3.2.1 Balancing Redox Equations

• What is the mnemonic for remembering oxidation and reduction in terms of electron transfer?

  OIL RIG
• The oxidation half-equation for iron is $Fe → Fe²⁺ +$$2e⁻$
• Match the process with its electron change and example:

  Oxidation ↔️ Loss; $Fe → Fe^{2 + } +$$2e^ -$

  Reduction ↔️ Gain; $Cu^{2 + } +$$2e^ - → Cu$
• In the reaction between iron and copper(II) ions, iron is oxidized and copper(II) ions are reduced.
• Monoatomic ions have an oxidation state equal to their charge
• What is the oxidation state of oxygen in most compounds?

  -2
• In $H₂O$, hydrogen has an oxidation state of +1 and oxygen has -2.
• Steps to write half-equations

  1️⃣ Identify oxidation and reduction

  2️⃣ Write each process as a separate equation

  3️⃣ Balance atoms and charge by adding electrons
• Match the process with its half-equation:

  Oxidation ↔️ $Zn → Zn^{2 + } +$$2e^ -$

  Reduction ↔️ $Cu^{2 + } +$$2e^ - → Cu$
• What is the usual oxidation state of oxygen except in peroxides and fluorides?

  -2
• Half-equations represent either the oxidation or reduction process in a redox reaction separately
• Write the half-equation for the oxidation process of iron.

  $Fe → Fe²⁺ +$$2e⁻$
• Write the half-equation for the reduction process of copper(II) ions.

  $Cu²⁺ +$$2e⁻ → Cu$
• Half-equations represent either the oxidation or reduction process in a redox reaction separately.
• To balance the number of atoms and charge in a half-equation, add electrons
• What is the first step in balancing atoms other than oxygen and hydrogen in a half-equation?

  Identify the atoms
• To balance oxygen atoms in a half-equation, add water
• Oxidation involves the loss of electrons.
• The mnemonic 'OIL RIG' stands for Oxidation Is Loss, Reduction Is Gain
• What is the oxidation state of a free element?

  0
• The sum of oxidation states in a neutral compound is always 0.
• What is the typical oxidation state of oxygen in a compound?

  -2
• What is the typical oxidation state of hydrogen in a compound?

  +1
• Half-equations represent either the oxidation or reduction part of a redox reaction separately.
• Write the oxidation half-equation for zinc.

  $Zn → Zn^{2 + } +$$2e^ -$
• Write the reduction half-equation for copper(II) ions.

  $Cu^{2 + } +$$2e^ - → Cu$
• Balancing atoms other than oxygen and hydrogen involves multiplying compounds by coefficients.
• To balance atoms other than oxygen and hydrogen, multiply the appropriate compounds or ions by coefficients
• What is added to balance oxygen atoms in a half-equation?

  $H_{2}O$
• What is the first step to balance oxygen atoms in a half-equation?

  Identify fewer oxygen atoms
• To balance oxygen atoms, add water molecules ($H_{2}O$) to the side with fewer oxygen atoms
• Oxygen atoms are balanced by adding water molecules to the side with more oxygen atoms

  False
• How many water molecules are added to balance the oxygen atoms in the half-equation $MnO_{4}^{ - } → Mn^{2 + }$?


  4
• To balance the half-equation $MnO_{4}^{ - } → Mn^{2 + }$, we add 4 water molecules to the product
• Hydrogen atoms are balanced by adding hydrogen ions ($H⁺$) to the side with fewer hydrogen atoms
• In the half-equation MnO_{4}^{ - } → Mn^{2 + } + 4H_{2}O</latex>, how many hydrogen ions are needed to balance the hydrogen atoms?

  8
• The balanced half-equation for hydrogen atoms is $MnO_{4}^{ - } +$$8H⁺ → Mn^{2 + } +$$4H_{2}O$ where $8H⁺$ balances the hydrogen
• To balance charges in a half-equation, add electrons to the side with the more positive charge
• In the half-equation MnO_{4}^{ - } + 8H⁺ → Mn^{2 + } + 4H_{2}O</latex>, what is the total charge on the reactant side?

  +7
• To balance the charges in the half-equation $MnO_{4}^{ - } +$$8H⁺ → Mn^{2 + } +$$4H_{2}O$, we add 5 electrons to the reactant