Lecture 10/20/99 Chapter 5, Section 5-7

Anouncements

  1. Chapter 5 Assignment: Due Monday 10/25/99 5:00 pm Chapter 5 Homework Set and Questions: 8,22,30,36,44,54,58,60,72,74,82,106,112

Reactions of Acids and Bases

  1. Definitions of acids and bases
    1. Arrhenius definition (in water only)
      1. Acids, produce H+ in water solution

        HCl (aq) -> H+(aq) + Cl-

      2. Bases, produce OH- in water solution

        NaOH(aq) -> Na+ + OH-

    2. Bronsted-Lowry Acids and bases (more general definition)
      1. Acids are proton donors in a chemical reaction

        HCl (g) + H2O -> H3O+ + Cl-
        Acid + Base -> Base + Acid

      2. Bases are proton acceptors in a chemical reaction

        NaOH + H2O -> Na+ + H3O+
        Base + Acid -> Acid + Base

  2. Common Acids (know names of all strong acids)
    1. Monoprotic - Single H+
    2. Polyprotic - more than 1 H+, ie: diprotic, triprotic

      H2SO4 + H2O -> H3O1+ + HSO41-
      HSO41- + H2O -> H3O1+ + SO42-

    3. Strong acids (dissociate completely)
    4. Weak acids (partially dissociate, introduce equlibrium)
  3. Common Bases
    1. Strong Bases (alkali metal hydroxides)
    2. Weak bases (ammonia)
  4. Aqueous Acid-Base Reactions
    1. Total Equation

      HCl(aq) + NaOH(aq) -> H2O(l) + NaCl(aq)

    2. Ionic Equations
      1. Dissociation

        HCl (g) -> H+(aq) + Cl-(aq)
        OR HCl(g) + H2O(l) -> H3O+(aq) + Cl-(aq)
        NaOH -> Na+(aq) + OH-(aq)

      2. Neutralization (spectator ions)

        H3O+ + Cl- + Na+ + OH- -> 2 H2O + Na+ + Cl-

      3. Net Ionic Equation

        H3O+ + OH- -> 2 H2O

  5. Magnesium Hydroxide + Nitric Acid
    1. Students work out:
      1. Total equation
      2. Ionic Equation
      3. Net ionic equation
    2. Solutions
      1. Balanced total equation

        Mg(OH)2 (aq) +2 HNO3(aq)-> 2 H2O +Mg(NO3)2 (aq)

      2. Total Ionic Equation

        Mg2+ + 2 OH1- + 2 H1+ + 2NO31- - > 2H2O + Mg2+ + 2 NO31-

      3. Net Ionic Equation

        2 OH1- + 2 H1+ -> 2H2O

  6. Sulfuric acid and lithium hydroxide
    1. Students work out:
      1. Total equation
      2. Ionic Equation
      3. Net ionic equation
    2. Solutions
      1. Total equation:

        H2SO4 (aq) + 2 LiOH (aq) -> 2 H2O + Li2SO4 (aq)

      2. Ionic Equation:

        2 H1+ (aq) + SO42- (aq) + 2 LI1+ (aq) + 2 OH1- -> 2 H2O + SO42- (aq) + 2 Li1+ (aq)

      3. Net ionic equation

        2 H1+ (aq) + 2 OH1- -> 2 H2O

  7. Acetic acid and iron (III) hydroxide
    1. Students work out:
      1. Total equation
      2. Ionic Equation
      3. Net ionic equation
    2. Solutions
      1. Total equation

        3 CH3COOH (aq) + Fe(OH)3 (s) -> 3 H2O + Fe(CH3COO)3 (aq)

      2. Ionic Equation

        3 CH3COO1- + 3H1+ (aq) + Fe3+(aq) + 3 OH1- (aq) ->
        3 H2O + Fe3+ (aq) + 3 CH3COO1- (aq)

      3. Net ionic equation

        3H1+ (aq) + 3 OH1- (aq) -> 3 H2O

  8. Ammonia (NH3) and water(CD-ROM d: h: Internet)
    NH3 + H2O -> NH41+ (aq)+ OH1-(aq)
  9. hydrochloric acid and ammonia produces ammoinum and chloride
    HCl (aq) + NH3(aq) - > NH41+ (aq) + Cl1-(aq)
  10. hydrochloric acid and sodium hydroxide produces sodium chloride and water; no indicator
    HCl(aq) + NaOH(aq)-:gt; H2O + NaCl(aq)

Redox Reactions

  1. Introduction
  2. Definitions
    1. Oxidation; loss of electrons, increase charge, ie: Na -> Na1+
    2. Reduction; gain of electrons, reduce charge, ie Cl2 -> 2 Cl1-
  3. Calculating Oxidation States
    1. Elements have an oxidation state of 0 in natural state
    2. For monoatomic ions, is charge
    3. Oxygen is usually 2-, unless peroxide, then 1-
    4. Hydrogen is usually 1+, except metal hydrides (NaH) then 1-
    5. Sum of oxidation states for a compound is 0
    6. Sum of oxidation states for polyatomic ion is charge
  4. Examples of oxidation numbers:
    Compound Oxidation Number
    NaCl Na1+ Cl1-    
    MgF2 Mg2+ F1-    
    O2 O0      
    Na2SO3 Na1+ S4+ O2-  
    PF3 P3+ F1-    
    CrO3 Cr6+ O2-    
    Cr2O72- Cr6+ O2-    
    (NH4)3PO4 N3- H1+ P5+ O2-
    Cl2 Cl0      
    ClO1- Cl1+ O2-    
    ClO21- Cl3+ O2-    
    ClO31- Cl5+ O2-    
    ClO41- Cl7+ O2-    
  5. Redox reactions (check balance and oxidation numbers)
    1. Electrolysis of water

      2 H2O -> 2 H2 + O2

    2. Oxidation of iron

      4 Fe + O2 -> 2 Fe2O

    3. Solution Redox reaction. Excess acid and sodium dichromate and sulfurous acid react to produce chromium (III) sulfate and water.

      5 H1+ (aq) + Cr2O7-2 (aq) + 3 HSO31- (aq) ->

      2 Cr3+ (aq) + 3 SO42- (aq) + 4 H2O

      1. Balance OK, check each element and total charge on each side.
      2. Oxidation Numbers
        Reactant Oxidation Number
        H1+ H1+    
        Cr2O72- Cr6+ O2-  
        HSO31- H1+ S4+ O2-
        Cr3+ Cr3+    
        SO42- S6+ O2-  
        H2O H1+ O2-  
      3. Cr is reduced from Cr6+ to Cr3+
      4. S is oxidized from S4+ to S6+
    4. Zinc in nitric acid:

      Zn (s) + 4 HNO3 ->
      Zn2+ (aq) + 2 NO2 (g) + 2 H2O + 2 NO31- (aq)

    5. Photochemistry of NO NO (g) + O3 (g) - > NO2 (g) + O2 (g)
      NO2 (g) + OH (g) -> HNO3 (g)