chap 15

• Bronsted acid


  Proton donor
• Bronsted base


  Proton acceptor
• Conjugate acid-base pair


  Species that differ by a single proton
• Acid-base reaction


  Proton (hydrogen ion, H+) transfer
• The generalization of the Arrhenius definition of acids and bases is called the Brønsted-Lowry definitions
• Acid (Brønsted-Lowry)


  Proton donor
• Base (Brønsted-Lowry)


  Proton acceptor
• HCl is the acid because it donates a proton. Water is the base because it accepts a proton.
• Conjugate acid-base pair


  Members differ by a single proton
• Amphoteric substance


  Can act as either an acid or base
• The hydrogen carbonate ion (HCO3-) is an amphoteric substance
• Strong acid


  Reacts completely with water (like HCl and HNO3)
• Weak acid


  Less than completely ionized
• Strong base


  Reacts completely (like the oxide ion)
• Weak base


  Undergoes incomplete reactions (like NH3)
• The strongest acid in water is the hydronium ion, H3O+
• The strongest base that can be found in water is the hydroxide ion, OH-
• Acetic acid (HC2H3O2)


  A weak acid that ionizes only slightly in water
• Position of acid-base equilibrium


  Favors the weaker acid and base
• Stronger acids and bases tend to react with each other to produce their weaker conjugates
• The hydronium ion is a better proton donor than acetic acid (it is a stronger acid)
• The acetate ion is a better proton acceptor than water (it is a stronger base)
• The stronger a Brønsted acid is, the weaker is its conjugate base
• Common Binary Acids


  • HCl(aq) (Hydrochloric, Strong)
  • HBr(aq) (Hydrobromic, Strong)
  • HI(aq) (Hydroiodic, Strong)
  • HF(aq) (Hydrofluoric, Weak)
  • H2S (Hydrosulfuric, Weak)
  • H2Se (Hydroselenic, Weak)
• The strengths of the binary acids increase from left to right within the same period
• The strengths of the binary acids increase from top to bottom within a group
• Examples of Oxoacids


  • H2SO4 (Sulfuric, Strong)
  • H2SeO4 (Selenic, Strong)
  • HNO3 (Nitric, Strong)
  • HClO4 (Perchloric, Strong)
  • H3PO4 (Phosphoric, Weak)
  • HNO2 (Nitrous, Weak)
  • H2CO3 (Carbonic, Weak)
• When the central atom holds the same number of oxygen atoms, the acid strength increases from bottom to top within a group and from left to right within a period
• For a given central atom, the acid strength of an oxoacid increases with the number of oxygens held by the central atom
• Sulfuric acid is a stronger acid than phosphoric acid in terms of the percentage of molecules that are ionized
• The strengths of oxoacids generally depend on the polarity of the O-H bond(s)
• The stronger an acid, the weaker and more stable is its conjugate base
• Presence of electronegative atoms (halide, nitrogen or other oxygen) near —COOH group makes the organic acid stronger
• Lewis acid


  Any ionic or molecular species that can accept an electron pair
• Lewis base


  Any species that can donate an electron pair
• C2O4(2-)(aq)

  Oxalate ion
• NO2-(aq)

  Nitrite ion
• OCN-(aq)

  Cyanate ion
• AsH3 < H2Se < HBr
• HBrO < HBrO2 < HBrO3 < HBrO4