green
    • Fe2+ to Fe3+ = pale green to pale yellow
    • I2 to 2I- = brown to colourless (blue-black to colourless if starch is added)
    • 1 mole of Cu2+ = 1 mole of S2O3 2-
    • To determine concentration of Cu2+ ions
      • 1st reaction - 2 moles of Cu2+ form 1 mole of brown I2
      • 2nd reaction - add thiosulfate ions to reduce I2 to I-, starch indicator to determine end point (blue black to colourless) 1 mole of I2 react with 2 moles of S2O3 2-
      • Therefore 1 mole of Cu2+ is equivalent to 1 mole of S2O3 2-