Why is Ammonia (NH3) a Weak Base? An Arrhenius Base is a substance that, when dissolved in water, increases the concentration of hydroxide ions. NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) H H +1 H N H H N H H Remember also that An Arrhenius Acid is a substance that, when dissolved in water, increases the concentration of hydrogen ions.

Acid and Base Anhydrides Acid Anhydrides: a compound (such as an oxide) that reacts with water to give acidic solutions Basic Anhydrides: a compound (such as an oxide) that reacts with water to give basic solutions Acidity Increases Oxides Increasing Basicity Basic Anhydride Increasing Acidity Acidic Anhydride Basicity Increases

Acid-Base Titrations Titrations are used to determine the amounts of substance present in a sample (solution). End point Known conc of acid V Unknown amount (concentration) of base Could we reverse the order?

The End Point HA(g) H+(aq) + A-(aq) BOH(s) B+(aq) + OH-(aq) The End Point for a good titration is the EQUIVALENCE point, i.e., the point at which the amount of base in the beaker equals the amount of acid disposed from the buret, i.e., nA = nB if both acid and base are one-equivalent, i.e., HA(g) H+(aq) + A-(aq) BOH(s) B+(aq) + OH-(aq) In contrast, a two-equivalent acid given by: H2A(g) 2 H+(aq) + A2-(aq) would result in 2 nA = nB. The concentration of the base simply follows as nB/VB.

Do Acids Do More than Neutralize Bases? Discuss/Demonstrate Acid on a carbonate Acid on a metal Acid on a metal oxide

Do Bases Do More than Neutralize Acids? Discuss/Demonstrate Base (except ammonia) on an ammonium salt Base on the oxide of a nonmetal

Redox Reactions or Oxidation-Reduction Reactions Loss of Electrons = Oxidation Gain of Electrons = Reduction How do I remember this? LEO, the lion, says GER

Oxidation and Reduction Loss of 2 electrons = Oxidation Mg(s) + Cl2(g) MgCl2(s) Each chlorine atom gains one electron = Reduction Loss of 2 electrons = Oxidation 2 Mg(s) + O2(g) 2 MgO(s) Each oxygen atom gains two electrons = Reduction

Reducing Agent: A substance that causes the reduction of another substance while being oxidized itself. Good reducing agent: H2. Oxidizing Agent: A substance that causes the oxidation of another substance while being reduced itself (gains electrons). Strong oxidizing agents: O2, F2, Cl2, Br2 ±0 ±0 +2 -2 2 Mg(s) + O2(g) 2 MgO(s) ±0 ±0 +1 -1 2 Na(s) + Cl2(g) 2 NaCl(s) reducing agent oxidizing agent

Oxidation Number Oxidation Numbers is a parameter obtained by exaggerating the ionic character of a bond. It can be understood as the charge that an atom would have if the more electronegative atom in a bond acquired the two electrons of the bond completely. +2 -2 +5 -2 MgO +6 -2 NO3- SO3 +1 -1 +7 -2 HCl MnO4-

The sum of the oxidation numbers of all atoms in the species is equal to its total charge. For atoms in their elemental form 0 For atoms of group 1 +1 For atoms of group 2 +2 For atoms of group 3 +3 For atoms of group 4 +4, +2 For hydrogen +1 (with non-metals) -1 (with metals) For fluorine -1 (always) For oxygen -2 (unless with F) -1 (in peroxides, O22-) -1/2 (in superoxides, O2-) For halogens (not F) -1 in most compounds (unless with O or a more electronegative halogen)

Determining Oxidation Numbers SO2 CCl4 COCl2 H2O2 O2 OH- MgH2 CaCO3 I2

Electron Transfer Reactions = Redox Chemistry An atom is oxidized (loses an electron) when its oxidation number increases in a chemical reaction. An atom is reduced (gains an electron) when its oxidation number decreases in a chemical reaction. C + O2 CO2 ±0 -2 reduced oxidized +4