Unit 9Acid-Base Chemistry

Chapters 14 & 15

ACIDS & BASESChapter 14

Properties of Acids

• Taste sour.• React with metals to

release H2 gas.

• React with bases to produce salts and water.

• Change the color of acid-base indicators.

• Conduct electric current.

Chapter 14 – Section 1: Properties of Acids and Bases

Properties of Bases

• Taste bitter.• Feel slippery.• React with acids to

produce salts and water.• Change the color of

acid-base indicators.• Conduct electric current.

Chapter 14 – Section 1: Properties of Acids and Bases

Arrhenius Acids and Bases

• An Arrhenius acid produces hydrogen ions, H+, in aqueous solution.• An Arrhenius base produces hydroxide ions, OH−, in aqueous solution.• A strong acid (or base) ionizes completely.• A weak acid (or base) releases only a few ions.

Chapter 14 – Section 1: Properties of Acids and Bases

Brønsted-Lowry Acids and Bases

• A Brønsted-Lowry acid is a molecule or ion that is a proton donor.• A Brønsted-Lowry base is a molecule or ion that is a proton acceptor.

Example:–Hydrogen chloride acts as a Brønsted-Lowry acid when it reacts with ammonia.

–Ammonia accepts a proton from the hydrochloric acid. It acts as a Brønsted-Lowry base.

Chapter 14 – Section 2: Acid-Base Theories

+ –3 4HCl NH NH Cl

Lewis Acids and Bases

• A Lewis acid is an atom, ion, or molecule that accepts an electron pair to form a covalent bond.

• A Lewis base is an atom, ion, or molecule that donates an electron pair to form a covalent bond.

• The Lewis definition is the broadest of the three definitions.

Chapter 14 – Section 2: Acid-Base Theories

Comparing the Three Definitions

• Comparison Chart (from Page 482)

Visual Concept

Chapter 14 – Section 2: Acid-Base Theories

Amphoteric Compounds

• An amphoteric substance is one that can react as either an acid or a base.

Example: water•water can act as an acid.

•Water can act as a base.

Chapter 14 – Section 3: Acid-Base Reactions

g + l aq aq–3 2 4NH ( ) H O( ) NH ( ) OH ( )

base acid

aq + l aq + aq–2 4 2 3 4H SO ( ) H O( ) H O ( ) HSO ( )

acid base

Visual Concept

pHChapter 15

The pH Scale• pH is defined as the negative of the

common logarithm of the hydronium ion concentration.

pH = −log [H3O+]

Example: a neutral solution has a [H3O+] = 1×10−7

The logarithm of 1×10−7 is −7.0. pH = −log [H3O+] = −log(1 × 10−7) = −

(−7.0) = 7.0

Chapter 15 – Section 1: Aqueous Solutions and the Concept of pH

The pH Scale (continued)

Chapter 15 – Section 1: Aqueous Solutions and the Concept of pH

The pH ScaleSample Problem

Identify each of the following solutions as acidic, basic, or neutral:a.) [H3O+] = 1.0 x 10-7

b.) pH = 13.0

c.) [H3O+] = 1.0 x 10-5

d.) pH = 1.0

Chapter 15 – Section 1: Aqueous Solutions and the Concept of pH

pH = 7 neutral

basic

pH = 5 acidic

acidic

The pOH Scale• pOH is defined as the negative of the

common logarithm of the hydroxide ion concentration.

pH = −log [OH-]

Example: a basic solution has a [OH-] = 1×10−3

The logarithm of 1×10−3 is −3.0. pOH = −log [OH-] = −log(1 × 10−3) = −(−3.0)

= 3.0

Chapter 15 – Section 1: Aqueous Solutions and the Concept of pH

Comparing pH and pOH

• The sum of the pH and pOH of a solution is 14.

pH + pOH = 14.0

Chapter 15 – Section 1: Aqueous Solutions and the Concept of pH

pH and pOHSample Problem

An aqueous solution has a pH of 4.0. Determine:a.) The hydronium ion concentration.

b.) The hydroxide ion concentration.

Chapter 15 – Section 1: Aqueous Solutions and the Concept of pH

[H3O+] =

1.0 x 10-

4

pOH = 14.0 - pH

= 14.0 – 4.0 pOH =

10.0[OH-] =1.0 x 10-

10