Introduction to Oxidation-Reduction Reactions

Overview

Oxidation-reduction (redox) reactions are fundamental chemical processes in which electrons are transferred between substances. These reactions are essential in both biological and industrial contexts, including energy production, metabolism, and chemical manufacturing.

• Oxidation: Loss of electrons by a substance.

• Reduction: Gain of electrons by a substance.

• Redox reactions always involve both oxidation and reduction occurring simultaneously.

Properties and Uses of Sodium and Chlorine

Sodium (Na)

• Type: Metal

• Occurrence: Does not occur naturally as elemental sodium () due to its high reactivity.

• Reactivity: Reacts violently with water, forming sodium hydroxide and hydrogen gas.

• Applications: Used as a coolant in some nuclear reactors.

Chlorine ()

• Type: Nonmetal

• Uses: Employed as a bleach and disinfectant.

• Oxidizing Power: Powerful oxidant.

• Historical Use: Used as a chemical weapon in WWI (Germany), Iraq War (insurgents), and Syria.

Formation of Sodium Chloride

Ionic Compound Structure

Sodium chloride () is formed when sodium and chlorine react, resulting in a crystalline ionic lattice. Sodium donates an electron to chlorine, forming and ions.

• Example: Table salt is a common form of sodium chloride.

Oxidation and Reduction Half-Reactions

Na + Cl2 Reaction

When sodium reacts with chlorine, the process can be split into two half-reactions:

• Oxidation (Sodium):

• Reduction (Chlorine):

Identifying Oxidized and Reduced Species

Example Reaction

• Oxidized: Copper () loses electrons and is converted to .

• Reduced: Silver ion () gains electrons and is converted to metallic silver ().

• Oxidant (Oxidizing Agent): Silver ion () – causes oxidation of copper.

• Reductant (Reducing Agent): Copper () – causes reduction of silver ion.

Balancing Redox Reactions

General Approach

Redox reactions must be balanced for both mass and charge. This often involves identifying oxidation states and ensuring electron transfer is equal on both sides.

• Example:

• Balance atoms and charges by adjusting coefficients and adding electrons as needed.

Examples of Redox Reactions

Combustion and Decomposition

• Combustion of Octane:

• Electrolysis of Water:

• Decomposition of Organic Compounds:

• Glucose Oxidation:

Oxidation Numbers

Definition and Rules

Oxidation numbers (states) are assigned to atoms to track electron transfer in redox reactions. They help identify which atoms are oxidized or reduced.

• Element: Oxidation number = 0

• Monatomic Ion: Oxidation number = ion charge

• Sum of Oxidation Numbers: For a neutral compound, sum = 0; for a polyatomic ion, sum = ion charge

• Assignment in Compounds:

  • Determine number of valence electrons from the periodic table.

  • Consider each bond as fully ionic.

  • Assign all bonding electrons to the more electronegative atom.

  • Oxidation number = (# valence electrons) – (# electrons assigned in the structure)

Common Oxidation Numbers in Compounds

Examples

Determining Oxidation Number of Chlorine in

Calculation

• Let x = oxidation number of Cl.

• Each O = -2; three O atoms:

• Sum of oxidation numbers = charge on ion:

• Solve:

Additional Redox Examples

Organic Compounds

• Methane (): C: -4, H: +1

• Methanol (): C: -2, H: +1, O: -2

• Formaldehyde (): C: 0, H: +1, O: -2

• Formic acid (): C: +2, H: +1, O: -2

Glucose Oxidation

Fatty Acid Example

• Long-chain carboxylate shown as an example of organic redox chemistry.

Additional info: The notes include images of sodium metal, chlorine gas, and crystal structures to illustrate the physical forms and properties of reactants and products in redox reactions.