Prentice-Hall Chapter 19.1 Dr. Yager Acid-Base Theories Prentice-Hall Chapter 19.1 Dr. Yager

Objectives Define the properties of acids and bases. Compare and contrast acids and bases as defined by the theories of Arrhenius, BrØnsted-Lowry, and Lewis.

Properties of Acids Acids taste sour, will change the color of an acid-base indicator, and can be strong or weak electrolytes in aqueous solution. Citrus fruits contain citric acid. Tea contains tannic acid.

Properties of a Base Bases taste bitter, feel slippery, will change the color of an acid-base indicator, and can be strong or weak electrolytes in aqueous solution. Antacids neutralize stomach acid. Ca(OH)2 is used in mortar.

Definitions of Acids and Bases Arrhenius acid: hydrogen containing compound that increases hydronium ion concentration [H3O+] in an aqueous solution Arrhenius base: compound that increases hydroxide ion concentration [OH-] in an aqueous solution BrØnsted-Lowry acid: hydrogen ion (H+) donor BrØnsted-Lowry base: hydrogen ion acceptor Lewis acid/base: electron-pair acceptor/donor

Arrhenius Acids and Bases Arrhenius acids are hydrogen-containing compounds that ionize to yield hydrogen ions (H+) in aqueous solution, thus also increasing hydronium ion concentration [H3O+]: HCl (aq) + H2O(l)  H3O+ (aq) + Cl- (aq) Arrhenius bases are compounds that ionize to yield hydroxide ions (OH–) in aqueous solution. NaOH (aq)  Na+ (aq) + OH- (aq) Most common understanding of acids and bases

Hydrochloric Acid

Arrhenius Acids Acids that contain one ionizable hydrogen, such as nitric acid (HNO3), are called monoprotic acids. Acids that contain two ionizable hydrogens, such as sulfuric acid (H2SO4), are called diprotic acids. Acids that contain three ionizable hydrogens, such as phosphoric acid (H3PO4) are called triprotic acids.

Arrhenius Base Hydroxide ions are one of the products of the dissolution of an alkali metal in water.

Arrhenius Base

Milk of magnesia is a base used as an antacid.

Brønsted-Lowry Acids and Bases The Brønsted-Lowry theory defines an acid as a hydrogen-ion donor, and a base as a hydrogen-ion acceptor.

Why Ammonia is a Base

Conjugate Acids and Bases A conjugate acid is the particle formed when a base gains a hydrogen ion. A conjugate base is the particle that remains when an acid has donated a hydrogen ion.

Conjugate Acids and Bases A conjugate acid-base pair consists of two substances related by the loss or gain of a single hydrogen ion. A substance that can act as both an acid and a base is said to be amphoteric.

Why H2SO4 is an Acid A water molecule that accepts a hydrogen ion becomes a positively charged hydronium ion (H3O+) and the H2SO4 gives up a hydrogen ion and becomes a negatively charged hydrogen sulfate ion (HSO4-).

Lewis Acids and Bases Lewis proposed that an acid accepts a pair of electrons during a reaction, while a base donates a pair of electrons.

Lewis Acids and Bases A Lewis acid is a substance that can accept a pair of electrons to form a covalent bond. A Lewis base is a substance that can donate a pair of electrons to form a covalent bond.

a. H2O is donating the electrons and H+ is accepting the electrons b. AlCl3 is accepting the electrons and Cl- is donating the electrons

Theories in Order of Discovery

1. Which of the following is NOT a characteristic of acids? taste sour are electrolytes feel slippery affect the color of indicators

1. Which of the following is NOT a characteristic of acids? taste sour are electrolytes feel slippery affect the color of indicators

2. Which compound is most likely to act as an Arrhenius acid? H2O NH3 NaOH H2SO4

2. Which compound is most likely to act as an Arrhenius acid? H2O NH3 NaOH H2SO4

3. A Lewis acid is any substance that can accept a hydronium ion. a proton. hydrogen. a pair of electrons.

3. A Lewis acid is any substance that can accept a hydronium ion. a proton. hydrogen. a pair of electrons.