Better known as REDOX Lesson 1 Reduction/Oxidation Better known as REDOX Lesson 1

Oxidation and Reduction Oxidation is the loss of electrons during a reaction (increase in charge). Reduction is the gain of electrons during a reaction (decrease in charge). LEO the lion says GER OIL RIG (Oxidation Is Losing electrons, Reduction Is Gaining electrons) Oxidation and reduction must always happen together. In a reaction one element is oxidized and another element is reduced.

Types of Redox Reactions Synthesis and decomposition are all redox reactions. Single replacement reactions will be redox if they happen. Elements becoming compounds or compounds becoming elements always involve a change in oxidation number.

Oxidation Numbers (Ion Charge) Elements not in compounds are always 0. Hydrogen is +1. Group 1 elements are +1. Group 2 elements are +2. Aluminum is +3. Halogens are -1 (unless in polyatomic ion). Oxygen is -2 (except in peroxide where it is -1). The oxidation numbers of other elements can be figured using the above known ones.

Sample Problem What is the oxidation number of each element in the following compounds: (a) Al2O3 (b) Mg (c) NaClO3 (d) Ca(NO3)2 (a) Al= +3, O= -2 (b) Mg= 0 (c) Na= +1, Cl= +5, O= -2 (d) Ca= +2, N= +5, O= -2

Sample Problem Assign oxidation numbers to each element and identify the element that is oxidized and the element that is reduced in the following reaction: +1 -2 +1 +5 -2 0 +2 -2 +1 -2 3 H2S + 2 HNO3  3 S + 2 NO + 4 H2O Oxidized: S Reduced: N

Redox Agents The element oxidized is the reducing agent. Common reducing agents are Na, K, Mg, Al, Zn, and Fe The element reduced is the oxidizing agent. Strong oxidizing agents usually contain F, O, or Cl

Practice—Assign Oxidation Numbers As + NaOH ---> Na3AsO3 + H2 0 +1 -2+1 +1 +3 -2 0 C8H16 + Cl2 ---> C + HCl -2 +1 0 0 +1 -1 Xe + F2 ---> XeF6 0 0 +6 -1

Gummy Bear Explosion— Assign Oxidation Numbers What is Oxidized Gummy Bear Explosion— Assign Oxidation Numbers What is Oxidized? What is Reduced? KClO3 + C12H22O11 → H2O + CO2 + KCl 2KClO3 → 2KCl + 3O2 C12H22O11 + O2 → 9C + 3CO2 + H2O +1+5-2 0 +1 -2 +1 -2 +4 -2 +1 -1 +1+5-2 +1-1 0 0 +1 -2 0 0 +4-2 +1 -2 Oxidized: C, O Reduced: Cl, O