Redox Reactions short notes

Oxidation and reduction

• Oxidation is loss of electrons, and reduction is gain. An oxidising agent gets reduced, and a reducing agent gets oxidised.

Oxidation number rules

• Free elements are 0.
• Monatomic ions equal their charge.
• Oxygen is usually −2, but −1 in peroxides, −½ in superoxides, and +2 in OF₂.
• Hydrogen is usually +1, but −1 in metal hydrides such as NaH.
• Fluorine is always −1.
• The numbers in a neutral compound add to 0, and in an ion they add to its charge.

Types of reaction

• Combination, decomposition and displacement reactions can all be redox.
• Disproportionation: one element is both oxidised and reduced, as when H₂O₂ gives H₂O and O₂.

Balancing

• Oxidation number method: find the change in numbers, then equalise it.
• Half-reaction method: balance each half separately, with electrons, then add them.
• In acid, balance O with H₂O and H with H⁺.
• In base, add OH⁻ to both sides to remove H⁺.

Equivalents

n-factor in titration

$\displaystyle N_1V_1 = N_2V_2$

Normality is molarity × n-factor.