Unit VIIChapter 15

Properties

• Both acids and bases ionize or dissociate in water

• Acids: taste sour, conduct electricity, cause certain indicators to change color, and react with metals to form H2 gas

• Bases: taste bitter, feel slippery, conduct electricity, and cause certain indicators to change color

Recognizing Acids and Bases

• Most simply, acids tend to have H’s at the beginning of their chemical formulas.

• Bases tend to have OH’s at the end of their formulas.

• NOTE: THIS IS NOT THE WHOLE TRUTH...YOU’LL LEARN MORE SOON!

Naming Acids and Bases

• REVIEW:• Binary acids• Oxyacids• Bases (named simply as ionic

compounds)• pg. 454-458

Anion Ending Acid Name

-ide hydro-(stem)-ic acid

-ate (stem)-ic acid

-ite (stem)-ous acid

Acid Nomenclature Review

Binary Binary

oxyacid oxyacid

An easy way to remember which goes with which…An easy way to remember which goes with which…

““In the cafeteria, you In the cafeteria, you ATEATE something something ICICkyky””

Practice Problems

1. HF2. HNO3

3. KOH4. H2SO4

Answers:

1. Hydrofluoric acid

2. Nitric acid

3. Potassium hydroxide

4. Sulfuric acid

Practice Problem

1. Chromic acid2. Iron (II) hydroxide3. Acetic Acid4. Lithium hydroxide

Answers:

1. H2CrO4

2. Fe(OH)2

3. CH3COOH

4. LiOH

Acid/Base Strength

• The Strength of an acid/base depends on the degree of ionization/dissociation.

• Common Aqueous Acids and Bases: Tables 15-3 and 15-4

Acid/Base Definitions

• Arrhenius Acids/Bases• Earliest and most specific definition

• Brønted-Lowry Acids/Bases• Middle definition

• Lewis Acids/Bases• Latest and most general definition

Arrhenius Acid Definition

• An acid is a compound that increases hydrogen ions [H+] concentration when dissolved in water.• Ex. HCl(g) is named hydrogen

chloride. BUT HCl(aq) is named hydrochloric

acid.

Arrhenius Base Definition

• A base is a compound that increases hydroxide ion [OH-] concentration when dissolved in water.• Ex. NaOH(s) is named sodium

hydroxide and is NOT a base. BUT NaOH (aq) is named sodium

hydroxide and IS a base.

Acidic Solutions

• An acidic solution is one in which [H3O+] is greater than [OH-].

• Ex.• HCl(g) H+ (aq) + Cl- (aq)

• Since the water is already forming some H+ ions (typically in the form of H3O+), the HCl is adding more H+ ions. This causes there to be MORE H+ or H3O+ ions than OH- ions.

H2O

Basic Solutions

• A basic solution is one in which [OH-] is greater than [H3O+].

• AKA: alkaline solutions• Ex.

• NaOH(s) Na+(aq) + OH-(aq)

• Since the water is already forming some OH- ions, NaOH is adding more OH- ions. This causes there to be MORE OH- ions than H3O+ ions.

H2O

Arrhenius Acids and Bases

• Acids are hydrogen-containing compounds that ionize to yield hydrogen ions in aqueous solution...

• Bases are compounds that ionize to yield hydroxide ions in aqueous solution...

• BUT...NH3 is a base! Arrhenius’ theory doesn’t hold up in every case, so...

Brønsted-Lowry Acids and Bases

• An acid is a hydrogen-ion donor, and a base is a hydrogen-ion acceptor.

• A substance that can either accept or donate depending upon its partner is call amphoteric.

• Example:NH3(aq) + H2O(l) NH4+(aq) + OH-(aq)

• Watch the compounds as they react. What happens across the arrow?

Practice Problem

• H2SO4 + H2O H3O+ + HSO4

-

• Label the acid, base, conjugate acid, and conjugate base.

Lewis Acid/Base Lewis Acid/Base DefinitionDefinition

Lewis acid - a Lewis acid - a substance that substance that accepts an accepts an electron pairelectron pairLewis base - a Lewis base - a substance that substance that donates an electron donates an electron pairpair

Formation ofFormation of hydronium ion hydronium ion is also is also an excellent example.an excellent example.

Lewis Acids & BasesLewis Acids & Bases

•Electron pair of the new O-H bond Electron pair of the new O-H bond originates on the Lewis base.originates on the Lewis base.

HH

H

BASE

••••••

O—HO—H

H+

ACID

Lewis Acid/Base Lewis Acid/Base ReactionReaction

Conjugate Acids and Bases

• Every acid on the left side of the reaction equation has a conjugate base on the right side of the equation.

• There is also the same base/conjugate acid pairing in each equation.

Conjugate pairs

Practice problemsPractice problemsIdentify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs:

acid base conjugate acidconjugate baseHC2H3O2(aq) + H2O(l) C2H3O2

–(aq) + H3O+(aq)

conjugate acid-base pairs

acidbase conjugate acidconjugate baseOH

–(aq) + HCO3–(aq) CO3

2–(aq) + H2O(l)

conjugate acid-base pairs

Strength of conjugates

• The stronger the acid/base, the weaker the conjugate base/acid is.

• See Table 15-6 p.471• Ex: HCl(acid)-Strong acid

Cl-(conj. base)-very weak base

Neutral Solutions

• Any aqueous solution in which [OH-] = [H3O+] is described as a neutral solution. • Ex. Pure water

• Neutralization Reactions are based on equalizing the conc. of acids and bases in solution. (Titration)