OXIDATION- REDUCTION REACTION REVIEW

Oxidation-Reduction (“Redox”) Reactions Most common reaction Process often written as two “half-reactions”—separating the oxidation and reduction Deals with electron transfer between ionic compounds One compound wants to GIVE electrons, other compound wants to TAKE electrons. Identified by a change in oxidation number

2 chemical processes happening at the same time ! 1) Reduction— GAIN of electrons in element Compound becomes more NEGATIVE DECREASE in oxidation number 2) Oxidation LOSS of electrons Compound becomes more POSITIVE INCREASE in oxidation number

Oxidation and Reduction MUST happen together—can’t have one without the other. electrons gained = electrons lost

Example 1: 2Na + Cl 2  2Na + Cl -

Practice Which equations are reduction half-reactions and which are oxidation half-reactions. 1) Zn e -  Zn 2) Ag  Ag + + e - 3) Cu e -  Cu 4) Al  Al e -

Oxidation Numbers/State Allows us to identify redox reactions A change in these numbers REDOX REACTION ! ! ! Acts like all chemical compounds are ionic----gives atom a charge it would have IF it was ionic

Rule # 1 Examples Br 2 MgCl 2 C 6 H 12 O 6 Cu Ag Fe

Oxidation Number Rules 2) Sum of oxidation numbers for an ion = ion’s charge Examples: SO 4 -2 NH 4 + Al ion Cl ion

Oxidation Number Rules 3) Group 1A metals = +1 Group 2A metals = +2 Examples: MgSO 4 K 3 PO 4

Oxidation Number Rules 4) For the majority of chemical compounds— F = -1 H = +1 (sometimes will have -1) O = -2 Examples: NH 3 H 2 O CO HF KF

Oxidation Number Rules 5) Group 7A Elements = -1 Group 6A Elements = -2 Group 5A Elements = -3 **When combined with a metal in a binary compound !

Rule #5 Examples CaF 2 Li 2 S Mg 3 N K 3 P

Let’s Practice ! Calculate the oxidation number of chromium in each 1) CrO ) Cr 2 O ) CrO 2

More Practice! State which reactions are oxidation-reduction reactions. State which compound is being oxidized and which compound is being reduced. 1) Cu + 2Ag +  Cu Ag 2) CH 3 CO 2 H + OH -  CH 3 CO H 2 O 3) SF 4 + F 2  SF 6 4) CuSO 4 + BaCl 2  BaSO 4 + CuCl 2

Homework Read pp Oxidation-Reduction Review Sheet