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Chapters 3 and 4

Chemical Reactions
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Chemical Reactions
  • Chemical reactions are processes in which one set of chemicals are converted to a new set of chemicals
  • Chemical reactions are described by chemical equations.
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Chemical Equations
  • 2 C8H18(l) + 25 O2 (g) ®16 CO2 (g) +18 H2O(g)


  • must be balanced to satisfy Law of conservation of mass
  • state designations
    • (g) gas
    • (l) liquid
    • (s) solid
    • (aq) aqueous
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Pure silicon, which is needed in the manufacturing of electronic components, may be prepared by heating silicon dioxide (sand) with carbon at high temperatures, releasing carbon monoxide gas.  Write the balanced chemical equation for this process.
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Carbon tetrachloride was widely used for many years as a solvent until its harmful properties became well established.  Carbon tetrachloride may be prepared by the reaction of natural gas (methane, CH4) and elemental chlorine gas in the presence of ultraviolet light.  Write a balanced chemical equation for this process.
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"Crude gunpowders often contain a..."
  • Crude gunpowders often contain a mixture of potassium nitrate and charcoal (carbon).  When such a mixture is heated until reaction occurs, a solid residue of potassium carbonate is produced.  The explosive force of the gunpowder comes from the fact that two gases are also produced (carbon monoxide and nitrogen), which increase in volume with great force and speed.  Write the balanced chemical equation for this reaction.
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Classifying Reactions by Type of Chemistry
  • Precipitation AX + BZ  ¾®  AZ + BX
  • Acid Base HX +BOH ¾® BX +H2O
  • Gas Evolution
    • H2X + BCO3 à H2O + CO2(g) + BX
    • H2X + BSO3 à H2O + SO2(g) + BX
    • NH4X + BOH à H2O + NH3(g) + BX
  • Oxidation Reduction A+2 + B  ¾®  A + B+2
    • Combustion CxHxOx+O2àCO2 + H2O
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Classifying Reactions by what Atoms Do
  • Combination/Synthesis A + Z  ¾®  AZ
  • Decomposition AZ  ¾®  A + Z
  • Single Displacement     A + BZ  ¾®  AZ + B
  • Double displacement   AX + BZ  ¾®  AZ + BX
    • Neutralization HX +BOH ¾® BX +H2O
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Writing ionic equations
  • Soluble ionic substances are written as ions.
  • Strong acids and bases are written as ions.
        • HClO4 NaOH,
        • H2SO4 KOH
        • HBr Ba(OH)2 (slightly soluble)
        • HCl            all other soluble hydroxides
        • HNO3
  • Weak acids and bases are written in the undissociated form.
  • Weak electrolytes or insoluble salts written as molecular formula.
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Solubility Rules
  • Alkali metals and NH4+ compounds are soluble.
  • Nitrates(NO3-), acetates (CH3CO2-), chlorates (ClO3-), perchlorates(ClO4-), and sulfates(SO4-2) are generally soluble (except for Sr+2, Ca+2, Ba+2, Pb+2, and Hg2+2 sulfates).
  • Chlorides(Cl-), bromides(Br-), iodides(I-), are soluble (except for Silver(Ag+),mercury(I)(Hg2+2), and lead(II)( Pb+2) halides).
  • Most compounds not included above are not soluble.
    • i.e. Sulfides(S-2), carbonates(CO3-2), phosphates(PO4-3), chromates(CrO4-2), Oxides (O-2), and Hydroxides(OH-)
      •  (Ca(OH)2, CaO, Sr(OH)2, SrO, Ba(OH)2 and BaO are slightly soluble.)
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"Ba2"
  • Ba2+ (aq) is toxic to humans.  However, when physicians need to x-ray the gastrointestinal (GI) tract – stomach and intestines – they fill the patients GI tract with barium sulfate and water.  How can it be that the patient is not harmed by this procedure?
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Predicting reactions
  • K2S  +  CuSO4 à
  • Na2CrO4  +  Pb(C2H3O2)2 à
  • ZnBr2  +  K3PO4  à
  • KOH  +  NH4Cl à
  • NH3  +  FeCl3  à
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REDOX Reactions
  • Oxidation number -   In order to keep track of electrons in chemical reactions, chemists assign an oxidation number to each element.
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Determining Oxidation States
  • Oxidation number of an element in its native state is zero.
  • Alkali metals have an oxidation number of +1
  • Alkaline earth elements have an oxidation number of +2
  • The oxidation number of monatomic ions is the same as the charge.
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Determining Oxidation States
  • Fluorine is -1 except for F2.
  • Cl, Br, and I are -1 in binary compounds.
  • O is usually -2 (except for peroxides O2-2 and superoxides O2-1).
  • H is usually +1 (except for hydrides H-1)
  • The sum of the oxidation numbers equals the charge on ion or molecule.
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Try some
  • Ga2O3    Fe2(CrO4)3


  • K2MnO4 Hg2(BrO3)2


  • H2PO4- KClO4
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"Oxidation – process in which..."
      • Oxidation – process in which an element loses one or more electrons with an increase in the oxidation number.


      • Reduction – process in which an element gains one or more electrons with a decrease in oxidation number.
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"Oxidizing agent – Substance that..."

      • Oxidizing agent – Substance that causes another substance to be oxidized.  The oxidizing agent is always reduced.


      • Reducing agent – Substance that causes another substance to be reduced.  The reducing agent is always oxidized.
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"hydrogen"
  • hydrogen
  • tungsten
  • WO3
  • H2
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"Carbon"
  • Carbon
  • Tin
  • SnO2(s)
  • C(s)
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Half Reaction Method of Balancing Redox Reactions
  • Write skeleton ionic reaction.  (Usually a given.)
  • Split into 2 half reactions, one for oxidation and one for reduction.  (Determine what  is oxidized and what is reduced by calculating oxidation numbers.  Remember LEO says GER  Loses Electrons Oxidation, Gains Electrons Reduction)
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Half Reaction Method of Balancing Redox Reactions
  • Balance each half reaction.
    • balance all but H and O.
    • balance O by adding H2O.
    • balance H by adding H+.
    • balance charge by adding electrons.
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Half Reaction Method of Balancing Redox Reactions

  • Add half reactions together after multiplying by a factor to be sure electrons cancel.
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Half Reaction Method of Balancing Redox Reactions
  • This method provides an equation for a reaction occurring in acid.  To change to a balanced basic reaction add
  • H+  +  OH-  ®  H2O
  • to the reaction to cancel out all H+’s.
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Balance in acid
  • Cr2O72-(aq) + Cl-1(aq) à Cr3+(aq) + Cl2(g)



  • 14H+(aq) + Cr2O72-(aq) + 6Cl-1(aq)
  •                  à 2Cr3+(aq) + 3Cl2(g) + 7 H2O(l)
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Balance in acid
  • MnO2(s) + Hg(l) + Cl-1(aq)
  •                                à Mn+2(aq) + Hg2Cl2(s)


  • 4H+(aq) + MnO2(s) + 2Hg(l) + 2Cl-1(aq)
  •              à Mn+2(aq) + Hg2Cl2(s) + 2H2O(l)
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Balance in acid
  • Ag(s) + NO3-1(aq) à Ag+1(aq) + NO(g)



  • 4H+(aq) + 3Ag(s) + NO3-1(aq)
  •                  à 3Ag+1(aq) + NO(g) + 2 H2O(l)
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Balance in acid
  • H3AsO4(aq) + Zn(s) à AsH3(g) + Zn+2(aq)



  • 8H+(aq) + H3AsO4(aq) + 4Zn(s)
  •                à AsH3(g) + 4Zn+2(aq) + 4 H2O(l)
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Balance in acid
  • Au+3(aq) + I2(s) à Au(s) + IO3-1(aq)



  • 10Au+3(aq) + 3I2(s) + 18 H2O(l)
  •             à 36H+(aq) + 10Au(s) + 6IO3-1(aq)
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Balance in acid
  • IO3-1(aq) + I-1(aq) à I3-1(aq)



  • 6H+(aq) + IO3-1(aq) + 8I-1(aq)
  •                          à 3I3-1(aq) + 3 H2O(l)
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Balance in acid
  • HS2O3-1(aq) à S(s) + HSO4-1(aq)



  • H+(aq) + 3HS2O3-1(aq)
  •                  à 4S(s) + 2HSO4-1(aq) + H2O(l)
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Balance in acid
  • O2-2(aq) à O2(g) + H2O(l)



  • 4H+(aq) + 2 O2-2(aq) à O2(g) + 2H2O(l)
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Balance in acid
  • Cr2O7-2(aq) + I2(aq) à Cr+3(aq) + IO3-1




  • 34H+(aq) + 5Cr2O7-2(aq) + 3I2(aq)
  •               à 10Cr+3(aq) + 6IO3-1 + 17H2O(l)
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Balance in acid
  • S2O3-2(aq) + I2(aq) à S4O6-2(aq) + I-1(aq)



  • 2S2O3-2(aq) + I2(aq) à S4O6-2(aq) + 2I-1(aq)
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Balance in acid
  • MnO4-1(aq) + H2O2(aq) à Mn+2(aq) + O2(g)



  • 6H+(aq) + 2MnO4-1(aq) + 5H2O2(aq)
  •                 à 2Mn+2(aq) + 5O2(g) + 8 H2O(l)
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Balance in acid
  • Hg2Cl2(s) + NO2-1(aq) à Hg+2(aq) + NO(g)



  • 4H+(aq) + Hg2Cl2(s) + 2NO2-1(aq)
  • à 2Hg+2(aq) + NO(g) + 2Cl-1(aq) +2H2O(l)
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Balance in acid
  • MnO4-2(aq) à MnO2(s) + MnO4-1(aq)



  • 4H+(aq) + 3MnO4-2(aq)
  •          à MnO2(s) + 2MnO4-1(aq) + 2H2O(l)
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Balance in acid
  • Pb(s) + PbO2(s) + SO4-2(aq) à PbSO4(s)



  • 4H+(aq) + Pb(s) + PbO2(s) + 2SO4-2(aq)
  •                        à 2PbSO4(s) + 2H2O(l)
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Balance in base
  • Co(OH)3(s) + Sn(s)
  •                       à Co(OH)2(s) + HSnO2-1(aq)


  • OH-1(aq) + 2Co(OH)3(s) + Sn(s)
  •       à 2Co(OH)2(s) + HSnO2-1(aq) + H2O(l)
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Balance in base
  • ClO4-1(aq) + I-1(aq)
  •                          à ClO3-1(aq) + IO3-1(aq)


  • 3ClO4-1(aq) + I-1(aq)
  •                          à 3ClO3-1(aq) + IO3-1(aq)
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Balance in base
  • PbO2(s) + Cl-1(aq)
  •                       à ClO-1(aq) + Pb(OH)3-1(aq)



  • OH-1(aq) + H2O(l) + PbO2(s) + Cl-1(aq)
  •                        à ClO-1(aq) + Pb(OH)3-1(aq)
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Balance in base
  • NO2-1(aq) + Al(s) à NH3(g) + AlO2-1(aq)



  • OH-1(aq) + H2O(l) + NO2-1(aq) + 2Al(s)
  •                                à NH3(g) + 2AlO2-1(aq)
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Balance in base
  • ClO-1(aq) à Cl-1(aq) + O2(g)



  • 2ClO-1(aq) à 2Cl-1(aq) + O2(g)
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Balance in base
  • HXeO4-1(aq) + Pb(s)
  •                             à Xe(g) + HPbO2-1(aq)


  • 2OH-1(aq) + HXeO4-1(aq) + 3Pb(s)
  •                             à Xe(g) + 3HPbO2-1(aq)
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Balance in base
  • Ag2S(s) + CN-1(aq) + O2(g)
  •                                à S(s) + AgCN(aq)


  • 2 H2O(l) + 2Ag2S(s) + 4CN-1(aq) + O2(g)
  •           à 2S(s) + 4AgCN(aq) + 4OH-1(aq)
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Balance in base
  • MnO4-1(aq) + S-2(aq) à MnS(s) + S(s)



  • 8 H2O(l) + 2MnO4-1(aq) + 7S-2(aq)
  •                  à 2MnS(s) + 5S(s) + 16OH-1(aq)
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Balance in base
  • Cl2(g) à ClO-1(aq) + Cl-1(aq)



  • 2OH-1(aq) + Cl2(g)
  •                    à ClO-1(aq) + Cl-1(aq) + H2O(l)
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Balance in base
  • MnO4-1(aq) + H2O2(aq) à MnO2(s) + O2(g)



  • 2MnO4-1(aq) + 3H2O2(aq)
  •               à 2MnO2(s) + 3O2(g) + 2OH-1(aq)
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Balance in base
  • ClO2(aq) à ClO2-1(aq) + ClO3-1(aq)



  • 2OH-1(aq) + 2ClO2(aq)
  •              à ClO2-1(aq) + ClO3-1(aq) + H2O(l)
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Balance in base
  • CrO4-2(aq) + N2H4(aq) à Cr+3(aq) + N2(g)



  • 4CrO4-2(aq) + 3N2H4(aq) + 4H2O(l)
  •             à 4Cr+3(aq) + 3N2(g) + 20 OH-1(aq)
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Balance in base
  • Ag(s) + CN-1(aq) + O2(g)
  •                       à Ag(CN)2-1(aq) + OH-1(aq)



  • 4Ag(s) + 8CN-1(aq) + O2(g) + 2H2O(l)
  •                     à 4Ag(CN)2-1(aq) + 4OH-1(aq)
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Balance in base
  • Co(s) + ClO-1(aq)à Co+2(aq) + Cl-1(aq)



  • Co(s) + ClO-1(aq) + H2O(l)
  •                 à Co+2(aq) + Cl-1(aq) + 2OH-(aq)
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Balance in base
  • Cd(s) + H2O(l) + Ni2O3(s)
  •                                 à Cd(OH)2(s) + NiO(s)


  • Cd(s) + H2O(l) + Ni2O3(s)
  •                               à Cd(OH)2(s) + 2NiO(s)