LESSON 2 pH and Buffer.pdf

Chapter 10 Acids, Bases, and Salts Chapter 10 Table of Contents 10.1 Arrhenius acid–b...

Chapter 10 Acids, Bases, and Salts Chapter 10 Table of Contents 10.1 Arrhenius acid–base theory 10.2 Brønsted–Lowry acid–base theory 10.3 Mono-, di-, and triprotic acids 10.4 Strengths of acids and bases 10.5 Ionization constants for acids and bases 10.6 Salts 10.7 Acid–base Neutralization Reactions  10.8 Self–ionization of water 10.9 The pH concept 10.10 The pKa method for expressing acid strength 10.11 The pH of aqueous salt solutions 10.12 Buffers 10.13 The Henderson–hasselbalch equation 10.14 Electrolytes 10.15 Equivalents and milliequivalents of electrolytes 10.16 Acid–base titrations Copyright ©2016 Cengage Learning. All Rights Reserved. 2 Section 10.1 Arrhenius Acid–Base Theory Arrhenius acid: Hydrogen-containing compound that produces H+ions in solution + – HNO H + NO 3 3 →  Arrhenius base: Hydroxide-containing compound that produces OH–ions in solution NaOH Na OH → ++ – Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 3 Section 10.1 Arrhenius Acid–Base Theory Ionization The process in which individual positive and negative ions are produced from a molecular compound that is dissolved in solution – Arrhenius acids Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 4 Section 10.1 Arrhenius Acid–Base Theory Dissociation  The process in which individual positive and negative ions are released from an ionic compound that is dissolved in solution – Arrhenius bases Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 5 Section 10.1 Arrhenius Acid–Base Theory  Figure 10.1 - Difference Between Ionization and Dissociation Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 6 Section 10.1 Arrhenius Acid–Base Theory Which of the following describes an Arrhenius acid and base? a. An acid is a substance that produces a hydroxide ion and a base is a substance that produces hydrogen ions in water. b. An acid is a substance that donates a hydrogen ion to another substance and a base is a substance that accepts a hydroxide ion from another substance. c. An acid is a substance that produces hydrogen ions in water and a base is a substance that produces hydroxide ions in water. d. An acid is a substance that donates a hydrogen ion to another substance and a base is a substance that accepts a hydrogen ion from another substance. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 7 Section 10.1 Arrhenius Acid–Base Theory Which of the following describes an Arrhenius acid and base? a. An acid is a substance that produces a hydroxide ion and a base is a substance that produces hydrogen ions in water. b. An acid is a substance that donates a hydrogen ion to another substance and a base is a substance that accepts a hydroxide ion from another substance. c. An acid is a substance that produces hydrogen ions in water and a base is a substance that produces hydroxide ions in water. d. An acid is a substance that donates a hydrogen ion to another substance and a base is a substance that accepts a hydrogen ion from another substance. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 8 Section 10.2 Brønsted–Lowry Acid–Base Theory Brønsted–Lowry acid: Substance that can donate a proton (H+ion) to some other substance – Proton donor Brønsted–Lowry base: Substance that can accept a proton (H+ion) from some other substance – Proton acceptor –+ HCl H O Cl + H O 23 +→ Acid Base  Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 9 Section 10.2 Brønsted–Lowry Acid–Base Theory Which of the following describes a Bronsted– Lowry acid and base? a. An acid is a substance that produces a hydroxide ion and a base is a substance that produces hydrogen ions in water. b. An acid is a substance that donates a hydrogen ion to another substance and a base is a substance that accepts a hydroxide ion from another substance. c. An acid is a substance that produces hydrogen ions in water and a base is a substance that produces hydroxide ions in water. d. An acid is a substance that donates a hydrogen ion to  another substance and a base is a substance that accepts a hydrogen ion from Return to TOC another substance. Copyright ©2016 Cengage Learning. All Rights Reserved. 10 Section 10.2 Brønsted–Lowry Acid–Base Theory Which of the following describes a Bronsted– Lowry acid and base? a. An acid is a substance that produces a hydroxide ion and a base is a substance that produces hydrogen ions in water. b. An acid is a substance that donates a hydrogen ion to another substance and a base is a substance that accepts a hydroxide ion from another substance. c. An acid is a substance that produces hydrogen ions in water and a base is a substance that produces hydroxide ions in water.  d. An acid is a substance that donates a hydrogen ion to another substance and a base is a substance that accepts a hydrogen ion from Return to TOC another substance. Copyright ©2016 Cengage Learning. All Rights Reserved. 11 Section 10.2 Brønsted–Lowry Acid–Base Theory Conjugate Acid–Base Pairs – HF( ) + H O( ) H O ( ) + F ( ) 2 3 aq l aq aq + Acid Base Conjugate Conjugate acid base  Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 12 Section 10.2 Brønsted–Lowry Acid–Base Theory Identify a conjugate acid–base pair in the following equation. HF(aq) + H2O(l) H30+(aq) + F–(aq) a. HF(aq) and H30+(aq) b. HF(aq) and F–(aq)  c. H2O(l) and F–(aq) d. HF(aq) and H2O(l) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 13 Section 10.2 Brønsted–Lowry Acid–Base Theory Identify a conjugate acid–base pair in the following equation. HF(aq) + H2O(l) H30+(aq) + F–(aq) a. HF(aq) and H30+(aq) b. HF(aq) and F–(aq)  c. H2O(l) and F–(aq) d. HF(aq) and H2O(l) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 14 Section 10.2 Brønsted–Lowry Acid–Base Theory Amphiprotic Substance A substance that can either lose or accept a proton and thus can function as either a Brønsted–Lowry acid or a Brønsted–Lowry base ‒ Example  ‒ H2O, H3O+, H2O, OH– Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 15 Section 10.3 Mono-, Di-, and Triprotic Acids Monoprotic Acid An acid that supplies one proton (H+ion) per molecule during an acid–base reaction Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 16 Section 10.3 Mono-, Di-, and Triprotic Acids Diprotic Acid An acid that supplies two protons (H+ions) per molecule during an acid–base reaction  Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 17 Section 10.3 Mono-, Di-, and Triprotic Acids Triprotic Acid An acid that supplies three protons (H+ions) per  molecule during an acid–base reaction Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 18 Section 10.3 Mono-, Di-, and Triprotic Acids Polyprotic Acid  An acid that supplies two or more protons (H+ ions) during an acid–base reaction Includes both diprotic and triprotic acids Copyright ©2016 Cengage Learning. All Rights Reserved.  Return to TOC 19 Section 10.3 Mono-, Di-, and Triprotic Acids What are the differences between a monoprotic, diprotic, and triprotic acid? a. A monoprotic acid supplies one proton per molecule; a diprotic acid supplies two protons per molecule; and a triprotic acid supplies three protons per molecule. b. A monoprotic acid supplies one proton per molecule; a diprotic acid supplies two or more protons per molecule; and a triprotic acid supplies three protons per molecule. c. A monoprotic acid supplies one hydroxide ion per molecule; a diprotic acid supplies two hydroxide ions per molecule; and a triprotic acid supplies three hydroxide ions per molecule. d. These three acids differ by the degree of ionization when  placed in a nonpolar solvent. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 20 Section 10.3 Mono-, Di-, and Triprotic Acids What are the differences between a monoprotic, diprotic, and triprotic acid? a. A monoprotic acid supplies one proton per molecule; a diprotic acid supplies two protons per molecule; and a triprotic acid supplies three protons per molecule. b. A monoprotic acid supplies one proton per molecule; a diprotic acid supplies two or more protons per molecule; and a triprotic acid supplies three protons per molecule. c. A monoprotic acid supplies one hydroxide ion per molecule; a diprotic acid supplies two hydroxide ions per molecule; and a triprotic acid supplies three hydroxide ions per molecule.  d. These three acids differ by the degree of ionization when placed in a nonpolar solvent. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 21 Section 10.4 Strengths of Acids and Bases Strong Acid Transfers ~100% of its protons to water in an aqueous solution  Equilibrium position lies far to the right Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 22 Section 10.4 Strengths of Acids and Bases Table 10.1 - Commonly Encountered Strong Acids Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 23 Section 10.4 Strengths of Acids and Bases Weak Acid Transfers only a small percent of its protons to water in an aqueous solution Equilibrium position lies far to the left Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 24 Section 10.4 Strengths of Acids and Bases Bases Strong bases - Hydroxides of Groups IA and  IIA Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 25 Section 10.8 Self-Ionization of Water An acidic solution is defined as a) An aqueous solution in which the concentration of H3O+ion is lower than that of OH–ion. b) An aqueous solution in which the concentration of H3O+ion is equal to that of OH–ion. c) An aqueous solution in which the concentration of H3O+ion is higher than that of OH–ion. d) An aqueous solution in which the concentration of OH–ion is higher than that of H3O+ion. Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 26 Section 10.9 The pH Concept  pH = –log[H3O+] A compact way to represent solution acidity pH decreases as [H+] increases pH range between 0 and 14 in aqueous solutions at 24°C Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 27 Section 10.9 The pH Concept Exercise Calculate the pH for each of the following solutions. a) 1.0 × 10–4 M H3O+ b) 0.040 M OH– Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 28 Section 10.9 The pH Concept Exercise Calculate the pH for each of the following solutions. a) 1.0 × 10–4 M H3O+ pH = 4.00 b) 0.040 M OH– pH = 12.60 Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 29 Section 10.9 The pH Concept Exercise The pH of a solution is 5.85. What is the concentration of H3O+for this solution? Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 30 Section 10.9 The pH Concept Exercise The pH of a solution is 5.85. What is the concentration of H3O+for this solution? [H3O+] = 1.4 × 10–6 M Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 31 Section 10.9 The pH Concept pH Range pH = 7; neutral  pH > 7; basic – Solutions with a higher pH are more basic pH < 7; acidic – Solutions with a lower pH are more acidic Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 32 Section 10.9 The pH Concept  Figure 10.11 - Relationships Among pH Values, [H3O+], and [OH–] Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 33 Section 10.9 The pH Concept Which of the following is the correct mathematical expression for pH? a) pH = –log [H3O+] b) pH = log [H3O+] c) pH = –log [OH–] d) pH = log [OH–] Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 34 Section 10.9 The pH Concept Which of the following is the correct mathematical expression for pH? a) pH = –log [H3O+] b) pH = log [H3O+] c) pH = –log [OH–] d) pH = log [OH–] Return to TOC  Copyright ©2016 Cengage Learning. All Rights Reserved. 35 Section 10.10 The pKa Method for Expressing Acid Strength pKa = –log Ka pKais calculated from Kain exactly the same way that pH is calculated from [H3O+] Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 36 Section 10.10 The pKa Method for Expressing Acid Strength Exercise Calculate the pKafor HF given that the Ka for this acid is 6.8 × 10–4. Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 37 Section 10.10 The pKa Method for Expressing Acid Strength Exercise  Calculate the pKafor HF given that the Ka for this acid is 6.8 × 10–4. pKa = 3.17a Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 38 Section 10.10 The pKa Method for Expressing Acid Strength pKa units is another method of expressing the strength of acids and is defined as pKa = –log Ka. If the Ka of a solution is 6.3 x 10–4, what is the pKa and is the solution acidic or basic? a. 0.80; acidic b. 0.08; basic c. 3.20; acidic d. 3.20; basic Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 39 Section 10.10 The pKa Method for Expressing Acid Strength pKa units is another method of expressing the strength of acids and is defined as pKa = –log Ka. If the Ka of a solution is 6.3 x 10–4, what is the pKa and is the solution acidic or basic? a. 0.80; acidic b. 0.08; basic c. 3.20; acidic d. 3.20; basic Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 40 Section 10.12 Buffers Key Points about Buffers Buffer: An aqueous solution containing substances that prevent major changes in solution pH when small amounts of acid or base are added to it Typically, a buffer system is composed of a weak acid and its conjugate base Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 41 Section 10.12 Buffers Buffers Contain Two Active Chemical Species 1. A substance to react with and remove added base 2. A substance to react with and remove added acid Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 42 Section 10.12 Buffers Addition of Base [OH–ion] to the Buffer The added OH–ion reacts with H3O+ion, producing water (neutralization)  The neutralization reaction produces the + stress of not enough H3O ion because H3O+ion was consumed in the neutralization The equilibrium shifts to the right to produce more H3O+ion, which maintains the pH close to its original level Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 43 Section 10.12 Buffers Addition of Acid [H3O+ion] to the Buffer  The added H3O+ion increases the overall amount of H3O+ion present The stress on the system is too much H3O+ion The equilibrium shifts to the left consuming most of the excess H3O+ion and resulting in a pH close to the original level Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 44 Section 10.12 Buffers What two active species are contained in a buffer? a. A substance that resists changes in pH when a small amount of base is added b. A substance that resists changes in pH when a small amount of acid is added c. A weak acid and its conjugate base d. All of these Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 45 Section 10.12 Buffers What two active species are contained in a buffer? a. A substance that resists changes in pH when a small amount of base is added. b. A substance that resists changes in pH when a small amount of acid is added. c. A weak acid and its conjugate base. d. All of these Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 46 Section 10.13 The Henderson–Hasselbalch Equation Henderson–Hasselbalch Equation ⎡⎤⎣⎦ K pH = log A p+ − a  HA Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. [] 47 Section 10.13 The Henderson–Hasselbalch Equation Exercise What is the pH of a buffer solution that is 0.45  M acetic acid (HC2H3O2) and 0.85 M sodium acetate (NaC2H3O2)? The Kafor acetic acid is 1.8 × 10–5. pH = 5.02 Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 48 Section 10.13 The Henderson–Hasselbalch Equation What is the mathematical expression for the Henderson–Hasselbach equation? a. pH = pKa + log [A–]/[HA] b. pH = pKa + log [Base]/[Acid] c. pH = pKa + log [HA]/[A–] d. Both (a) and (b) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 49 Section 10.13 The Henderson–Hasselbalch Equation What is the mathematical expression for the Henderson–Hasselbach equation? a. pH = pKa + log [A–]/[HA] b. pH = pKa + log [Base]/[Acid] c. pH = pKa + log [HA]/[A–] d. Both (a) and (b) Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 50 Section 10.14 Electrolytes  Acids, bases, and soluble salts all produce ions in solution; thus they all produce solutions that conduct electricity Electrolyte: Substance whose aqueous solution conducts electricity Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 51 Section 10.14 Electrolytes Nonelectrolytes They do not conduct electricity Example - Table sugar (sucrose) and glucose Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 52 Section 10.14 Electrolytes Strong Electrolytes  They completely ionize/dissociate into ions Example - Strong acids, bases, and soluble salts Copyright ©2016 Cengage Learning. All Rights Reserved. Return to TOC 53 Section 10.14 Electrolytes Weak Electrolytes  They incompletely ionize/dissociate into ions Example - Weak acids and bases Copyright ©2016 Cengage Learning. All Rights Reserved.  Return to TOC 54 Section 10.14 Electrolytes What is an electrolyte?  a. A substance that completely dissociates or ionizes when placed in water b. A substance that incompletely dissociates or ionizes when placed in water c. A substance whose aqueous solution conducts electricity d. All of these Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 55 Section 10.14 Electrolytes What is an electrolyte? a. A substance that completely dissociates or ionizes when placed in water b. A substance that incompletely dissociates or ionizes when placed in water c. A substance whose aqueous solution conducts electricity d. All of these Return to TOC Copyright ©2016 Cengage Learning. All Rights Reserved. 56