Chemistry 140

Chapter 9

“Acids and Bases”

CHAPTER OUTLINE

9.1 The Arrhenius Theory 9.2 The Brønsted Theory 9.3 Naming Acids 9.4 The Self‐Ionization of Water 9.5 The pH Concept 9.6 Properties of Acids 9.7 Properties of Bases 9.8 Salts 9.9 The Strengths of Acids and Bases 9.10 Analyzing Acids and Bases 9.11 Titration Calculations 9.12 Hydrolysis Reactions of Salts 9.13 Buffers

LEARNING OBJECTIVES/ASSESSMENT

When you have completed your study of this chapter, you should be able to: 1. Write reaction equations that illustrate Arrhenius acid‐base behavior. (Section 9.1; Exercise 9.2) 2. Write reaction equations that illustrate Brønsted acid‐base behavior, and identify Brønsted acids and bases from

written reaction equations. (Section 9.2; Exercises 9.6 and 9.10) 3. Name common acids. (Section 9.3; Exercise 9.22) 4. Do calculations using the concept of the self‐ionization of water. (Section 9.4; Exercises 9.28 a & b, and 9.30 a &

b) 5. Do calculations using the pH concept. (Section 9.5; Exercises 9.36 and 9.40) 6. Write reaction equations that illustrate the characteristic reactions of acids. (Section 9.6; Exercise 9.50) 7. Write reaction equations that represent neutralization reactions between acids and bases. (Section 9.7; Exercise 9.60) 8. Write reaction equations that illustrate various ways to prepare salts, and do calculations using the concept of an

equivalent of salt. (Section 9.8; Exercises 9.68 and 9.74) 9. Demonstrate an understanding of the words weak and strong as applied to acids and bases. (Section 9.9; Exercise

9.86) 10. Demonstrate an understanding of the titration technique used to analyze acids and bases. (Section 9.10;

Exercise 9.92) 11. Do calculations related to the analysis of acids and bases by titration. (Section 9.11; Exercises 9.98 and 9.100 a) 12. Explain the concept of salt hydrolysis, and write equations to illustrate the concept. (Section 9.12; Exercise

9.108) 13. Explain how buffers work, and write equations to illustrate their action. (Section 9.13; Exercise 9.116)

Acids and Bases

Acids, bases, and salts are electrolytes, substances whose water solutions conduct electricity.

They are uniquely related in that acids react with bases to produce salts and water.

The word salt is a derivative of the Latin word sal which means vital compound.

Roman soldiers were paid with salt, sal-ary. Salt has long been used to flavor and preserve food and as medicine.

The Nature of Acids

Acids are present in many foods, especially fruit. All foods which taste sour have some type of acid in them. Some organic acids include;

ACID FOOD citric acid lemons malic acid apples lactic acid milk butyric acid rancid butter acetic acid vinegar

Industrial Acids

1. sulfuric acid a. formula - H2SO4

b. dense c. oily d. high boiling point e. concentrated - 95% f. diluted - 1 part acid, 6 parts water g. uses - car batteries, refining petroleum

Industrial Acids (continued)

2. nitric acid a. formula - HNO3

b. unstable (volatile) in pure form c. concentrated - 70% d. diluted - 1 part acid, 5 parts water e. turns yellow in light f. uses - fertilizers, explosives

Industrial Acids (continued)

3. hydrochloric acid a. formula - HCl b. gaseous HCl, extremely soluble in water c. concentrated - 36% d. diluted - 1 part acid, 4 parts water e. uses - steel manufacturing, stomach acid

Aqueous Acids

Acids do not display characteristic properties unless they are in water solution. The definition of an electrolyte indicates the necessity of the substance being in a water solution. NEVER ADD WATER TO AN ACID!! Remember this phrase, "do what you oughta, pour the acid in the watta!" The following equations demonstrate ion formation as acids are added to water.

1. Ionization of H2SO4

Properties of Acids 1. Acids donate protons in the presence of bases. HCl monoprotic H2SO4 diprotic H+ Cl- + Na+OH- ® Na+Cl- + H+OH-

2. Acids contain ionizable hydrogen covalently bonded to a nonmetallic element or polyatomic species.

nonmetal......................HCl polyatomic species...H3PO4

Properties of Acids (continued)

3. Acids taste sour. NEVER USE THE TASTE TEST!!!

4. Acids affect indicators. litmus turns red phenolphthalein remains clear methyl orange turns red 5. Acids neutralize hydroxides. HCl + NaOH ® NaCl + H2O

Properties of Acids (continued)

6. Acids react with many metals. Zn(s) + H2SO4(aq) ® ZnSO4(aq) + H2(g) 7. Acids react with oxides of metals. CuO + H2SO4 ® CuSO4 + H2O 8. Acids react with carbonates. CaCO3 + 2HCl ® CaCl2 + H2O + CO2

Naming Aqueous Acids 1. Binary Acids a. prefix “hydro” b. root word c. suffix "ic" Examples: FORMULA NAME HCl ___________________________ HBr ___________________________ H2S ___________________________

H2Se ___________________________ HI ___________________________

Oxyacids a. prefix i. “hypo” for ions having one less oxygen than the

“ite” ion ii. no prefix for the “ite” ion iii. no prefix for the “ate” ion iv. “per” for ions having one more oxygen than the

“ate” ion b. root name c. suffix i. “ous” for the “ite” ion ii. “ic” for the “ate” ion

Oxyacids Containing Halogens Traditionally, an "X" is used to denote the

halogens. The following generalization applies. HXO4 per - root name - ic

HXO3 root name - ic

HXO2 root name - ous HXO hypo - root name -

ous

Examples FORMULA NAME H2SO4 ____________________________

H2SO3 ____________________________

HNO3 ____________________________

HClO3 ____________________________

HClO2 ____________________________ HClO ____________________________ HClO4 ____________________________

Acid Anhydrides Acid anhydrides are oxides which react with

water to form acids. To determine an acid anhydride, simply subtract water from the acid in question. Anhydride means without water.

Examples: ACID ACID ANHYDRIDE H2SO4 ________________

H3PO4 ________________

H2CO3 ________________

Name the following acids and find the acid anhydride where applicable.

FORMULA NAME ANHYDRIDE

H2Te _______________

HNO3 _______________

H3PO4 _______________ __________

H2SeO3 _______________ __________

H3PO3 _______________ __________

H2CO2 _______________ __________

HC2H3O2 ______________

Bases Bases are often referred to as hydroxides. The

hydroxide ion, OH-, is responsible for most basic or alkaline properties. The basicity of a substance is also referred to as the alkalinity.

Name some common household bases. 1. lye 4. soap 2. lime 5. antacids 3. laxatives 6. eggs base - a proton acceptor

Properties of Hydroxides 1. Hydroxides of active metals supply hydroxide

ions, OH-. Na+OH- ® Na+(aq) + OH-(aq) 2. Soluble hydroxides have a bitter taste. NEVER

USE THE TASTE TEST!! 3. Solutions of hydroxides feel slippery. 4. Soluble hydroxides affect indicators. red litmus paper turns blue phenolphthalein turns red methyl orange turns yellow

Properties of Hydroxides (continued)

5. Hydroxides neutralize acids. NaOH + HCl ® NaCl + H2O 6. Hydroxides react with oxides of nonmetals. CO2 + 2NaOH ® Na2CO3 + H2O 7. Certain hydroxides are amphoteric; i.e., they

take on acid properties in the presence of stronger bases and take on basic properties in the presence of strong acids.

Example: Write the formula for aluminum hydroxide which shows acidic properties.

Basic Anhydrides Oxides which react with water to form solutions

containing the hydroxide ion are basic anhydrides.

Find the base anhydride of each of the following. FORMULA ANHYDRIDE Ca(OH)2 ____________

Mg(OH)2 ____________

Ba(OH)2 ____________

Al(OH)3 ____________

Conjugate Acids and Conjugate Bases A conjugate base is the species which remains after

an acid has given up a proton. A conjugate acid is the species formed when a base takes on a proton. Given the following reaction, complete the reaction equation and identify the conjugate base of sulfuric acid. Also identify the remaining conjugate acid, the reacting acid and reacting base.

H2SO4 + H2O ® Notice: The stronger an acid, the weaker its

conjugate base, the stronger a base, the weaker its conjugate acid.

Practice: For each of the following, write the ionic equation, identify the acid, base, conjugate acid, and

conjugate base.

1. hydrochloric acid + water ®

2. sulfurous acid + water ®

3. phosphoric acid + water ®

4. acetic acid + water ®

Salts A salt is a compound composed of the positive

ion of an aqueous base and the negative ion of an aqueous acid.

We usually think of table salt, NaCl, when we hear the word salt. There are actually many kinds of salts.

Our bodies obtain minerals in the form of salts. For example, with your knowledge of the active metal sodium, what would happen if you tried to eat pure sodium metal?

Eating NaCl is much safer!

Salt-Producing Reactions 1. Direct union of elements. 2Na + Cl2 ® 2NaCl 2. Reaction of a metal with an acid. Zn + 2HCl ® ZnCl2 + H2

3. Reaction of metallic oxide with an aqueous acid.

MgO + 2HCl ® MgCl2 + H2O 4. Reaction of a nonmetallic oxide with a base. CO2 + Ca(OH)2 ® CaCO3 + H2O

Salt-Producing Reactions (continued)

5. Acid-base neutralization. NaOH + HCl ® NaCl + H2O 6. Ionic reaction. BaCl2 + Na2SO4 ® 2NaCl + BaSO4

7. Reaction of an acid with a carbonate. 2HCl + Na2CO3 ® 2NaCl + H2O + CO2

8. Reaction of a metallic oxide with a nonmetallic oxide.

MgO + CO2 ® MgCO3

Naming Salts Most compounds which we have learned to

name are salts. For each of the following, name the compound and indicate "A" for acid, "B" for base, or "S" for salt.

FORMULA NAME TYPE H2CO3___________________________ _____

Ba(OH)2__________________________ _____

CuSO4___________________________ _____