Electrolysis

• 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 of electrolysis?

  Electrolysis is the breakdown of a substance into elements by passing a current through it.
• What is the substance being broken down during electrolysis called?

  The substance is called the electrolyte.
• Which ions move to the cathode during electrolysis?

  Positively charged ions move to the negative electrode (cathode).
• Which ions move to the anode during electrolysis?

  Negatively charged ions move to the positive electrode (anode).
• What is produced at the cathode during the electrolysis of molten lead bromide?

  Lead is produced at the cathode.
• What is produced at the anode during the electrolysis of molten lead bromide?

  Bromine is produced at the anode.
• Why is lead produced at the cathode during the electrolysis of lead bromide?

  Because lead is the positive ion and bromine is the negative ion.
• How are metals that are more reactive than carbon extracted?

  They are extracted by electrolysis of molten compounds.
• What is a significant drawback of the electrolysis extraction process?

  Large amounts of energy are used in the extraction process.
• What is the role of cryolite in the electrolysis of aluminium oxide?

  Cryolite is mixed with aluminium oxide to lower its melting point.
• Why do positive electrodes need to be continually replaced during the electrolysis of aluminium?

  Because oxygen is formed, which reacts with the carbon of the positive electrodes, forming carbon dioxide.
• What type of metals can be extracted by electrolysis?

  Metals that react with carbon can be extracted by electrolysis.
• What determines the ions discharged during the electrolysis of an aqueous solution?

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

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

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

  Oxygen is formed.
• What happens to water molecules during electrolysis of an aqueous solution?

  Water molecules break down producing H+ ions and OH- ions.
• What is represented by the symbol ‘e-‘ in half equations?

  Electrons are represented by the symbol ‘e-‘.
• What are the half equations for reactions at the electrodes during electrolysis?

  • Negative electrode: \( X^+ + e^- \rightarrow X \) (positive ions are reduced)
  • Positive electrode: \( X^- \rightarrow e^- + X \) (negative ions are oxidised)