Oxidation-Reduction Topic 9 Review Book

Oxidation Numbers Oxidation is the loss of electrons; Reduction is the gain of electrons Oxidation and reduction go together. Whenever a substance loses electrons and another substance gains electrons Oxidation Numbers are a system that we can use to keep track of electron transfers

GER! LEO says Loss of Electrons = Oxidation Gain of Electrons = Reduction

Rules for Assigning Oxidation Numbers Free elements are 0 Ions have the charge indicated Metals : Group 1 = +1; Group 2= +2 Halogens in binary compounds are usually -1, in ternary compounds move on and go back to do the algebra Hydrogen is +1 unless in binary compound with metal, then it is -1 Oxygen is -2 unless in peroxide when it is -1 or with fluorine when it is +2 (FIMHHO)

Practice Assigning Oxidation Numbers NO2 N2O5 HClO3 HNO3 Ca(NO3)2 KMnO4

Practice Assigning Oxidation Numbers NO2 N= +4, O = -2 N2O5 N = +5, O = -2 HClO3 H=+1, Cl=+5, O = -2 HNO3 H=+1, N = +5, O = -2 Ca(NO3)2 Ca=+2, N =+5, O= -2 KMnO4 K=+1, Mn=+7, O= -2

Practice Assigning Oxidation Numbers CaCl2 K2Cr2O7 KH NaHCO3 H2O MgO

Practice Assigning Oxidation Numbers CaCl2 Ca = +2, Cl = -1 K2Cr2O7 K=+1, Cr=+6, O=-2 KH K = +1, H= -1 NaHCO3 Na= +1, H= +1, C=+4, O= -2 H2O H= +1, O= -2 MgO Mg = +2, O = -2

Using Oxidation Numbers Careful examination of the oxidation numbers of atoms in an equation allows us to determine what is oxidized and what is reduced in an oxidation-reduction reaction

Using Oxidation Numbers An increase in the oxidation number indicates that an atom has lost electrons and therefore oxidized. A decrease in the oxidation number indicates that an atom has gained electrons and therefore reduced Example Mg + ZnSO4  MgSO4 + Zn

Exercise Cl2 + KBr  KCl + Br2 Mg + HNO3  Mg(NO3)2 + NO2 + H2O For each of the following reactions find the element oxidized and the element reduced Cl2 + KBr  KCl + Br2   Mg + HNO3  Mg(NO3)2 + NO2 + H2O HNO3 + I2  HIO3 + NO2

Exercise Cl2 + KBr  KCl + Br2 Br increases from –1 to 0 -- oxidized For each of the following reactions find the element oxidized and the element reduced Cl2 + KBr  KCl + Br2 Br increases from –1 to 0 -- oxidized Cl decreases from 0 to –1 -- Reduced K remains unchanged at +1

Exercise Mg increases from 0 to +2. It is oxidized For each of the following reactions find the element oxidized and the element reduced Mg + HNO3  Mg(NO3)2 + NO2 + H2O Mg increases from 0 to +2. It is oxidized Only N in nitric acid changes from +5 to +4. It is reduced

Exercise HNO3 + I2  HIO3 + NO2 For each of the following reactions find the element oxidized and the element reduced HNO3 + I2  HIO3 + NO2 N is reduced from +5 to +4. It is reduced I is increased from 0 to +5 It is oxidized The hydrogen and oxygen remain unchanged.

Balancing Redox Reactions There are several basic steps Assign oxidation numbers to the species in the reaction Find the substance oxidized and the substance reduced Write half reactions for the oxidation and reduction Balance the atoms that change in the half reaction Determine the electrons transferred and balance the electrons between the half reactions Check your work. Make sure that both the atoms and charges balance

Balancing Redox Equations 1 Assign oxidation numbers to the species in the reaction Find the substance oxidized and the substance reduced Write half reactions for the oxidation and reduction Balance the atoms that change in the half reaction Determine the electrons transferred and balance the electrons between the half reactions Check your work. Make sure that both the atoms and charges balance *It may be helpful to balance the equation before starting the redox process Zn + HCl  ZnCl2 + H2

Balancing Redox Equations 2 Assign oxidation numbers to the species in the reaction Find the substance oxidized and the substance reduced Write half reactions for the oxidation and reduction Balance the atoms that change in the half reaction Determine the electrons transferred and balance the electrons between the half reactions Check your work. Make sure that both the atoms and charges balance MnO2 + HCl  MnCl2 + Cl2 + H2O

Balance, Assign, ID, write ½ rxns for the following 1. Mg + O2  MgO 2. KClO3  KCl + O2 3. HCl + O2  H2O + Cl2

Balance the following ionic equations ____Cr +6 + ____ S  ___ Cr +3 +____ S +4 ____Sn2+ + ____Hg+ 2  ___Sn+4 + ___Hg +1 _____Cu + _____Ag+1  ___Cu+2 + ___Ag