Electrolysis of aqueous solutions

• In the electrolysis of aqueous solutions, the water molecules dissociate producing H+ and OH– ions:

  H2O ⇌ H+ + OH–
• • Negatively charged OH– ions and non-metal ions are attracted to the positive electrode
• If halide ions and OH- are present then the halide ion is discharged at the anode, loses electrons and forms a halogen
• If no halide ions are present, then OH- is discharged at the anode, loses electrons and forms oxygen
• • Positively charged H+ and metal ions are attracted to the negative electrode but only one will gain electrons
• • If the metal is above hydrogen in the reactivity series, then hydrogen will be produced and bubbling will be seen at the cathode
• This is because the more reactive ions will remain in solution, causing the least reactive ion to be discharged
• Therefore at the cathode, hydrogen gas will be produced unless the positive ions from the ionic compound are less reactive than hydrogen, in which case the metal is produced