acids and bases...acids and bases brønstedacids and bases (16.1) the acid-base properties of water...

Acids and Bases

Acids and Bases Brønsted Acids and Bases (16.1) The Acid-Base Properties of Water (16.2) pH – A Measure of Acidity (16.3) Strength of Acids and Bases (16.4) Weak Acids and Acid Ionization Constants (16.5) Weak Bases and Base Ionization Constants (16.6) The Relationship Between Conjugate Acid-Base

Ionization Constants (16.7) Molecular Structure and the Strength of Acids

(16.8) Acid-Base Properties of Salts (16.9) Acidic, Basic, and Amphoteric Oxides (16.10) Lewis Acids and Bases (16.11)

General Chemistry I – Concepts Representations of matter (1.3-1.4) Formula calculations and stoichiometry (3.6-

3.9) Strong and weak acids and bases, molar

concentrations of solutions and solution stoichiometry (4.4-4.6)

Periodicity of the elements and descriptive chemistry (8.6)

Lewis dot structures and electronegativities(9.4 and 9.5)

Molecular shape and polarity (10.1 and 10.2)

16.1 Brønsted Acids and Bases

What is an acid?◦ Review: Arrhenius acids◦ Review: Brønsted acids

Review: Which definition is more encompassing?

Review: What are weak versus strong acids and bases?

What is a base?◦ Review: Arrhenius bases◦ Review: Brønsted bases

Review: Which definition is more encompassing?

Review: What are weak versus strong acids and bases?

What is a conjugate acid/base pair?

Review: What is a better way to describe the

hydrogen ion in water? H+ or H3O+

16.1 Brønsted Acids and Bases Describe the reaction in water of HF

forming H+ versus H3O+.

2HF aq H O l

What is a conjugate acid/base pair?

Practice: What is the conjugate acid of ammonia? What is the conjugate base of acetic acid?

16.2 The Acid-Base Properties of Water

What is the conjugate acid of water? What is the conjugate base of water? What the definition of amphoteric? How is this equilibrium represented

symbolically?

2 2 3H O l H O l H O aq OH aq

2H O l H aq OH aq

Explain how water is amphoteric.

How is this equilibrium represented in an equilibrium expression?

What is the value of the equilibrium constant (at 25oC)?

What does this tell us about the concentration of the:◦ Hydrogen ion◦ Hydroxide ion

16.2 The Acid-Base Properties of Water Ion-product constant (of water), Kw:◦ The product of the molar concentrations of H+ and

OH- ions at a particular temperature What is the equilibrium expression and what is

true when the solution is neutral? What does this tell us about the concentration of

the:◦ Hydrogen ion In acidic solution In basic solution

◦ Hydroxide ion In acidic solution In basic solution

Ion-product constant (of water), Kw

Solution [H+] [OH-]Acidic, basic or neutral

1 10-7 M2 10-5 M3 10-9 M

2H O l H aq OH aq

o 1425 1.0 10wK C H OH

1 10-7 M 10-7 M neutral2 10-5 M3 10-9 M

2H O l H aq OH aq

o 1425 1.0 10wK C H OH

1 10-7 M 10-7 M neutral2 10-5 M 10-9 M acidic3 10-9 M

2H O l H aq OH aq

o 1425 1.0 10wK C H OH

1 10-7 M 10-7 M neutral2 10-5 M 10-9 M acidic3 10-9 M 10-5 M basic

2H O l H aq OH aq

o 1425 1.0 10wK C H OH

What is present in an acidic solution? What is present in a basic solution?

1 10-7 M 10-7 M neutral2 10-5 M 10-9 M acidic3 10-9 M 10-5 M basic

Acidic solution

Solution [HCl] [H+] [OH-] Strength?1 0.01 M2 0.001 M3 0.0001 M

2 3HCl aq H O l H O aq Cl aq

HCl aq H aq Cl aq

2 , 251.0 10

w CH O l H aq OH aq K

HCl aq H aq Cl aq

Concentration of HCl and H+ in solutionC

0.01 M HCl (aq)In solution: 0.01 M H+

and 0.01 M Cl-

H+ / Cl-

Acidic solution

Solution [HCl]0 [H+] [OH-] Strength?1 0.01 M 0.01 M2 0.001 M3 0.0001 M

HCl aq H aq Cl aq

2 , 251.0 10

Acidic solution

Solution [HCl]0 [H+] [OH-] Strength?1 0.01 M 0.01 M2 0.001 M 0.001 M3 0.0001 M 0.0001 M

HCl aq H aq Cl aq

2 , 251.0 10

Acidic solution

Solution [HCl]0 [H+] [OH-] Strength?1 0.01 M 0.01 M 10-12 M strongest2 0.001 M 0.001 M 10-11 M3 0.0001 M 0.0001 M 10-10 M weakest

HCl aq H aq Cl aq

2 , 251.0 10

Basic solution

Solution [NaOH]0 [OH-] [H+] Strength?1 0.01 M2 0.001 M3 0.0001 M

NaOH aq Na aq OH aq

2 , 251.0 10

NaOH aq Na aq OH aq

Concentration of NaOH and OH- in solutionC

0.01 M NaOH (aq)In solution: 0.01 M Na+

and 0.01 M OH-

Na+ / OH-

Basic solution

Solution [NaOH]0 [OH-] [H+] Strength?1 0.01 M 0.01 M2 0.001 M 0.001 M3 0.0001 M 0.0001 M

NaOH aq Na aq OH aq

2 , 251.0 10

Basic solution

Solution [NaOH]0 [OH-] [H+] Strength?1 0.01 M 0.01 M 10-12 M strongest2 0.001 M 0.001 M 10-11 M3 0.0001 M 0.0001 M 10-10 M weakest

NaOH aq Na aq OH aq

2 , 251.0 10

What is the trend of ◦ acid strength (acidity) and the concentration

of the hydrogen ion?◦ basic strength (basicity) and the concentration

of the hydroxide ion?◦ basic strength (basicity) and the concentration

of the hydrogen ion?

16.3 pH – A Measure of Acidity

Acid strength and [H+]

Acidity

Acid strength decreasing

Acidity

Acid strength and [OH-]

Basic strength and [OH-]

Basicity

Basic strength decreasing

Basicity

Basic strength and [H+]

Basic strength decreasing

Acid strength and [H+]

Acidity

What if we plotted this on a log scale instead? First consider the data for an acidic solution[H+] log [H+] -log[H+] [OH-] Acidity

0.01 M0.001 M0.0001 M

10-5 M10-6 M

10-7 M

0.01 M Strong0.001 M0.0001 M

10-5 M10-6 M Weak

10-7 M neutral

0.01 M 10-12 M Strong0.001 M 10-11 M0.0001 M 10-10 M

10-5 M 10-9 M10-6 M 10-8 M Weak

10-7 M 10-7 M neutral

0.01 M -2 10-12 M Strong0.001 M -3 10-11 M0.0001 M -4 10-10 M

10-5 M -5 10-9 M10-6 M -6 10-8 M Weak

10-7 M -7 10-7 M neutral

0.01 M -2 2 10-12 M Strong0.001 M -3 3 10-11 M0.0001 M -4 4 10-10 M

10-5 M -5 5 10-9 M10-6 M -6 6 10-8 M Weak

10-7 M -7 7 10-7 M neutral

What if we plotted this on a log scale instead?

Acidity

What if we plotted this on a log scale instead? First consider the data for a basic solution

[OH-] [H+] log[H+] -log[H+] Basicity0.01 M0.001 M0.0001 M

10-5 M10-6 M

10-7 M

[OH-] [H+] log[H+] -log[H+] Basicity0.01 M Strong0.001 M0.0001 M

10-5 M10-6 M Weak

10-7 M neutral

[OH-] [H+] log[H+] -log[H+] Basicity0.01 M 10-12 M Strong0.001 M 10-11 M0.0001 M 10-10 M

10-5 M 10-9 M10-6 M 10-8 M Weak

10-7 M 10-7 M neutral

[OH-] [H+] log[H+] -log[H+] Basicity0.01 M 10-12 M -12 Strong0.001 M 10-11 M -110.0001 M 10-10 M -10

10-5 M 10-9 M -910-6 M 10-8 M -8 Weak

10-7 M 10-7 M -7 neutral

[OH-] [H+] log[H+] -log[H+] Basicity0.01 M 10-12 M -12 12 Strong0.001 M 10-11 M -11 110.0001 M 10-10 M -10 10

10-5 M 10-9 M -9 910-6 M 10-8 M -8 8 Weak

10-7 M 10-7 M -7 7 neutral

What if we plotted this on a log scale instead?

Basicity

Base strength increasing

What is pH◦ algorithmically?◦ as a measure of acid strength?

[H+] log [H+] -log[H+] [OH-] Acidity0.01 M -2 2 10-12 M Strong0.001 M -3 3 10-11 M0.0001 M -4 4 10-10 M

10-5 M -5 5 10-9 M10-6 M -6 6 10-8 M Weak

10-7 M -7 7 10-7 M neutral

pH and acid strength

Acidity

What is pH◦ algorithmically?◦ as a measure of acid strength?

Type of solution

[H+] vs. [OH-] [H+] [OH-] pH

Acidic [H+] > [OH-] [H+] >10-7 M [OH-] <10-7 M pH < 7NeutralBasic

What is pOH◦ algorithmically?◦ as a measure of acid strength?

[H+] pH [OH-] pOH Acidity0.01 M 2 10-12 M Strong0.001 M 3 10-11 M0.0001 M 4 10-10 M

10-5 M 5 10-9 M10-6 M 6 10-8 M Weak

10-7 M 7 10-7 M neutral

[H+] pH [OH-] pOH Acidity0.01 M 2 10-12 M 12 Strong0.001 M 3 10-11 M 110.0001 M 4 10-10 M 10

10-5 M 5 10-9 M 910-6 M 6 10-8 M 8 Weak

10-7 M 7 10-7 M 7 neutral

How are pH and pOH related?

Type of solution

[H+] vs. [OH-] [OH-] pH pOH

AcidicNeutral [H+] = [OH-] [OH-] =10-7 M pH = 7 pOH = 7Basic

Practice:

What is the [H+] and pH of◦ 0.0015 M HNO3

◦ 0.0015 M Ba(OH)2

16.4 Strength of Acids and Bases

Review: What is a strong acid?

Review: What species are present for HCl?

Review: What is a weak acid?

Review: What species are present for HF?

Figure 16.3 p. 555

HCl aq H aq Cl aq

Concentration of HCl and H+ in solutionC

0.01 M HCl (aq)In solution: 0.01 M H+

and 0.01 M Cl-

H+ / Cl-

HF aq H aq F aq

Concentration of HF and H+ in solutionC

0.01 M HF (aq)In solution: 0.00734 M HF

and 0.00266 M H+

Review: What is a strong acid? Review: What is a weak acid? What is the conjugate base of the strong

acid, HCl?◦ What is the relative strength of the conjugate

base of HCl? What is the conjugate base of the weak

acid, HF?◦ What is the relative strength of the conjugate

base of HF?

What is the general trend of relative strength of acid/base pairs?◦ Strong acids and their conjugate bases◦ Weak acids and their conjugate bases

Table 16.2 p. 556

What is the strongest acid that can exist in aqueous solution?

What is the strongest base that can exist in aqueous solution?

What does this mean for Table 16.2?

Table 16.2 p. 556

What is present in a solution of◦ HCl◦ HF◦ NaOH◦ NH3

What is the general trend of relative strength of acid/base pairs in terms of:◦ hydrogen ion concentration?◦ pH?

16.5 Weak Acids and Acid Ionization Constants Review: What is the equilibrium

expression for the ionization of HF?

Review: What is the equilibrium expression for the ionization of any weak acid?

How does this equilibrium constant, Ka, tell us about acid strength?

Table 16.3 p. 559

16.5 Weak Acids and Acid Ionization Constants How does this equilibrium constant, Ka,

tell us about acid strength? Which solution will have a higher [H+]?◦ HF Ka = 7.1x10-4

◦ HNO2 Ka = 4.5x10-4

tell us about acid strength? Which solution will have a lower pH?◦ HF Ka = 7.1x10-4

◦ HNO2 Ka = 4.5x10-4

tell us about acid strength? What is the pH of 0.015 M:◦ HF Ka = 7.1x10-4

◦ HNO2 Ka = 4.5x10-4

When can you approximate and what is the 5% rule?

16.5 Weak Acids and Acid Ionization Constants How does this equilibrium constant, Ka, tell

us about acid strength? Percent ionization:◦ The ratio of ionized acid concentration at

equilibrium over the initial concentration of the acid

How does this tell us about acid strength? Which solution would have a greater

percent ionization?◦ 0.015 M HF Ka = 7.1x10-4

◦ 0.015 M HNO2 Ka = 4.5x10-4

How does percent ionization tell us about acid strength?

16.5 Weak Acids and Acid Ionization ConstantsHow do [H+], pH and percent ionization vary for the same acid but decreasing concentrations?

HF [H+] pH Percent ionization0.01 M

0.0015 M0.001 M

0.00015 M0.0001 M

0.000015 M

HF [H+] pH Percent ionization0.01 M 0.0081 M

0.0015 M 0.0029 M0.001 M 0.0023 M

0.00015 M 0.00074 M0.0001 M 0.00056 M

0.000015 M 0.00013 M

HF [H+] pH Percent ionization0.01 M 0.0081 M 2.09

0.0015 M 0.0029 M 2.530.001 M 0.0023 M 2.63

0.00015 M 0.00074 M 3.130.0001 M 0.00056 M 3.25

0.000015 M 0.00013 M 3.90

HF [H+] pH Percent ionization0.01 M 0.0081 M 2.09 8.1%

0.0015 M 0.0029 M 2.53 19.5%0.001 M 0.0023 M 2.63 23.3%

0.00015 M 0.00074 M 3.13 49.1%0.0001 M 0.00056 M 3.25 55.9%

0.000015 M 0.00013 M 3.90 84.8%

16.5 Weak Acids and Acid Ionization Constants What happens to percent ionization as

concentration decreases? Why is this only true for weak

acids/bases?

Figure 16.4 p. 565

16.5 Weak Acids and Acid Ionization Constants What about acids with more than one

acidic hydrogen?◦ What species do these acids have in solution?◦ How do we write the equilibrium

expressions?◦ What would you predict about the relative

size of Ka1 versus Ka2 versus Ka3?

Table 16.4 p. 563

16.5 Weak Acids and Acid Ionization Constants Practice:

What is the concentration of all species at equilibrium of a 1.0 M phosphoric acid solution?

What is the order of the highest concentration to lowest concentration of all species in 1.0 L of solution?

16.6 Weak Bases and Base Ionization Constants Review: What is a strong base? Review: What is a weak base? Review: How do we represent this

symbolically? Review: What species are present for

NaOH versus NH3?

16.6 Weak Bases and Base Ionization Constants Review: What is the equilibrium

expression for the ionization of NH3?

Review: What is the equilibrium expression for the ionization of any weak base?

How does this equilibrium constant, Kb, tell us about base strength?

Table 16.5 p. 570

16.6 Weak Bases and Base Ionization Constants How does this equilibrium constant, Kb,

tell us about base strength? Which solution will have a higher [OH-]?◦ NH3 Kb = 1.8x10-5

◦ CH3NH2 Kb = 4.4x10-4

tell us about base strength? Which solution will have a lower pOH?◦ NH3 Kb = 1.8x10-5

◦ CH3NH2 Kb = 4.4x10-4

tell us about base strength? What is the pOH of 0.015 M:◦ NH3 Kb = 1.8x10-5

◦ CH3NH2 Kb = 4.4x10-4

tell us about base strength? What is the pH of 0.015 M:◦ NH3 Kb = 1.8x10-5

◦ CH3NH2 Kb = 4.4x10-4

16.5 Weak Acids and Acid Ionization Constants How does this equilibrium constant, Kb, tell

us about base strength? Percent ionization:◦ The ratio of ionized base concentration at

equilibrium over the initial concentration of the base

How does this tell us about base strength? Which solution would have a greater

percent ionization?◦ 0.015 M NH3 Kb = 1.8x10-5

◦ 0.015 M CH3NH2 Kb = 4.4x10-4

How does percent ionization tell us about base strength?

16.7 The Relationship Between Conjugate Acid-Base Ionization Constants

Review: What is the conjugate base of HF?

What is the equilibrium expression for the reaction of HF in water?

What is the equilibrium expression for the reaction of F- in water?

Review: What are the rules for multiple reactions and the equilibrium constants?

How is Ka related to Kb? What is the value of Kb of the fluoride

ion? What does Ka > Kb mean? What does Ka < Kb mean?

Practice:

What is Kb for the acids listed below?◦ HNO2

◦ HCN

Which acid is the strongest? Which conjugate base is the strongest?

Table 16.3 p. 559

16.8 Molecular Structure and the Strength of Acids Review: What do we learn from a Lewis

dot structure? How does bond enthalpy and

electronegativity contribute to the strength of acid?

What about HCl versus HBr?Table 16.6 p. 573

16.8 Molecular Structure and the Strength of Acids

How can we verify this trend with experimental data?

(Can the solvent for the system be water?)

What does the equilibrium constant and equilibrium concentrations of HCl versus HBr in acetic acid tell us about acid strength?

16.8 Molecular Structure and the Strength of Acids

What are the Lewis dot structures of:◦ HNO2 versus HNO3

◦ HClO versus HClO2

What are the rules for oxoacid strength? Which structure has a higher oxidation

state of N? Review: What is formal charge? How the Lewis dot structures of the

acids above relate oxoacid strengths?

16.9 Acid-Base Properties of Salts

Review: What is the conjugate base of HF?

Review: What is the conjugate acid of NH3?

To work through these salts:◦ Consider first what happens when the salt

dissociates in water◦ Then consider the reaction of each ion with

water (are either a conjugate acid/base of a weak acid/base)◦ Then consider the production of the

hydroxide ion or hydrogen ion

What happens when NaCl is put in water?

What is the pH of this solution?

What happens when NaF is put in water? What is the pH of this solution?

What happens when NH4Cl is put in water?

What happens when AlCl3 is put in water?

What happens when NH4F is put in water?

Table 16.7 p. 580

16.10 Acidic, Basic and Amphoteric Oxides

What are oxides? What is the oxide of sodium? What is the reaction of sodium oxide in

water?◦ What is the pH of this solution?

What is the general rule of metal oxides?

What are oxides? What is the reaction of dinitrogen

pentoxide in water?◦ What is the pH of this solution?

What is the general rule of nonmetal oxides?

What are amphoteric oxides? What group of elements would you

expect to be amphoteric oxides?

Figure 16.8 p. 582

What type of element forms basic oxides? What type of element forms acidic

oxides? What type of element forms amphoteric

oxides?

16.11 Lewis Acids and Bases What is an acid?◦ Review: Arrhenius acids◦ Review: Brønsted acids◦ Lewis acids A substance that can accept a pair of electrons

What is a base?◦ Review: Arrhenius bases◦ Review: Brønsted bases◦ Lewis bases A substance that can donate a pair of electrons

Which definition is the most encompassing?

16.11 Lewis Acids and Bases

How do Lewis dot structure assist in assigning the Lewis acid or Lewis base in a reaction?

Practice: Carbon dioxide reacts with water. What

is the Lewis acid and Lewis base in this reaction?

Can the ammonium ion be a Lewis base?

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