Displacement reactions recombine ions Acid-Base reactions H+ transfer Fe2O3 (s) + Al (s)  Al2O3 (s) + Fe (l) thermite reaction Oxidation-Reduction reactions (redox) e- transfer Fe2O3 = iron ( ) III oxide Fe3+ Fe (l) = Fe0 Fe3+ has_____ protons 26 Fe0 has _____ protons 26 Fe3+ has ____ electrons 23 Fe0 has ____ electrons 26 Fe3+ gained 3 electrons gaining e- = reduction reducing the oxidation state 3+ 

Fe2O3 (s) + Al (s)  Al2O3 (s) + Fe (l) Al (s) = Al0 Al2O3 aluminum oxide Al0 has _____ electrons 13 Al3+has ______ electrons 10 oxidation state = oxidation state = 3+ Al0 loses___ e- 3 losing e- = oxidation increase oxidation number  3+ LEO GER Lose Electrons Oxidation Gain Electrons Reduction

Rules for oxidation numbers 1. Oxidation number for elements is zero. N2, O2, Na(s), Co(s), He (g) Oxidation number of monatomic ions is the same as their charge Group IA = +1 Al3+, Zn2+, Cd2+, Ag+ Group IIA = +2 Oxidation number of oxygen in most compounds is –2. Exceptions: H2O2, O2- (peroxides) –1 4. Oxidation number of hydrogen is +1 Exceptions: bonded to metals LiH 5. Fluorine is always –1. Other halogens are –1. Exceptions: bonded to O, they are positive

Assign oxidation numbers to all of the elements: Li2O Li = +1 O = -2 PF3 P = +3 F = -1 HNO3 H = +1 N = +5 O = -2 MnO4- Mn = +7 O = -2 Cr2O72- Cr = +6 O = -2

What is the oxidation state of the highlighted element? P2O5 +5 diphosphorous pentoxide NaH -1 sodium hydride SnBr4 +4 tin (IV) bromide BaO2 -1 barium peroxide

Redox reactions +1 +2 Zn (s) + 2H+ (aq)  H2 (g) + Zn 2+ Zn  +2 increase oxidation state lose electrons oxidized reducing agent H +1  decrease oxidation state gain electrons reduced oxidizing agent

+1 -2 2H2(g) + O2 (g)  2H2O(l) H loses or gains electrons is oxidized or reduced oxidizing or reducing agent O loses or gains electrons is oxidized or reduced oxidizing or reducing agent

+7 +3 +4 2H2O + Al(s) + MnO4-  Al(OH)4- + MnO2 H2O What is being oxidized? Al What is oxidation? MnO4- LEO Al(OH)4- MnO2 How many e-? What is being reduced? GER What is the reducing agent?

What is the oxidation state of S in each of these compounds: H2S S = -2 H = +1 S8 S = SCl2 S = +2 Cl = -1 Na2SO3 S = +4 O = -2 Na = +1 SO42- S = +6 O = -2 Which of these compounds can not act as a reducing agent? Which of these compounds can not act as a oxidizing agent?

+4 -2 +1 -2 +2 -2 +1 +2 -2 +1 Cd(s) + NiO2 + 2H2O  Cd(OH)2 + Ni(OH)2 What is being oxidized? What is being reduced? What is the oxidizing agent? What is the reducing agent? How many electrons are transferred?