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Chapter 4: Chemical Reactions. Chemistry 1061: Principles of Chemistry I Andy Aspaas, Instructor. Chemical reactions. Ions in aqueous solution Molecular and ionic equations Types of reactions Precipitation reactions Acid-base reactions Oxidation-reduction reactions Solutions

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chapter 4 chemical reactions
Chapter 4: Chemical Reactions

Chemistry 1061: Principles of Chemistry I

Andy Aspaas, Instructor

chemical reactions
Chemical reactions
  • Ions in aqueous solution
    • Molecular and ionic equations
  • Types of reactions
    • Precipitation reactions
    • Acid-base reactions
    • Oxidation-reduction reactions
  • Solutions
    • Concentration and dilutions
  • Quantitative analysis
    • Gravimetric and volumetric analyses
ions in aqueous solutions
Ions in aqueous solutions
  • Ionic theory of solutions: Arrhenius, 1884
    • When dissolved in water, the individual ions of ionic substances completely separate and enable the solution to conduct electricity
    • Pure water is a poor conductor of electricity
  • Electrolyte: substance that dissolves in water to give an electrically conducting solution
    • Generally, ionic solids that dissolve in water are electrolytes
    • A few molecular electrolytes, Ex. HCl (g)
    • Nonelectrolytes: dissolve in water, poorly conducting solution, usually neutral molecular substances
strong and weak electrolytes
Strong and weak electrolytes
  • The extent to which a solution conducts electricity indicates the “strength” of the dissolved electrolyte
    • Strong electrolytes: exist in solution almost entirely as ions
      • Ex. NaCl
    • Weak electrolytes: dissolve in water to give only a small percentage of dissociated ions
      • Ex. NH3
solubility rules
Solubility rules
  • Solubility: ability of a substance to dissolve completely in water
    • Ex. Sugar, NaCl, ethyl alcohol are soluble
    • Ex. Calcium carbonate, benzene are insoluble
  • Soluble ionic compounds are strong electrolytes
    • 8 solubility rules can determine whether an ionic compound is soluble or not
solubility rules1
Solubility rules

Li+, Na+, K+, NH4+

molecular and ionic equations
Molecular and ionic equations
  • Molecular equation: chemical equation in which reactants and products are written as if they were molecular substances, even if they exist as ions in solution
    • Explicit in the actual compounds added to a solution, and the products obtained
  • Complete ionic equation: all strong electrolytes are written as their dissociated ions (aq)
    • Insoluble compounds are written as a solid compound, not ions
net ionic equations
Net ionic equations
  • Spectator ion: ion in an ionic equation that does not take part in the reaction
    • Appears in ionic form on both sides of a reaction
  • Net ionic equation: equation in which all spectator ions have been canceled
  • Several different reactions can have the same net ionic equation
precipitation reactions
Precipitation reactions
  • Precipitate: insoluble compound formed during a chemical reaction in solution
  • Predicting precipitation reactions:
    • Exchange reaction most common, each compound “trades partners” to form products
    • Write molecular equation
    • Use solubility rules to determine phase lables for each product and reactant; (aq) if soluble, (s) if insoluble
    • If all components of reaction are soluble, no reaction occurs
    • If a product is insoluble, it forms as a precipitate
    • A net ionic equation shows the reaction at the ionic level
acid base reactions
Acid-base reactions
  • Acids: vinegar (acetic acid), lemon juice (citric acid), Coca-Cola (phosphoric acid and carbonic acid), battery acid (sulfuric acid)
  • Bases: Drano (sodium hydroxide), ammonia, Milk of Magnesia (magnesium hydroxide)
  • Brønsted-Lowry acid: molecule or ion that donates a proton to another species in a proton-transfer reaction
  • Brønsted-Lowry base: molecule or ion that accepts a proton in a proton transfer reaction
strong acids and strong bases
Strong acids and strong bases
  • Strong acids and bases ionize completely in water
    • Strong acids: HClO4, H2SO4, HI, HBr, HCl, HNO3
    • Strong bases: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
  • Weak acids and bases only partly ionize in water
neutralization reactions
Neutralization reactions
  • Reaction between acid and base to produce a salt and possibly water
    • Salt: ionic compound formed in neutralization reaction
  • Start by writing molecular equation
    • Acid anion and base cation form the salt
    • Water is usually a product
  • Net ionic equation: write any strong acid or base as its dissociated ions
acid base reactions with gas formation
Acid-base reactions with gas formation
  • Carbonates (CO32-) form H2O and CO2 when reacted with acids
  • Sufites (SO32-) form H2O and SO2 when reacted with acids
  • Sulfides (S2-) form H2S when reacted with acids
oxidation reduction reactions
Oxidation-reduction reactions
  • Oxidation-reduction reactions (redox) involve transfer of electrons
  • Oxidation number: actual charge of an atom if it exists as a monatomic ion, or a hypothetical charge assigned by a few rules
    • Elemental atoms always have ox. # 0
    • Oxygen is usually -2
    • Hydrogen is usually +1
    • Halogens usually -1 (unless bonded to another halogen or oxygen)
    • Sum of ox. #’s of atoms in a compound is 0, sum of ox #’s in a polyatomic ion is the charge on the ion
describing oxidation reduction reactions
Describing oxidation-reduction reactions
  • If a species loses electrons, it is oxidized
  • If a species gains electrions, it is reduced
    • LEO, GER
  • Use oxidation numbers to determine this
  • Oxidizing agent: species that oxidizes another species, and is itself reduced
  • Reducing agent: species that reduces another species, and is itself oxidized
combustion reaction
Combustion reaction
  • Reaction in which a substance reacts with oxygen, usually accompanied by release of heat and production of a flame
  • Organic compounds combust to form CO2 and H2O
  • Metals combust to form metal oxides
molar concentration
Molar concentration
  • Molarity: measure of concentration

= (moles of solute / liters of solution)

    • Unit: mol/L
  • Diluting solutions: MiVi = MfVf
gravimetric analysis
Gravimetric analysis
  • Determination of amount of a species by precipitating that species out as an insoluble compound, and weighing the product
  • Mass precipitated product  moles product  moles unknown species  mass unknown species
volumetric analysis
Volumetric analysis
  • Titration: method for determining amount of one substance by adding a precise volume of another substance until the two substances completely react
  • Colored pH indicator often used to detect endpoint
  • Volume added solution  moles added solution  moles unkn. solution  molarity or grams unkn. solution
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