5/10/2017. Chapter 10. Acids, Bases, and Salts

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1 Chapter 10. Acids, Bases, and Salts Introduction to Inorganic Chemistry Instructor Dr. Upali Siriwardane (Ph.D. Ohio State) Office: 311 Carson Taylor Hall ; Phone: ; Office Hours: MWF 8:00-9:00 and 11:00-12:00; TR 10:00-12:00 Contact me trough phone or if you have questions Online Tests on Following days March 24, 2017: Test 1 (Chapters 1-3) April 10, 2017 : Test 2 (Chapters 4-5) May 1, 2017: Test 3 (Chapters 6,7 &8) May 12, 2017 : Test 4 (Chapters 9, 10 &11) May 15, 2017: Make Up Exam: Chapters 1-11). Chapter 10 Table of Contents 10.1 Arrhenius Acid-Base Theory 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 The pka Method for Expressing Acid Strength The Henderson-Hasselbalch Equation Electrolytes Equivalents and Milliequivalents of Electrolytes Acid-Base Titrations Copyright Cengage Learning. All rights reserved 2 Section 10.1 Arrhenius Acid-Base Theory Arrhenius acid: hydrogen-containing compound that produces H + ions in solution. Example: HNO 3 H + + NO 3 Arrhenius base: hydroxide-containing compound that produces OH ions in solution. Example: NaOH Na + + OH 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 Example: HCl H + + Cl Copyright Cengage Learning. All rights reserved 3 Copyright Cengage Learning. All rights reserved 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 Example: KOH K + + OH Section 10.1 Arrhenius Acid-Base Theory Difference Between Ionization and Dissociation Copyright Cengage Learning. All rights reserved 5 Copyright Cengage Learning. All rights reserved 6 1

2 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 2 O Cl + H 3 O + acid base Brønsted-Lowry Reaction To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright Cengage Learning. All rights reserved 7 Copyright Cengage Learning. All rights reserved 8 Acid in Water Acid dissociation Equilibrium HA(aq) + H 2 O(l) H 3 O + (aq) + A - (aq) acid base conjugate conjugate acid base HC 2 H 3 O 2 (aq) + H 2 O(l) H 3+ O(aq) + C 2 H 3 O 2- (aq) [H + ][C 2 H 3 O 2- ] HC 2 H 3 O 2 ; K a = [HC 2 H 3 O 2 ] Copyright Cengage Learning. All rights reserved 9 Copyright Cengage Learning. All rights reserved 10 Base dissociation Equilibrium Acid Ionization Equilibrium NH 3 (aq) + H 2 O(l) NH 4+ (aq) + OH - (aq) [NH 4+ ][OH - ] NH 3 ; K b = [NH 3 ] To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright Cengage Learning. All rights reserved 11 Copyright Cengage Learning. All rights reserved 12 2

3 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: H 2 O, H 3 O + H 2 O, OH 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. HA + H 2 O A + H 3 O + Copyright Cengage Learning. All rights reserved 13 Copyright Cengage Learning. All rights reserved 14 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. H 2 A + H 2 O HA + H 3 O + ; K a1 HA + H 2 O A 2 + H 3 O + ; K a2 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. H 3 A + H 2 O H 2 A + H 3 O + ; K a1 H 2 A + H 2 O HA 2 + H 3 O + ; K a2 HA 2 + H 2 O A 3 + H 3 O + ; K a3 Copyright Cengage Learning. All rights reserved 15 Copyright Cengage Learning. All rights reserved 16 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. Section 10.4 Strengths of Acids and Bases Differences Between Strong and Weak Acids in Terms of Species Present Copyright Cengage Learning. All rights reserved 17 Copyright Cengage Learning. All rights reserved 18 3

4 Section 10.4 Strengths of Acids and Bases Strong Acid Transfers ~100% of its protons to water in an aqueous solution. (aq) HCl + H 2 O H 3 O + (aq) + Cl (aq) Ionization equilibrium lies far to the right (product). Yields a weak conjugate base Cl - ion. Section 10.4 Strengths of Acids and Bases Commonly Encountered Strong Acids Copyright Cengage Learning. All rights reserved 19 Copyright Cengage Learning. All rights reserved 20 Section 10.4 Strengths of Acids and Bases Weak Acid Transfers ~small % of its protons to water in an aqueous solution. HC 2 H 3 O 2 (aq) + H 2 O(l) H 3 +O(aq) + C 2 H 3 O 2 -(aq) weak Acid conjugate base Ionization equilibrium lies far to the left (reactant). Yields a strong conjugate base C 2 H 3 O 2 - ion. Section 10.4 Strengths of Acids and Bases Bases Strong bases: hydroxides of Groups IA and IIA. Copyright Cengage Learning. All rights reserved 21 Copyright Cengage Learning. All rights reserved 22 Section 10.5 Ionization Constants for Acids and Bases Acid Ionization Constant The equilibrium constant for the reaction of a weak acid with water. HA(aq) + H 2 O(l) K a + - éh3o ù éa ù = ë û ë û H 3 O + (aq) + A - (aq) [ HA] Section 10.5 Ionization Constants for Acids and Bases Acid Strength, % Ionization, and K a Magnitude Acid strength increases as % ionization increases. Acid strength increases as the magnitude of K a increases. % Ionization increases as the magnitude of K a increases. Copyright Cengage Learning. All rights reserved 23 Copyright Cengage Learning. All rights reserved 24 4

5 Section 10.5 Ionization Constants for Acids and Bases Base Ionization Constant The equilibrium constant for the reaction of a weak base with water. B(aq) + H 2 O(l) K b BH + (aq) + OH (aq) + - ébh ù éoh ù = ë û ë û [ B] Section 10.6 Salts Ionic compounds containing a metal or polyatomic ion as the positive ion and a nonmetal or polyatomic ion (except hydroxide) as the negative ion. x NaCl, NH 4 Cl, NaSO 4 NaOH All common soluble salts are completely dissociated into ions in aqueous solution. NaCl + H 2 O(l) Na + (aq) + Cl (aq), Copyright Cengage Learning. All rights reserved 25 Copyright Cengage Learning. All rights reserved 26 Section 10.7 Acid-Base Neutralization Reactions Neutralization Reaction The chemical reaction between an acid and a hydroxide base in which a salt and water are the products. Acid + Base Salt + water Section 10.7 Acid-Base Neutralization Reactions Formation of Water HCl + NaOH NaCl + H 2 O H 2 SO KOH K 2 SO H 2 O Copyright Cengage Learning. All rights reserved 27 Copyright Cengage Learning. All rights reserved 28 Self-Ionization (Auto-Ionization) Water molecules in pure water interact with one another to form ions. [H 3 O + ] = 1x x 10-7 H 2 O + H 2 O H 3 O + + OH Net effect is the formation of equal amounts of hydronium and hydroxide ions. Ionic Product H 2 O; K w = [H 3 O + ][OH ] = Copyright Cengage Learning. All rights reserved 29 Copyright Cengage Learning. All rights reserved 30 5

6 Ion Product Constant for Water At 24 C: K w = [H 3 O + ][OH ] = No matter what the solution contains, the product of [H 3 O + ] and [OH ] must always equal Relationship Between [H 3 O + ] and [OH ] Copyright Cengage Learning. All rights reserved 31 Copyright Cengage Learning. All rights reserved 32 Three Possible Situations [H 3 O + ] = [OH ]; neutral solution [H 3 O + ] > [OH ]; acidic solution [H 3 O + ] < [OH ]; basic solution Calculate [H 3 O + ] or [OH ] as required for each of the following solutions at 24 C, and state whether the solution is neutral, acidic, or basic. a) M OH b) 2.0 M H 3 O + Copyright Cengage Learning. All rights reserved 33 Copyright Cengage Learning. All rights reserved 34 Calculate [H 3 O + ] or [OH ] as required for each of the following solutions at 24 C, and state whether the solution is neutral, acidic, or basic. a) M OH M H 3 O + ; basic b) 2.0 M H 3 O M OH ; acidic ph = log[h 3 O + ] A compact way to represent solution acidity. ph decreases as [H + ] increases. ph range between 0 to 14 in aqueous solutions at 24 C. Copyright Cengage Learning. All rights reserved 35 Copyright Cengage Learning. All rights reserved 36 6

7 Calculate the ph for each of the following solutions. Calculate the ph for each of the following solutions. a) M H 3 O + b)0.040 M OH a) M H 3 O + ph = 4.00 b)0.040 M OH ph = Copyright Cengage Learning. All rights reserved 37 Copyright Cengage Learning. All rights reserved 38 The ph of a solution is What is the [H 3 O + ] for this solution? The ph of a solution is What is the [H 3 O + ] for this solution? [H 3 O + ] = M Copyright Cengage Learning. All rights reserved 39 Copyright Cengage Learning. All rights reserved 40 ph Range ph = 7; neutral ph > 7; basic Higher the ph, more basic. ph < 7; acidic Lower the ph, more acidic. Relationships Among ph Values, [H 3 O + ], and [OH ] Copyright Cengage Learning. All rights reserved 41 Copyright Cengage Learning. All rights reserved 42 7

8 Section The pk a Method for Expressing Acid Strength pk a = log K a pk a is calculated from K a in exactly the same way that ph is calculated from [H 3 O + ]. Section The pk a Method for Expressing Acid Strength Calculate the pk a for HF given that the K a for this acid is Copyright Cengage Learning. All rights reserved 43 Copyright Cengage Learning. All rights reserved 44 Section The pk a Method for Expressing Acid Strength Calculate the pk a for HF given that the K a for this acid is pk a = 3.17a Salts Ionic compounds. When dissolved in water, break up into its ions (which can behave as acids or bases). Hydrolysis the reaction of a salt ions with water to produce hydronium ion or hydroxide ion or both. NH 4 + Cl - NH 4 + Conjugate acid of weak base NH 4+ + H 2 O NH 3 + H 3 O + Copyright Cengage Learning. All rights reserved 45 Copyright Cengage Learning. All rights reserved 46 Types of Salt Hydrolysis 1. The salt of a strong acid and a strong base does not hydrolyze, so the solution is neutral. KCl, NaNO 3 Types of Salt Hydrolysis 2. The salt of a strong acid and a weak base hydrolyzes to produce an acidic solution. NH 4 Cl NH 4+ + H 2 O NH 3 + H 3 O + Copyright Cengage Learning. All rights reserved 47 Copyright Cengage Learning. All rights reserved 48 8

9 Types of Salt Hydrolysis 3. The salt of a weak acid and a strong base hydrolyzes to produce a basic solution. NaF, F + H 2 O HF + OH F Conjugate base of weak acid KC 2 H 3 O 2 C 2 H 3 O 2 + H 2 O HC 2 H 3 O 2 + OH C 2 H 3 O 2 Conjugate acid of weak acid Types of Salt Hydrolysis 4. The salt of a weak acid and a weak base hydrolyzes to produce a slightly acidic, neutral, or slightly basic solution, depending on the relative weaknesses of the acid and base. Copyright Cengage Learning. All rights reserved 49 Copyright Cengage Learning. All rights reserved 50 Neutralization Parentage of Salts Neutralization Parentage of Salts Copyright Cengage Learning. All rights reserved 51 Copyright Cengage Learning. All rights reserved 52 What salt solutions would be acidic, basic and neutral? 1) strong acid + strong base = neutral 2) weak acid + strong base = basic 3) strong acid + weak base = acidic 4) weak acid + weak base = neutral, basic or an acidic solution depending on the relative strengths of the acid and the base. Section Key Points about Buffer an aqueous solution containing substances that prevent major changes in solution ph when small amounts of acid or base are added to it. They are weak acids or bases containing a common ion. Typically, a buffer system is composed of a weak acid and its conjugate base. Copyright Cengage Learning. All rights reserved 54 9

10 Section 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. Section Adding an Acid to a Buffer Copyright Cengage Learning. All rights reserved 55 To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright Cengage Learning. All rights reserved 56 Section To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Copyright Cengage Learning. All rights reserved 57 Section Addition of Base [OH ion] to the Buffer HA + H 2 O H 3 O + + A The added OH ion reacts with H 3 O + ion, producing water (neutralization). The neutralization reaction produces the stress of not enough H 3 O + ion because H 3 O + ion was consumed in the neutralization. The equilibrium shifts to the right to produce more H 3 O + ion, which maintains the ph close to its original level. Copyright Cengage Learning. All rights reserved 58 Section Addition of Acid [H 3 O + ion] to the Buffer HA + H 2 O H 3 O + + A The added H 3 O + ion increases the overall amount of H 3 O + ion present. The stress on the system is too much H 3 O + ion. The equilibrium shifts to the left consuming most of the excess H 3 O + ion and resulting in a ph close to the original level. Section The Henderson-Hasselbalch Equation Henderson-Hasselbalch Equation éë A ùû ph = p Ka + log HĀ [ ] Copyright Cengage Learning. All rights reserved 59 Copyright Cengage Learning. All rights reserved 60 10

11 Section The Henderson-Hasselbalch Equation What is the ph of a buffer solution that is 0.45 M acetic acid (HC 2 H 3 O 2 ) and 0.85 M sodium acetate (NaC 2 H 3 O 2 )? The K a for acetic acid is Section 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. ph = 5.02 Copyright Cengage Learning. All rights reserved 61 Copyright Cengage Learning. All rights reserved 62 Section Electrolytes Nonelectrolyte does not conduct electricity Example: table sugar (sucrose), glucose Section Electrolytes Strong Electrolyte completely ionizes/dissociates Example: strong acids, bases, and soluble salts Copyright Cengage Learning. All rights reserved 63 Copyright Cengage Learning. All rights reserved 64 Section Electrolytes Weak Electrolyte incompletely ionizes/dissociates Example: weak acids and bases Section Equivalents and Milliequivalents of Electrolytes Equivalent (Eq) of an Ion The molar amount of that ion needed to supply one mole of positive or negative charge. 1 mole K + = 1 equivalent 1 mole Mg 2+ = 2 equivalents 1 mole PO 4 3 = 3 equivalents Copyright Cengage Learning. All rights reserved 65 Copyright Cengage Learning. All rights reserved 66 11

12 Section Equivalents and Milliequivalents of Electrolytes Milliequivalent Section Equivalents and Milliequivalents of Electrolytes Concentrations of Major Electrolytes in Blood Plasma 1 milliequivalent = 10 3 equivalent Copyright Cengage Learning. All rights reserved 67 Copyright Cengage Learning. All rights reserved 68 Section Equivalents and Milliequivalents of Electrolytes Section Equivalents and Milliequivalents of Electrolytes The concentration of Ca 2+ ion present in a sample is 5.3 meq/l. How many milligrams of Ca 2+ ion are present in ml of the sample? The concentration of Ca 2+ ion present in a sample is 5.3 meq/l. How many milligrams of Ca 2+ ion are present in ml of the sample? 19 mg Ca 2+ ion L 5.3 meq 1 Eq 1 mol Ca g Ca 1000 mg ( )( )( )( )( 2+ )( 2+ )( ) 1000 ml 1 L 1000 meq 2 Eq Ca 1 mol Ca 1 g ml = 19 mg Ca ion Copyright Cengage Learning. All rights reserved 69 Copyright Cengage Learning. All rights reserved 70 Section Acid-Base Titrations A neutralization reaction in which a measured volume of an acid or a base of known concentration is completely reacted with a measured volume of a base or an acid of unknown concentration. For a strong acid and base reaction: H + (aq) + OH (aq) H 2 O(l) Section Acid-Base Titrations Titration Setup Copyright Cengage Learning. All rights reserved 71 Copyright Cengage Learning. All rights reserved 72 12

13 Section Acid-Base Titrations Acid-Base Indicator A compound that exhibits different colors depending on the ph of its solution. An indicator is selected that changes color at a ph that corresponds as nearly as possible to the ph of the solution when the titration is complete. Section Acid-Base Titrations Indicator yellow in acidic solution; red in basic solution Copyright Cengage Learning. All rights reserved 73 Copyright Cengage Learning. All rights reserved 74 Section Acid-Base Titrations Concept Check Section Acid-Base Titrations Concept Check For the titration of sulfuric acid (H 2 SO 4 ) with sodium hydroxide (NaOH), how many moles of sodium hydroxide would be required to react with 1.00 L of M sulfuric acid to reach the endpoint? For the titration of sulfuric acid (H 2 SO 4 ) with sodium hydroxide (NaOH), how many moles of sodium hydroxide would be required to react with 1.00 L of M sulfuric acid to reach the endpoint? H 2 SO 4 + 2NaOH Na 2 SO H 2 O 1.00 mol NaOH Copyright Cengage Learning. All rights reserved 75 Copyright Cengage Learning. All rights reserved 76 13