electrolysis of aq

• Rules:

  • aq always have water
  • Some water molecules split into H and OH ions which participate in electrolysis reactions

  +ve Electrode

  • Negatively charged OH ions & non-metal ions attracted to positive electrode
  • If halide ions & OH are present: halide is discharged @ anode, lose electrons -> halogen
  • otherwise OH discharged, lose electrons -> oxygen
  • the other -ve ion remains in solution

  -ve Electrode

  • H ions & metal ions attracted to negative electrode but only one will gain electrons
  • H OR metal produced
  • If metal is above H in reactivity series, H produced – bubbling
• Electrolysing aqueous solution where there are gaseous products

  • The apparatus can be modified for the collection of gases by using inverted test tubes over the electrodes
  • The electrodes are made from graphite which is inert and does not interfere with the electrolysis reactions

  A) electrolyte

  B) inverted

  C) gases

  
• • CuCl2: Cu below H -> copper(II) ions preferentially discharged @ cathode; chlorine = halogen, preferentially discharged @ anode
  • NaCl: Na above H -> H+ ions discharged cathode; chlorine = halogen, discharged anode
  • Na2So4: Na above H -> H+ discharged cathode; OH- ions preferentially discharged over sulfate ions, so oxygen is produced at the anode
  • acidified water: H+ ions are discharged at the cathode; oxygen frm water molecules @ anode

  A) chlorine

  B) hydrogen

  C) chlorine

  D) lower

  E) hydrogen

  F) oxygen

  G) hydrogen

  H) oxygen

  I) h2o

  J) hydrogen

  
• At the cathode (negative electrode), reduction reactions occur. Here, less reactive ions are more likely to gain electrons and undergo reduction (gain of electrons). For example, in the electrolysis of water, hydrogen ions (H⁺) are less reactive compared to hydroxide ions (OH⁻). So, H⁺ ions are preferentially reduced to form hydrogen gas (H₂) rather than OH⁻ ions being reduced to oxygen gas (O₂).
• Similarly, at the anode (positive electrode), oxidation reactions take place. Less reactive ions are more willing to lose electrons and undergo oxidation (loss of electrons). For example, in the electrolysis of copper(II) sulfate solution, copper ions (Cu²⁺) are less reactive compared to sulfate ions (SO₄²⁻). So, Cu²⁺ ions are preferentially oxidized to form copper metal (Cu) rather than SO₄²⁻ ions being oxidized to form oxygen gas (O₂).
• • Higher standard electrode potential: ion more likely to gain electrons, undergo reduction. It's not about being higher in the reactivity series; it's about the ion's affinity for gaining electrons. higher potential = greater tendency to accept electrons & be reduced bc it's more energetically favorable for it.
  • Lower standard electrode potential: ions more likely to lose electrons, undergo oxidation. not that theyre less reactive, but they have less of a tendency to accept electrons. more willing to give up electrons to become stable bc it's energetically favorable.