4.3 Electrolysis

• What is represented by the symbol 'e-' in half equations?

  Electrons
• What does the small number in a half equation represent?

  It is always the same as the two larger numbers within the equation
• What are the half equations for reactions at each electrode?

  • Negative electrode: \( X^+ + e^- \rightarrow X \) (electrons gained, positive ions reduced)
  • Positive electrode: \( X^- \rightarrow e^- + X \) (electrons lost, negative ions oxidized)
• What happens to ions when an ionic substance is melted or dissolved?

  The ions are free to move about within the liquid or solution
• What is the process called when a current is passed through molten or dissolved substances?

  Electrolysis
• What is the substance being broken down during electrolysis called?

  Electrolyte
• Which electrode do positively charged ions move to during electrolysis?

  Negative electrode (cathode)
• Which electrode do negatively charged ions move to during electrolysis?

  Positive electrode (anode)
• What is produced at the cathode during the electrolysis of molten ionic compounds?

  The metal
• What is produced at the anode during the electrolysis of molten ionic compounds?

  The non-metal
• Why is aluminium extracted by electrolysis instead of reduction with carbon?

  Because aluminium is more reactive than carbon
• What is required to extract metals by electrolysis?

  Large amounts of energy to melt the compounds and produce electrical current
• What is the mixture used in the electrolysis of aluminium oxide?

  Aluminium oxide and cryolite
• Why is cryolite mixed with aluminium oxide during electrolysis?

  To lower the melting point of aluminium oxide
• Why do positive electrodes need to be continually replaced during aluminium extraction?

  Because oxygen formed reacts with carbon, producing carbon dioxide
• What can metals that react with carbon be extracted by?

  Electrolysis
• What determines the ions discharged during the electrolysis of aqueous solutions?

  The relative reactivity of the elements involved
• What is produced at the cathode during the electrolysis of an aqueous solution?

  Hydrogen, unless the metal is less reactive than hydrogen
• What is produced at the positive electrode if OH- and halide ions are present during electrolysis?

  One of the halide ions
• What is produced at the positive electrode if no halide is present during electrolysis?

  Oxygen
• What happens to water molecules in an aqueous solution during electrolysis?

  They break down producing H+ ions and OH- ions
• How does the electrolysis of molten ionic compounds differ from that of aqueous solutions?

  In molten compounds, ions are free to move, while in aqueous solutions, water molecules also break down