2 Oxidation-Reduction Reactions Reactions that occur when electrons are transferred between atomsAlso called Redox ReactionsOxidation = LOSS of electronsReduction = GAIN of electronsLEO the lion goes GER
3 Oxidation – Reduction Reactions Reaction of sodium metal with chlorine gas:2Na (s) + Cl2 (g) 2NaCl (s)What’s really happening in this reaction?Na ClNa+Cl-Metals ALWAYS lose electrons to nonmetals metals = ox, nonmetals = reducedNa+Cl-Each sodium gives-up an electron to the chlorine resulting in ions!
4 Practice!!In each of the following reactions, identify what is being oxidized, and what is being reduced?2Mg (s) + O2 (g) 2MgO (s)2Al (s) + 3I2 (s) 2AlI3 (s)
5 Can reactions between nonmetals be redox reactions? Yes, but it’s harder to seeCH4 (g) + 2O2 (g) CO2 (g) + H2O (g) + energyUse oxidation states to determine where the electrons are going!
6 Oxidation States Also called oxidation numbers Positive and negative numbers assigned to an INDIVIDUAL atom to help of keep track of electrons during redox reactions
7 Rules for Assigning Oxidation Numbers Oxidation number of a free element = zeroExamples HONClBrIF, solid metals (Na, Ag)Oxidation number of a monatomic ion is the same as it’s chargeExamples NaCl CaCl2Oxygen’s oxidation number in compounds is -2, EXCEPT for peroxides where it is -1Examples O H2O H2O2
8 Rules for Assigning Oxidation Numbers Hydrogen’s oxidation number = +1 in covalent compoundsExamples H2O HI NH3For a neutral compound, the sum of the oxidation states must be ZEROExamples CuCl2 Fe2O3For polyatomic ions, the sum of the oxidation numbers must equal the charge of the ionExamples SO42-
9 Practice!! Assign oxidation numbers to each of the following atoms: SO3 N2O5 C2H6SO32- PF3
10 What do we use oxidation numbers for? To determine what is being oxidized and what is being reduced in a redox reactionExample:Identify what is oxidized and reduced in the following reaction:HINT Oxidation = INCREASE in oxidation #Reduction = DECREASE in oxidation #CH4 (g) + 2O2 (g) CO2 (g) + H2O (g)
11 Practice!!Determine what is oxidized and reduced in the following reactions:Cu (s) + 2AgNO3 (aq) Cu(NO3)2 + 2AgBr2 (g) + 2NaF (aq) 2NaBr (aq) + F2 (g)CH3OH (g) + O2 (g) CO2 (g) + H2O (g)
12 Two more terms to know… Reducing Agent electron donor What is oxidized in the reactionOxidizing Agent electron acceptorWhat is reduced in the reactionIdentify the reducing agent and oxidizing agent in the previous 3 reactions:Cu (s) + 2AgNO3 (aq) Cu(NO3)2 + 2AgBr2 (g) + 2NaF (aq) 2NaBr (aq) + F2 (g)CH3OH (g) + O2 (g) CO2 (g) + H2O (g)