1. Chapter 20 – Acids and Bases Describing Acids and Bases Hydrogen Ions and Acidity Acid-Base Theories Strengths of Acids and Bases

2. 20.1 Describing Acids & Bases Properties of Acids and Bases  The very word “acid” conjures all kinds of images: skin eating, drugs, caustic… But, what are some properties of acids and how do we begin to understand them?  Some properties: sour, conduct electricity (electrolytes), can react with different reactants and get different results, etc. Acid: a compound that produces hydrogen ions when dissolved in water.

3. 20.1 Describing Acids & Bases (cont.) Properties of Acids and Bases  Naming acids…”HX compounds”…  Add hydro- and –ic for “ide” anion compounds.  Add –ous for “ite” anion compounds.  Add –ic for “ate” anion compounds. Example: H 2 SO 4 = hydrogen sulfate…sulfuric acid. Others:  1.  2.  3.

4. 20.2 Hydrogen Ions and Acidity Hydrogen Ions from Water  Recall the polarity of a water molecule…  Sometimes the collisions between molecules are energetic enough to transfer a hydrogen ion from one molecule to another…  Figure 20.3, page 580

5. 20.2 Hydrogen Ions and Acidity (cont.) Hydrogen Ions from Water (cont.)  Self-ionization, neutral solutions, ion- product constants and acid/base solutions… Self-ionization: A reaction in which two water molecules produce ions (H 2 O H + + OH - ). Neutral solution: a solution in which the [H + ] and [OH - ] are equal.  Obviously, not all ion concentrations are equal, the solution can be described either as acidic or basic.  This can be determined by the ion- product concentration: K w = [H + ][OH - ]  [H+] < [OH-] = basic,  [H+] > [OH-] = acidic

6. 20.2 Hydrogen Ions and Acidity (cont.) The pH Concept  The measurement of this concentration can be calculated and described according to pH value, the negative log of the hydrogen-ion concentration: pH = -log[H+]  Examples…  pH 7 is basic, pH = 7 is neutral

7. Chapter 20 Assignments CPQ’s # 1 pg. 609  #34,36,37,39,41,42

8. 20.3Acid-Base Theories Arrhenius Acids and Bases  In the first part of this chapter, we defined an acid as “a compound that produces hydrogen ions when dissolved in water.” Defining an acid (or a base) is much more than that however…  Svante Arrhenius… Not all compounds containing hydrogen are acids. The number of hydrogen atoms in an acid determines how many hydrogen ions may be released:  Monoprotic, diprotic, tripotic Bronsted-Lowry Acids and Bases  Hydrogen-ion donor…hydrogen-ion acceptor  Conjugate acids and bases…

9. 20.3Acid-Base Theories (cont.) Lewis Acids and Bases  Lewis acid: a substance that can accept a pair of electrons to form a covalent bond.  Lewis base: a substance that can donate a pair of electrons to form a covalent bond. Example: H + + - O-H HOH Table 20.6, short look at acid/base theory…

10. 20.4 Strengths of Acids and Bases Strong and Weak Acids and Bases  Strong acids – completely ionized in aqueous solution… HCl, H 2 SO 4  Weak acids – ionize slightly in aqueous solution… CH 3 COOH

11. 20.4 Strengths of Acids and Bases (cont.) Strong and Weak Acids and Bases (cont.)  An acid dissociation constant (Ka) gives a more accurate representation of acid/base strength: Ka : the ratio of concentration of the dissociated form of an acid to the concentration of the undissociated form. Example: CH 3 COOH

12. Chapter 20 Assignments CPQ’s # 1 pg. 609  #34,36,37,39,41,42 CPQ’s # 2 pg. 609  #