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

Objectives Objectives  Define the properties of acids and bases.  Compare and contrast acids and bases as defined by the theories of Arrhenius, Br Ø nsted- 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 [H 3 O + ] in an aqueous solution  Arrhenius base: compound that increases hydroxide ion concentration [OH - ] in an aqueous solution  Br Ø nsted-Lowry acid: hydrogen ion (H + ) donor  Br Ø nsted-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 [H 3 O + ]: HCl (aq) + H 2 O(l)  H 3 O + (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 (HNO 3 ), are called monoprotic acids.  Acids that contain two ionizable hydrogens, such as sulfuric acid (H 2 SO 4 ), are called diprotic acids.  Acids that contain three ionizable hydrogens, such as phosphoric acid (H 3 PO 4 ) 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 H 2 SO 4 is an Acid A water molecule that accepts a hydrogen ion becomes a positively charged hydronium ion (H 3 O + ) and the H 2 SO 4 gives up a hydrogen ion and becomes a negatively charged hydrogen sulfate ion (HSO 4 - ).

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. H 2 O is donating the electrons and H + is accepting the electrons b. AlCl 3 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? a)taste sour b)are electrolytes c)feel slippery d)affect the color of indicators

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

2. Which compound is most likely to act as an Arrhenius acid? a)H 2 O b)NH 3 c)NaOH d)H 2 SO 4

2. Which compound is most likely to act as an Arrhenius acid? a)H 2 O b)NH 3 c)NaOH d)H 2 SO 4

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

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