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
• 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 like most metal oxides for electrolysis?

  They must be melted to make them a molten liquid
• How can soluble compounds like copper sulfate 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 joining 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
• Which ions does the negative cathode attract?

  The positive ions from the compound and hydrogen ions from water
• What determines which ion is discharged at the cathode?

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

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

  Negative ions from the compound and hydroxide ions can be discharged
• What is the rule for discharging ions at the anode when halides are present?

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

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

  Copper 2 plus ions and sulfate 2 minus ions
• What happens at the cathode when copper sulfate is electrolyzed?

  Copper ions gain electrons and form pure copper
• What is the result of the discharge of hydroxide ions at the anode during copper sulfate electrolysis?

  They 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, and hydroxide ions
• Which ions will be discharged at the cathode during the electrolysis of sodium chloride?

  The hydrogen ions will be discharged
• What happens at the anode during the electrolysis of sodium chloride?

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

  Chlorine gas
• What are the key rules for determining which ions are discharged during electrolysis?

  • At the cathode, the least reactive positive ion is discharged.
  • At the anode, if halides are present, they are discharged; otherwise, hydroxide ions are discharged.