Electrolysis Part 3

• What is electrolysis used for?

  To split compounds into their elements
• How does electrolysis work?

  By passing an electric current through an electrolyte
• What must happen for electrolysis to work?

  Ions in the electrolyte must be free to move
• What must be done to insoluble compounds for electrolysis?

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

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

  • Beaker full of electrolyte
  • Two electrodes (anode and cathode)
  • Wire connecting electrodes
  • Power supply
• What is the main difficulty in electrolysis of aqueous solutions?

  Determining which ions go to each electrode
• What ions are present in aqueous solutions besides the ionic compound ions?

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

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

  The least reactive ion will be discharged
• What happens if copper ions are present at the cathode?

  Copper ions will be discharged instead of hydrogen
• What is discharged at the anode if halides are present?

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

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

  Copper 2+ and sulfate 2- ions
• What happens at the cathode during the electrolysis of copper sulfate?

  Copper ions gain electrons and form solid copper
• What is the reaction at the anode during the electrolysis of copper sulfate?

  Hydroxide ions form oxygen and water
• What is the equation for the reaction of hydroxide ions at the anode?

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

  Sodium ions, chloride ions, hydrogen ions, hydroxide ions
• What happens at the cathode during the electrolysis of sodium chloride?

  Hydrogen ions are discharged to form hydrogen gas
• What happens at the anode during the electrolysis of sodium chloride?

  Chloride ions are discharged to form chlorine gas
• What are the key rules for discharging ions during electrolysis?

  • At the cathode: least reactive ion discharges
  • At the anode: halide ions discharge if present; otherwise, hydroxide discharges