4.3.2.2 Writing half-equations for reactions at electrodes

• What does a half-equation represent?

  Changes of ions during electrolysis
• What happens to ions in a half-equation?

  They gain or lose electrons at electrodes
• What is the role of the anode in a half-equation?

  Site where ions lose electrons
• Why is it important to know which ions are present in molten ionic compounds?

  To understand their reactions at anode and cathode
• How do half-equations illustrate the process of electrolysis using sodium chloride?

  • Sodium ions (\(Na^+\)) gain electrons at cathode
  • Chloride ions (\(Cl^-\)) lose electrons at anode
  • Each change is represented by a half-equation
• What happens to chloride ions (\(Cl^-\)) at the anode during electrolysis?

  They lose electrons to become chlorine gas
• What is the role of the cathode in a half-equation?

  Site where ions gain electrons
• What are the ions present in Sodium Chloride and Magnesium Oxide?

  • Sodium Chloride:
  • Anion: Chloride (\(Cl^-\))
  • Cation: Sodium (\(Na^+\))
  • Magnesium Oxide:
  • Anion: Oxide (\(O^{2-}\))
  • Cation: Magnesium (\(Mg^{2+}\))
• What type of ions react at the cathode?

  Cations react at the cathode.
• What are the roles of cations and anions in electrolysis?

  • Cations react at the cathode by gaining electrons.
  • Anions react at the anode by losing electrons.
• What is a half-equation in electrolysis?

  • Represents changes of ions
  • Shows gain or loss of electrons
  • Separate equations for anode and cathode
• What is the cation in Sodium Chloride?

  Sodium (\(Na^+\))
• How do the ions in molten ionic compounds relate to electrolysis?

  They determine reactions at anode and cathode
• What is the charge of the cathode in electrolysis?

  Negative
• Why do negative ions move to the anode?

  Because opposite charges attract
• What are the reactants at the cathode during electrolysis?

  Cations (e.g., \(Na^+\))
• What does the oxidation half-equation at the anode show?

  How anions lose electrons to form neutral atoms
• What are the reactants at the anode during electrolysis?

  Anions (e.g., \(Cl^-\))
• What is the charge of the anode in electrolysis?

  Positive
• What type of ions move to the anode?

  Negative anions like \(Cl^-\)
• What is the anion in Magnesium Oxide?

  Oxide (\(O^{2-}\))
• If you have a different cation, how would you write its reduction half-equation?

  Replace sodium with the new cation
• What happens to chloride ions at the anode during oxidation?

  They lose electrons to form chlorine gas
• What happens to sodium ions (\(Na^+\)) during electrolysis of sodium chloride?

  They gain electrons to become sodium atoms
• What is the reduction half-equation for sodium ions in molten sodium chloride?

  Na⁺ + e^- → Na
• What is the cation in Magnesium Oxide?

  Magnesium (\(Mg^{2+}\))
• What is the relationship between ion charge and electrode attraction in electrolysis?

  • Opposite charges attract
  • Negative ions go to the anode
  • Positive ions go to the cathode
• How do anions react at the anode?

  They lose electrons.
• What ions move to the anode in molten sodium chloride?

  Chloride ions (\(Cl^-\))
• What are the balanced half-equations for the practice problems?

  1. $Zn \rightarrow Zn^{2 + } +$$2e^ -$
  2. $Cl_{2} +$$2e^ - \rightarrow 2Cl^ -$
• What is the first step in writing the oxidation half-equation at the anode?

  Identify the anions moving to the anode
• What are the steps to write a reduction half-equation at the cathode?

  1. Identify the cations
  2. Write the basic equation
  3. Balance the equation
• How is the charge balanced in the iron half-equation?

  By adding one electron to the more positive side
• Why is it important to balance half-equations in redox reactions?

  To ensure that charge is conserved
• What happens to ionic compounds when they are molten?

  They break up into ions
• In the oxidation half-equation, what must be balanced?

  The number of electrons and atoms
• How do you ensure the reduction half-equation is balanced?

  Make sure the number of electrons is balanced
• If sodium ions (\(Na^+\)) are present, where do they react during electrolysis?

  At the cathode.
• What is the purpose of balancing half-equations?

  To ensure charge conservation in redox reactions
• If chloride ions (\(Cl^-\)) are present, where do they react during electrolysis?

  At the anode.