Special Substances

IV. Strength of conjugates The stronger the acid or base is, the weaker its conjugate base. For example, HCl is a strong acid so its conjugate base, Cl-, is a weak base.

V. Special Substances A. Some substances can be either an acid or a base depending on the substance it is with. These substances are called amphoteric. 1. Must have hydrogen to act as acid 2. Can be a compound or ion. 3. Examples: water, HCO3-

VI. Anhydrides: oxides that create acid or base in water 1. Metal oxides create bases in water (hydroxides) Na2O in water creates NaOH 2. Nonmetal oxides create acids in water NO2 in water creates HNO3 SO2 in water creates H2SO3 (components of acid rain)

VI. Neutralization Reactions A. Neutralization occurs when the hydrogen (hydronium) ions of an acid react completely with the hydroxide ions of a base to form water molecules. B. The products of neutralization are always water and a salt. 1. A salt is composed of the cation from a base and the anion from an acid. (Front half can’t be hydrogen, back half can’t be hydroxide or oxide.) 2. Example: HCl + NaOH → NaCl + H2O

VII. Ionization constant of water (K w ) A. H2O + H2O → H3O + + OH - B. Concentration of the two ions at room temperature in pure water are each 1 x M C. The product of the two equals 1 x This product is constant at room temp and is given the symbol Kw. Kw = [H3O + ][OH - ] = 1 x D. If one of the ion concentrations are known, the other may be calculated.

E. Examples 1. If the hydronium ion concentration is 1.0 x M, what is the concentration of the hydroxide ion? 1 x = 1.0 x M 1.0 x Determine the hydronium ion concentration in a 3.0 x M HNO3 solution. In a strong acid: #H (concentration) = [H + ] (or [H3O + ]) [H + ] = 1(3.0 x ) = 3.0 x M 3. Determine the hydronium and hydroxide ion concentrations in a 1.0 x M Ca(OH)2 solution. In a strong base: #OH (concentration) = [OH - ] [OH - ] = 2(1.0 x ) = 2.0 x M [H3O + ] = 1 x = 5.0 x M 2.0 x 10 -4