4.3.5.1 Writing balanced half-equations for oxidation and

• How does reduction affect the charge of an atom?

  It becomes more negative
• What is oxidation in chemical reactions?

  Loss of electrons
• What happens to an element's oxidation state if it is reduced?

  It decreases
• In what case does oxygen have an oxidation state of -1?

  In peroxides like H₂O₂
• How can you determine which element is oxidized in a reaction?

  By comparing oxidation states before and after
• What is reduction in chemical reactions?

  Gain of electrons
• What is the oxidation state of copper in the reactant form?

  0
• How do you analyze the oxidation states of elements in a reaction?

  • Compare oxidation states before and after the reaction
  • Identify increases as oxidation
  • Identify decreases as reduction
• What is the oxidation state of copper in its solid form?

  Cu⁰
• What is the oxidation state of copper metal (Cu⁰) before electrolysis?


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• How do you balance the charges in oxidation half-equations?

  Add electrons to the product side
• What happens to copper during electrolysis?

  Copper loses electrons and becomes copper ions
• What is the first step in the reduction half-equation?

  Hydrogen ions gain electrons
• What is the final balanced reduction half-equation?

  2H⁺ + 2e⁻ → H₂
• What is the definition of oxidation in electrolysis?

  Loss of electrons
• What is the first step in balancing oxidation half-equations?

  Identify the element being oxidized
• How do you balance the charge in the reduction half-equation?

  By using 2H⁺ + 2e⁻ → H₂
• What is the definition of reduction in electrolysis?

  Gain of electrons
• What does the sum of oxidation states equal?

  The compound's total charge
• What happens to each hydrogen ion in the reduction half-equation?

  Each gains an electron to form hydrogen gas
• How does oxidation affect the charge of an atom?

  It becomes more positive
• What is the usual oxidation state of oxygen?

  Usually -2
• Why do we add electrons to balance charges in half-equations?

  To ensure total charge is the same
• How do you count the number of atoms for each element in a half-equation?

  Count atoms on both sides of the equation
• How do oxidation and reduction relate to electron transfer in chemical reactions?

  Oxidation involves loss, reduction involves gain
• Why is it important to balance the charge in half-equations?

  To correctly represent electron gain or loss
• What do hydrogen ions become when they gain electrons?

  Hydrogen gas
• How is the oxidation state of simple ions determined?

  It equals the ion's charge
• After balancing the oxygen atoms, how many hydrogen atoms are on the reactant side?

  4 hydrogen atoms
• Why do we use coefficients in balancing half-equations?

  To ensure the number of each atom is equal
• What are the steps to balance charge in a half-equation?

  1. Calculate total charge on both sides
  2. Determine how many electrons to add
  3. Add electrons to the appropriate side
• What are the steps to balance a half-equation?

  1. Identify the elements present.
  2. Count the number of atoms for each element.
  3. Use coefficients to balance the atom counts.
• What are the key terms and their meanings related to oxidation and reduction?

  • Oxidation: Loss of electrons
  • Reduction: Gain of electrons
• In the oxidation of aluminum, what is the half-equation?

  Al → Al³⁺ + 3e⁻
• How do you balance the mass in the reduction half-equation?

  By using 2H⁺ + e⁻ → H₂
• In the reduction of chlorine gas, what is the half-equation?

  Cl₂ + 2e⁻ → 2Cl⁻
• When does hydrogen have an oxidation state of -1?

  When bonded to a metal
• What should you do with terms that appear on both sides of the equation?

  Cancel them out
• How do the oxidation states of copper and oxygen in CuO balance each other?

  Oxygen is -2, copper is +2
• What is the first step to balance mass in a half-equation?

  Identify the elements present in the half-equation