Electrolysis Aqueous Solutions

• What is electrolysis used for?

  To split compounds into their elements
• How is electrolysis performed?

  By passing an electric current through an electrolyte
• Why do ions in an electrolyte need to be free to move for electrolysis to work?

  Because they must conduct electricity to facilitate the reaction
• What must be done to insoluble compounds for electrolysis?

  They must be melted to make them a molten liquid
• How can soluble compounds be prepared for electrolysis?

  By dissolving them in water
• What equipment is needed for an electrolysis experiment?

  • A beaker full of electrolyte
  • Two electrodes (anode and cathode)
  • A wire connecting the electrodes
  • A power supply
• What is the main difficulty in the electrolysis of aqueous solutions?


  Figuring out which ions will go to each electrode
• What ions are present in aqueous solutions besides those from the ionic compound?

  Hydrogen ions and hydroxide ions from water
• What does the cathode attract during electrolysis?

  The positive ions from the electrolyte
• What is the rule for discharging ions at the cathode?

  The ion of the least reactive element will be discharged
• What happens if the ions of a more reactive metal are present at the cathode?

  The hydrogen ions will be discharged instead of the metal ions
• What is discharged at the anode if a halide is present?

  The halide ions will be discharged
• What happens at the anode if no halide is present?

  The hydroxide ions will be discharged
• What ions are present in an aqueous solution of copper sulfate?

  Copper ions and sulfate ions, along with hydrogen and hydroxide ions from water
• What ions will be discharged at the cathode when copper sulfate is used as the electrolyte?

  The copper ions will be discharged
• What do copper ions gain at the cathode during electrolysis?

  They gain two electrons to form pure copper
• What is produced at the anode when hydroxide ions are discharged?

  Oxygen and water are produced
• What is the equation for the reaction at the anode involving hydroxide ions?

  4 OH⁻ → 2 H₂O + O₂ + 4 e⁻
• What ions are present in an aqueous solution of sodium chloride?

  Sodium ions, chloride ions, hydrogen ions, and hydroxide ions
• Which ions will be discharged at the cathode when sodium chloride is used as the electrolyte?

  The hydrogen ions will be discharged
• What is discharged at the anode when sodium chloride is the electrolyte?

  The chloride ions will be discharged
• What gas is produced at the anode during the electrolysis of sodium chloride?

  Chlorine gas
• What are the key rules for discharging ions during electrolysis?

  • At the cathode: The least reactive ion is discharged.
  • At the anode:
  • If a halide is present, it is discharged.
  • If no halide is present, hydroxide is discharged.