4.9 Electrolysis 3 - 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
• What must happen to ions in an electrolyte for electrolysis to work?

  The ions must be free to move around
• What must be done to insoluble compounds for electrolysis?

  They must be melted to form 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 (positive anode and negative cathode)
  • A wire connecting the electrodes
  • A power supply
• What is the main difficulty in the electrolysis of aqueous solutions?

  Determining 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 cathode attracts positive ions
• What is the rule for discharging ions at the cathode?

  The ion of the least reactive element will be discharged
• If copper ions are present, which ions will be discharged at the cathode?

  Copper ions will be discharged
• What happens at the anode during electrolysis?

  Negative ions can be discharged
• What is the rule for discharging ions at the anode?

  If a halide is present, it will be discharged; otherwise, hydroxide is discharged
• What ions are present in an aqueous solution of copper sulfate?

  Copper 2+ ions and sulfate 2- ions
• What will happen at the cathode when copper sulfate is electrolyzed?

  Copper ions will gain electrons and form pure copper
• What is produced at the anode when copper sulfate is electrolyzed?

  Oxygen and water are produced
• What is the equation for the reaction at the anode during the electrolysis of copper sulfate?

  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 during the electrolysis of sodium chloride?

  Hydrogen ions will be discharged
• What will happen at the anode during the electrolysis of sodium chloride?

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

  Chlorine gas is produced