Acid-Base Properties of Salts Salt = ionic compound Dissolving in water will break it into its ions which can behave like acids or bases

Salts Producing Neutral Solutions Claudia Witt: List strong bases (circle cations) and strong acids (circle anions) to show salts formed Salts Producing Neutral Solutions Salts that consist of the cations of strong bases and the anions of strong acids have no effect on [H+] when dissolved in water They will make a neutral solution (pH = 7)

Salts Producing Basic Solutions Start by determining which major species has the largest effect on the pH Example: aqueous solution of sodium acetate (NaC2H3O2) Ka X Kb = Kw The Ka value of the parent weak acid (acetic acid above) can be used to determine the Kb For any salt whose cation has neutral properties and whose anion is the conjugate base of a weak acid, the aqueous solution will be basic.

Practice with Kb Using the data, calculate Ka or Kb and write the reaction with water for each of the following aqueous ions: NO2-(Ka for HNO2 = 4.0 X 10-4) F- (Ka for HF = 7.2 X 10-4) C6H5NH3+ (Kb for aniline, C6H5NH2, equals 3.8 X 10-10)

Example Calculate the pH of a 0.30 M NaF solution. The Ka value for HF is 7.2 X 10-4. Answer: 8.31, basic solution

Salts Producing Acidic Solution Salts in which the anion is not a base and the cation is the conjugate acid of a weak base will produce acidic solutions Example: Calculate the pH of a 0.10 M NH4Cl solution. The Kb value for NH3 is 1.8 X 10-5. pH = 5.13

Salt Producing Acidic Solution Second Type: salt that produces an acidic solution that has a highly charged metal ion like AlCl3…Al cation has a 3+ charge A higher charged metal ion has a stronger acidity in the hydrated ion Ex: Calculate the pH of a 0.010 M AlCl3 solution when the Ka value for Al(H2O)63+ is 1.4 X 10-5 Answer: pH = 3.43

Predicting Acidity Using Ka If Ka value for the acidic ion is greater than Kb value for the basic ion, the solution will be acidic. If the Kb value is larger than Ka, the solution will be basic If Ka = Kb, the solution will be neutral

Example Predict whether an aqueous solution of each of the following salts will be acidic, basic, or neutral NH4C2H3O2 NH4CN Al2(SO4)3

Summary

Structure’s Effect Bond Strength and Polarity will determine the likelihood of it to donate/accept a hydrogen ion Bond Strength: electronegativity comes into play. Higher electronegativity = more polar = dissociates more completely in water Oxyacids (H - O - X): acid strength increases with more oxygen atoms attached to the central atom Oxygen (highly electronegative) pulls the electrons closer to one side and is more likely to produce a hydrogen ion Attached ions: greater charge of ion = more acidic

Acid Vs. Base with O-X Bonds H - O - X bond will produce an acid in water if the O-X bond is strong and covalent (X has a high electronegativity). When dissolved in water, the O-X bond will not break (the H-O bond will instead). These are called acidic oxides. If O-X bond is ionic (X has a low electronegativity), the bond will break in water and a base will be produced. These can consist of group 1A and 2A metals and are called basic oxides.