Hydrated metal ions Charged metals ions also produce an acidic Acidity of hydrated metal ions solution. The metal itself does not act as a Brønsted-Lowry M = metal acid, but instead forms a hydrate that acts as a For Mn+, a small, highly charged ion, Brønsted-Lowry acid. n+ (n-1) + Salts and Molecular Structure M(H2O)x + H2O ⇌ M(H2O)x-1OH + H3O Typically the higher the charge on the metal ion, stronger the acidity of the hydrated ion. Calculate the pH of a 0.010 M AlCl3 solution. The Ka Cu2+ + 5 H O Cu(H O) 2+ 3+ -5 2 2 5 value for Al(H2O)6 is 1.4 x 10 . 2+ 2+ + Cu(H2O)5 CuOH(H2O)4 + H Salts of weak acids and bases Problem Molecular Trends in Acid For salts from a weak acid and weak base, the Predict whether an aqueous solutions of each of Ka and Kb of the ions must be compared. the following salts will be acidic, basic, or Strength neutral. If Ka > Kb the solution will be acidic K Al(H O) 3+ =1.4 x 10-5 NH C H O a 2 6 If Ka < Kb the solution will be basic 4 2 3 2 -4 Ka HF = 7.2 x 10 If K = K the solution will be neutral NH4CN - -2 a b Ka HSO4 = 1.2x10 Al2(SO4)3 - -10 Kb C2H3O2 = 5.6x10 NH F - -5 4 Kb CN = 1.6x10 -5 Kb NH3 = 1.8 x 10 Trends in Binary Nonmetal Oxyacids Hydride Activity Halogen Strong Acids With the same number of oxygen atoms This applies to nonmetals only All halogens are strong acids except fluorine. around a central nonmetal (E), acid strength increases with the From left to right, electronegativity All halogens have a high electronegativity. The increases, polarity increases. H+ removal short bond length of fluorine makes is a weak electronegativity of E. is easier, and acidity increases. acid. HClO > HBrO > HIO From top to bottom, bond length With different numbers of oxygen atoms increases, bond strength decreases, around E, acid strength increases with the H+ removal is easier, and acidity number of oxygen atoms. increases. This is because oxygen atoms pull the electron density away from E, and H+ is more easily removed. 1 Leveling Effect Strong oxyanion acids It is difficult to differentiate the If there are at least 2 more oxygen atoms than strengths of strong acids or bases because hydrogen atoms, the acid will be strong. of water. Water can act like an acid or a base. H SO , HNO , HClO , HClO 2 4 3 3 4 By LeChâtelier’s principle, the stronger the acid or base, the more water will shift to neutralize it. Weak acids or bases are limited by their conjugate bases or acids, strong acids and base are limited by water. Acidic Oxides (Acid Anhydrides) Basic Oxides (Basic Anhydrides) Leveling effect Water “levels” all strong acids (or Nonmetal oxides For metal oxides bases) to an equal strength (HCl, HBr, . O-X bond is strong and covalent. O-X bond is ionic. K O, CaO and HI). SO2, NO2, CO2 2 To determine the strength, Ka, of When H-O-X grouping is dissolved in water, the O-X If X has a very low electronegativity, the O-X bond will strong acids you have to dissolve it in bond will remain intact. It will be the polar and be ionic and subject to being broken in polar water, an acid (weaker base than water), such relatively weak H-O bond that will tend to break, producing a basic solution. as acetic acid, where different levels releasing a proton. K2 O + H2O KOH of protonation can occur. SO2 + H2O H2SO3 + - H2SO3 + H2O ⇌ H + HSO3 Lewis Acids and Bases Lewis Acids and Bases Acid base models Lewis acid: electron pair acceptor This is the broadest definition. Lewis base: electron pair donor An acid is an electron pair acceptor. A base is an electron pair donor. 33++ This is useful for: electron deficient compounds, H HH 3+ H polar double bonded compounds, metal ions, AlAl3+ ++ 6 6 OO Al O + Al O and protons (H ). HH H H66 Lewis acid Lewis base 2 Acidic Solutions Containing Common Ion Common Ions. A common ion is one that is both dissolved in an Acid-base Equilbria + aqueous solution and introduced to the existing The equilibrium concentration of H3O equilibrium system. in a 1.0 M HF solution is 2.7 x 10-2 M, The shift in equilibrium as a result of the introduction and the percent dissociation of HF is of a common ion is called the common ion effect. 2.7%. Chapter 15 Calculate [H O+ ] and the percent This is an application of Le Châtelier’s Principle. 3 dissociation of HF in a solution -4 containing 1.0 M HF (Ka = 7.2 x 10 ) and 1.0 M NaF. *assume NaF dissociates at 100% 3.