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Oxidation-Reduction Topic 9 Review Book.

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Presentation on theme: "Oxidation-Reduction Topic 9 Review Book."— Presentation transcript:

1 Oxidation-Reduction Topic 9 Review Book

2 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

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

4 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)

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

6 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

7 Practice Assigning Oxidation Numbers
CaCl2 K2Cr2O7 KH NaHCO3 H2O MgO

8 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

9 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

10 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

11 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 Cl KBr  KCl Br2 Mg HNO3  Mg(NO3) NO2 + H2O HNO I  HIO NO2

12 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 Cl KBr  KCl Br2 Br increases from –1 to oxidized Cl decreases from 0 to – Reduced K remains unchanged at +1

13 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) NO2 + H2O Mg increases from 0 to It is oxidized Only N in nitric acid changes from +5 to +4. It is reduced

14 Exercise HNO3 + I2  HIO3 + NO2
For each of the following reactions find the element oxidized and the element reduced HNO I  HIO 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.

15 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

16 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

17 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

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

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


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