Notes 16-5 Obj. 16.9, 16.10, 16.11

16.9 Acid-Base Properties of Salt Solutions A.) Reactions of Anions with Water 1.) Anions are bases. 2.) As such, they can react with water in a hydrolysis reaction to form OH - and the conjugate acid: X - (aq) + H 2 O (l) HX (aq) + OH - (aq)

B.) Reactions of Cations with Water 1.) Cations with acidic protons (like NH 4 + ) will lower the pH of a solution. 2.) Most metal cations that are hydrated in solution also lower the pH of the solution. (cations cannot be +1, or group 1 or 2)

3.) Attraction between nonbonding electrons on oxygen and the metal causes a shift of the electron density in water. 4.) This makes the O-H bond more polar and the water more acidic. 5.) Greater charge and smaller size make a cation more acidic.

C.) Effect of Cations and Anions 1.An anion that is the conjugate base of a strong acid will not affect the pH. 2.An anion that is the conjugate base of a weak acid will increase the pH. 3.A cation that is the conjugate acid of a weak base will decrease the pH.

4.Cations of the strong Arrhenius bases will not affect the pH. 5.Other metal ions will cause a decrease in pH. 6.When a solution contains both the conjugate base of a weak acid and the conjugate acid of a weak base, the affect on pH depends on the K a and K b values.

Sample Exercise Determining Whether Salt Solutions Are Acidic, Basic, or Neutral Determine whether aqueous solutions of each of the following salts will be acidic, basic, or neutral: (a) Ba(CH 3 COO) 2, (b) NH 4 Cl, (c) CH 3 NH 3 Br, (d) KNO 3, (e) Al(ClO 4 ) 3.

Sample Exercise Determining Whether Salt Solutions Are Acidic, Basic, or Neutral In each of the following, indicate which salt in each of the following pairs will form the more acidic (or less basic) M solution: (a) NaNO 3, or Fe(NO 3 ) 3 ; (b) KBr, or KBrO; (c) CH 3 NH 3 Cl, or BaCl 2, (d) NH 4 NO 2, or NH 4 NO 3. Practice Exercise

Sample Exercise Predicting Whether the Solution of an Amphiprotic Anion is Acidic or Basic Predict whether the salt Na 2 HPO 4 will form an acidic solution or a basic solution on dissolving in water.

Sample Exercise Predicting Whether the Solution of an Amphiprotic Anion is Acidic or Basic Predict whether the dipotassium salt of citric acid (K 2 HC 6 H 5 O 7 ) will form an acidic or basic solution in water (see Table 16.3 for data). Practice Exercise

16.10 Acid-Base Behavior and Chemical Structure D.) Factors Affecting Acid Strength 1.) The more polar the H-X bond and/or the weaker the H-X bond, the more acidic the compound. 2.) So acidity increases from left to right across a row and from top to bottom down a group.

3.) In oxyacids, in which an -OH is bonded to another atom, Y, the more electronegative Y is, the more acidic the acid.

4.) For a series of oxyacids, acidity increases with the number of oxygens.

Sample Exercise Predicting Relative Acidities from Composition and Structure Arrange the compounds in each of the following series in order of increasing acid strength: (a) AsH 3, HI, NaH, H 2 O; (b) H 2 SO 4, H 2 SeO 3, H 2 SeO 4.

Sample Exercise Predicting Relative Acidities from Composition and Structure In each of the following pairs choose the compound that leads to the more acidic (or less basic) solution: (a) HBr, HF; (b) PH 3, H 2 S; (c) HNO 2, HNO 3 ; (d) H 2 SO 3, H 2 SeO Practice Exercise

5.) Resonance in the conjugate bases of carboxylic acids stabilizes the base and makes the conjugate acid more acidic.

© 2009, Prentice-Hall, Inc Lewis Acids and Bases A.) Lewis acids are defined as electron-pair acceptors. B.) Atoms with an empty valence orbital can be Lewis acids.

© 2009, Prentice-Hall, Inc. C.) Lewis bases are defined as electron-pair donors. D.) Anything that could be a Brønsted-Lowry base is a Lewis base. E.) Lewis bases can interact with things other than protons, however.

Sample Integrated Exercise Putting Concepts Together Phosphorous acid (H 3 PO 3 ) has the following Lewis structure (a) Explain why H 3 PO 3 is diprotic and not triprotic. (b) A 25.0-mL sample of a solution of H 3 PO 3 is titrated with M NaOH. It requires 23.3 mL of NaOH to neutralize both acidic protons. What is the molarity of the H 3 PO 3 solution? (c) The original solution from part (b) has a pH of Calculate the percent ionization and K a1 for H 3 PO 3, assuming that K a1 >> K a2. (d) How does the osmotic pressure of a M solution of HCl compare qualitatively with that of a M solution of H 3 PO 3 ? Explain.