Oxidation Number Practice MgCl2 Mg(NO3)2 Al2(SO4)3 Ba(NO3)2 FeCl3 OF2 H2O2 Al2S3 Fe O2 Work from outside in, start with O or F if possible More examples: FePO4 P2O5 N2O4 CO2

Redox Equations Identify what is being oxidized and what is being reduced (LEO goes GER) Reducing agent – causes reduction (is oxidized) Oxidizing agent – causes oxidation (is reduced) Draw arrows from element in reactants to products, write the charge and determine if it has gained or lost electrons

Redox Example 1 CH4 + 2O2 → CO2 + 2H2O Write in ox numbers and arrows C-4 is oxidized O20 is reduced

Redox Example 2 Cr2O72- + OH- → 2CrO42- + H2O Not redox because ox numbers don't change

Redox Example 3 2H2O2 → 2H2O + O2 H2O2 is ox agent and reducing agent O from peroxide is reduced to O in water and oxidized to O in O2

Redox Practice

Activity Series Used to determine the products of a single replacement reaction An element higher in the series will replace a lower element in a compound Zn(s) + CuCl2(aq) → ZnCl2(aq) + Cu Determine what is oxidized and what is reduced What conclusion can you make about oxidation and replacement? Higher the element, the easier it will be oxidized

Writing Half Reactions CH4 + 2O2 → CO2 + 2H2O oxidation: CH4 → CO2 reduction: 2O2 → 2H2O Zn + 2HCl → ZnCl2 + H2 ox: Zn → Zn+2 + 2e- red: 2e- + 2H+ → H2 overall: Zn + 2H+ → Zn+2 + H2

Balancing Redox by Half Reaction Method 1. write half reaction for oxidation reduction Do not include polyatomic ions that do not change 2. For each half reaction: Balance all elements except H and O Balance O by adding H2O Balance H by adding H+ Balance charge using electrons 3 if necessary, multiply one or both of the balanced half reactions to equalize the number of electrons in the 2 half reactions 4. add half reactions – cancel identical species on opposite sides of the arrow 5. check elements and charges are balanced