Redox Reactions Many practical or everyday examples of redox reactions: Corrosion of iron (rust formation) Forest fire Charcoal grill Natural gas burning Batteries Metabolic processes combustion

CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (g) Redox Reactions There are many different kinds of redox reactions. Combustion CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (g) Oxidation of Metals by Acids or Metal Salts Cu (s) + H2SO4 (aq)  CuSO4 (aq) + H2 (g)

Redox Reactions Oxidation of Metals by Acids or Metal Salts The reaction between a metal and an acid or between a metal and a metal salt is called a displacement reaction. a reaction in which an element reacts with a compound and displaces an element from that compound A + BX  AX + B

Redox Reactions Oxidation of Metals by Acids or Metal Salts Examples: Mg (s) + 2HCl (aq)  MgCl2 (aq) + H2 (g) Zn (s) + 2 HBr (aq)  ZnBr2 (aq) + H2 (g) Mn (s) + Pb(NO3)2 (aq)  Mn(NO3)2 (aq) + Pb (s)

Redox Reactions Oxidation of Metals by Acids or Metal Salts How do you know if a redox reaction has occurred? You must examine the oxidation number of each of the elements present in the reactants and products. If the oxidation number changes, then a redox reaction has occurred.

Redox Reactions Oxidation of Metals by Acids or Metal Salts When oxidation occurs: Electrons are lost Oxidation number increases When reduction occurs: Electrons are gained Oxidation number is reduced (decreases)

Redox Reactions Oxidation of Metals by Acids or Metal Salts Mg(s) + 2HCl (aq)  MgCl2 (aq) + H2 (g) -1 +2 +1 Oxidation # of Mg increased oxidation Oxidation # of H+ ion reduced reduction

Redox Reactions Oxidation of Metals by Acids or Metal Salts Example: Identify the element that has been oxidized and the one that has been reduced. Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2 (g)

Redox Reactions Oxidation of Metals by Acids or Metal Salts To determine which components have been oxidized and reduced, find the oxidation numbers: Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2 (g) oxidized reduced +1 -1 +2

Redox Reactions Oxidation of Metals by Acids or Metal Salts You can also write a net ionic equation to describe the reaction: Write all soluble strong electrolytes as ions Eliminate the spectator ions Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2 (g) Zn (s) + 2 H+ (aq) + 2 Cl- (aq)  Zn2+ (aq) + 2 Cl- (aq) + H2 (g) Zn (s) + 2H+ (aq)  Zn2+ (aq) + H2 (g)

Redox Reactions Oxidation of Metals by Acids or Metal Salts Example: Write the complete ionic and net ionic equations for the reaction. Which element is oxidized? 2 Al (s) + 3 Ni(NO3)2 (aq)  2 Al(NO3)3 (aq) + 3 Ni (s) 2 Al (s) + 3 Ni2+(aq) + 6 NO3- (aq)  2 Al3+ (aq) + 6 NO3- (aq) + 3 Ni (s) 2 Al (s) + 3 Ni 2+(aq)  2 Al3+ (aq) + 3 Ni (s)

Redox Reactions Oxidation of Metals by Acids or Metal Salts +5 +5 2 Al (s) + 3 Ni(NO3)2 (aq) 2 Al(NO3)3 (aq) + 3 Ni (s) oxidized -2 -2 +3 +2

Redox Reactions Oxidation of Metals by Acids or Metal Salts Based on the previous equation, we wouldn’t want to store a solution of Ni(NO3)3 in an aluminum container. The aluminum container would react and dissolve!!! Metals differ in the ease with which they are oxidized. Al (s) is oxidized by Ni(NO3)3 (aq) Ag(s) is NOT oxidized by Ni(NO3)3 (aq)

Redox Reactions Oxidation of Metals by Acids or Metal Salts Activity series: A list of metals arranged in order of decreasing ease of oxidation Used to predict whether a metal will react with an acid or with a metal salt See table 4.5

Activity Series