Electrolysis Part 3 - Aqueous Solutions

• 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
• What does the cathode attract?

  Positive ions from the electrolyte
• What determines which ion is discharged at the cathode?

  The ion of the least reactive element
• 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 electrolysis of copper sulfate?

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

  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
• Which ions will be discharged at the cathode during sodium chloride electrolysis?

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

  Chloride ions lose electrons to form chlorine gas
• What gas is formed at the cathode during sodium chloride electrolysis?

  Hydrogen gas
• What gas is formed at the anode during sodium chloride electrolysis?

  Chlorine gas
• What are the key steps in the electrolysis process for copper sulfate and sodium chloride?

  1. Identify ions in the solution
  2. Determine which ions discharge at the cathode
  3. Determine which ions discharge at the anode
  4. Observe the products formed at each electrode