Chapter 17

Principles of Reactivity:

Chemistry of Acids and Bases

Lecture Notes

 

 

Module 11 Exam Outline

 

 

 

 

Module Eleven: Acid/Base Equilibria Chapter 17

Possible

Actual

 

A. Idenification of Bronsted-Lowry acids&bases

10

 

 

B. Writing Equilibrium Constant Expressions

10

 

 

C. Key Terms Chapter 17

10

 

 

D. Determination of pH & pOH from concentrations Problems

10

 

 

E. Determination of pH of weak acids/bases Problems

10

 

 

F. Hydrolysis Reactions 

10

 

 

G. Common Ion Effect Problem

10

 

 

H. Discussion Questions Chapter 17

5

 

 

I. Determination of pH of polyprotic acids and/or Buffer Calculation Problem

10

 

 

J. Acid-Base Properties of Salts

10

 

 

K. Determination of Kw from Kc ; Kb from Ka & Kw ; Show Kb x Ka = Kw

10

 

 

M. Multiple Choice Applications -Chapter 17

10

 

 

 

 


Chapter 17: Principles of Reactivity: Chemistry of Acids and Bases

 

17.1 Acids, Bases, and the Equilibrium Concept, p. 693

 

Properties of Acids Properties of Bases

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Acid

Base

Arrhenius or Classical definition

 

 

Bronsted - Lowry definition

 

 

Lewis

 

 

 

Acids and bases can be weak or strong electrolytes depending on how much they ionize.

 

Strong electrolytes ionize ___________________.

Weak Electrolytes ionize ___________________.

 

(CD-Rom, Screen 7.5)

Animation Ionization of Nitric Acid:: http://www.lsua.info/chem1212/movies/17ionHNO3.MOV

 

Consider the strong acid, HCl, hydrochloric acid.

Provide its ionization reaction: (Reaction with water.)

 

 

 

 

 

Consider the weak acid, CH3CO2H, acetic acid.

Provide its ionization reaction:

Provide its equilibrium expression: (K is sometimes referred to as the ionization constant, not just the equilibrium constant.)

 

 

 

 

 

Acids and bases that ionize extensively, with K>1, are referred to as:

strong acids or bases.

Acids and bases that do not ionize extensively, with K<1, are referred to as:

weak acids or bases.

 

 

17.3 Bronsted Concept of Acids and Bases

(CD-Rom, Screen 7.2)

ACIDS

 

Name

Formula

Mono, di, or triprotic

Weak/Strong

Hydrochloric acid

HCl

 

 

Hydrobromic acid

HBr

 

 

Hydroiodic acid

HI

 

 

Sulfuric acid

H2SO4

 

 

Nitric acid

HNO3

 

 

Perchloric acid

HClO4

 

 

Carbonic acid

H2CO3

 

 

Hydrofluoric acid

HF

 

 

Phosphoric acid

H3PO4

 

 

Phosphorus acid

H3PO3

 

 

Sulfurous acid

H2SO3

 

 

Hydrosulfuric acid

H2S

 

 

Hydrocyanic acid

HCN

 

 

Acetic acid

CH3CO2H

 

 

 

Monoprotic Acid - ______________________________________________________

Diprotic Acid- _________________________________________________________

Triprotic Acid - ________________________________________________________

Polyprotic Acid - ______________________________________________________

 

Ionization Reactions for H3PO4

 

______________________________________________________________________

 

______________________________________________________________________

 

______________________________________________________________________

 

 

BASES

 

Name

Formula

Mono, di, or triprotic

Weak/Strong

Hydroxide ion

OH-1

 

 

Ethoxide ion

CH3CH2O-1

 

 

Amide ion

NH2-1

 

 

Hydride ion

H-1

 

 

Sulfide ion

S-2

 

 

Carbonate ion

CO3-2

 

 

Bicarbonate ion

HCO3-1

 

 

Sulfate ion

SO4-2

 

 

Phosphate ion

PO4-3

 

 

Hydrogen Sulfide ion

HS-1

 

 

Cyanide ion

CN-1

 

 

Acetate ion

CH3CO2-1

 

 

Ammonia

NH3

 

 

 

Monoprotic Base - ______________________________________________________

Diprotic Base- _________________________________________________________

Triprotic Base - ________________________________________________________

Polyprotic Base - ______________________________________________________

 

Ionization Reaction for NH3

 

_____________________________________________________________________

Animation: Ionization of NH3:

http://www.lsua.info/chem1212/movies/17ionNH3.MOV

Ionization Reactions for CO3-2

 

______________________________________________________________________

 

______________________________________________________________________

 

Amphiprotic - __________________________________________________________

Amphoteric - __________________________________________________________

 

Examples:

 

(Prove by showing ionization reactions.)

 

 

 

 

 

 

 

 

Conjugate Acid - _________________________

Conjugate Base - _________________________

 

Identify the acid, base, conjugate acid, and conjugate base in the following reactions.

 

HBr + NH3 NH4+1 + Br-1

 

 

 

 

HSO3-1 + H2PO4-1 HPO4-2 + H2SO3

 

 

 

 

 

Sample Test: Part A. Idenification of Bronsted-Lowry acids&bases

 

17.3     Water and the pH Scale, p. 697

(CD-Rom, Screen 7.3)

 

Animation of Water Autoionization:

http://www.lsua.info/chem1212/movies/17ionH2O.MOV

 

Water Autoionization and the Water Ionization Constant, Kw

 

2 H2O(l) H3O+(aq) + OH-(aq)

Kw = =

 

 

where Kw is the __________ ____ for water.

 

What happened to the concentration of the water in the above expression?

 

Under neutral conditions, at 25 oC.

[H3O+] =________________

[OH-] = _________________

 

Under acidic conditions, at 25 oC.

[H3O+] =________________

[OH-] = _________________

 

 

Under basic conditions, at 25 oC.

[H3O+] =________________

[OH-] = _________________

 

Are the following solutions, acidic or basic?

 

1.      [H3O+] = 3.2 x 10-11

2.      [OH-] = 2.1 x 10-9

3.      [OH-] = 8.1 x 10-3

 

Exercise 17.3, p. 699

A solution of the strong acid HCl has [HCl] = 4.0 x 10-3 M. What are the concentrations of H3O+ and OH- in this solution?

 

 

 

 

 

pH Scale

(CD-Rom, Screen 7.4)

 

pH scale is another way to express _____________. It avoids using small numbers and exponential notation.

 

pH Scale

 

Acidic

Neutral

Basic

pH

 

 

 

[H3O+]

 

 

 

 

pOH Scale

 

Basic

Neutral

Acidic

pOH

 

 

 

[OH-]

 

 

 

 

Equations:

pH = -log [H3O+]

pOH = -log [OH-]

pH + pOH = 14

Kw = [H3O+] [OH-] = 1 x 10-14

 

 

Two ways to determine pH

1)      _______________________

2) _______________________ (see p. 700, Figure 17.2)

 

 

Exercise 17.4, p. 701

a)      What is the pH of a 0.0012 M NaOH solution?

 

 

 

 

 

 

 

 

 

 

b)      The pH of a diet soda is 4.32 at 25 oC. What are the hydronium and hydroxide ion concentrations in the soda?

 

 

 

 

 

 

 

c)      If the pH of a solution of the strong base Sr(OH)2 is 10.46, what is the concentration of Sr(OH)2 in mol/L?

 

 

 

 

 

 

 

17.4       Equilibrium Constants for Acids and Bases, p. 701

(CD-Rom, Screen 7.6)

 

Strong Acids and Bases

 

For a strong acid, [H3O+] in solution is equal to the original acid concentration. Similarly, for a strong base, [OH-] equals the original base concentration.

 

 

Weak Acids and Bases

 

What is the molarity of water at 25oC?

 

 

 

The strength of weak acids and bases is based on their ability to ___________________.

______________________are used to access their ability to _____________________.

 

Write for the following reaction:

 

K =

____________________________

 

HA(aq) + H2O(l) H3O+(aq) + A-(aq)

 

What effect on the concentration of water does the reaction above occur, if the amount that ionizes is very small compared to the original concentration of HA?

 

 

What is the difference between K and Ka expressions?

 

 

Write the Ka for the above reaction:

 

Ka = ___________________

 

 

where Ka is the _____________ constant or _____________ constant for an _________.

 

B(aq) + H2O(l) BH+(aq) + OH-(aq)

 

 

Kb = ___________________

 

 

where Kb is the _____________ constant or _____________ constant for a _________.

 

The larger the Ka or Kb value the more the acid or base_____________ and the ________________ the acid or base.

 

Sample Exam: Part B. Writing Equilibrium Constant Expressions

 

See page 702, Table 17.3

List of acids and bases and their corresponding Ka and Kb values.

 

 

Note from the chart,

The stronger the acid, the _______________ the conjugate base.

The weaker the acid, the _______________ the conjugate base.

(Trend is also true for bases and their conjugate acids.)

 

Exercise 17.5, p. 705

Use Table 17.3 to answer the following questions.

a)      Which is the stronger acid, H2SO4 and H2SO3?

 

b)      Is benzoic acid, C6H5CO2H, stronger or weaker than acetic acid?

 

c)      Which has the stronger conjugate base, acetic acid or boric acid?

 

d)      Which is the stronger base, ammonia or the acetate ion?

 

e)      Which has the stronger conjugate acid, ammonia or the acetate ion?

 

 

Acid-Base Properties of Salts

(CD-Rom, Screen 7.11)

 

Salt - ionic compound formed from the reaction of an ________________________.

 

Examples:

 

 

 

________________occurs when a salt dissolves in water and causes changes in H3O+ and OH- concentrations.

 

(Many of the bases we already mentioned are found in the form of salts.)

 

Table 17.5 Acid-Base Properties of Ions in Aqueous Solution

 

Neutral

Basic

Acidic

Anions

Cl-1, Br-1, I-1, NO3-1, ClO4-1

CH3CO2-1, HCO3-1,

CO3-2, S-2, F-1, CN-1, PO4-3, HS-1, NO2-1, SO4-2, HPO4-2, SO3-2, Cl0-1

HSO4-1, H2PO4-1, HSO3-1

Cations

Li+1, Na+1, K+1, Mg+2, Ca+2, Ba+2

Al(H2O)5(OH)2+ and analogous ions

Al+3 or Al(H2O)63+ NH4+1, Transition Metal Ions hydrated or not.

 

The acid-base strength of the salt depends on the combination of acidic and basic ions.

Exercise 17.15, page 830

For each salt below, predict whether the pH will be greater than, less than, or equal to 7.

a)      KBr

b)      NH4NO3

c)      AlCl3

d)      Na2HPO4

 

Sample Exam: Part J J. Acid-Base Properties of Salts

A logarithmic Scale of Relative Acid Strength, pKa

 

pKa is used in many cases to compare acid strength (used almost exclusively in organic).

 

pKa = - log Ka

 

See examples on p. 707.

The pKa becomes smaller as the acid strength ________________.

 

Exercise 17.7, p. 707

a)      What is the pKa value for benzoic acid, C6H5CO2H? (Ka = 6.3 x 10 -5 )

 

 

 

 

b)      Is chloroacetic acid (ClCH2CO2H), pKa = 2.87, a stronger or weaker acid than benzoic acid?

 

c)      What is the pKa for the conjugate acid of ammonia? Is this acid stronger or weaker than acetic acid? (From text, pKa of acetic acid is 4.74.)

 

 

 

 

 

Relating the Ionization Constants for an Acid and Its Conjugate Base

 

The connection:

Ka x Kb = Kw

 

Using the ionization reaction of HCN in water, demonstrate the development of the above formula from the Ka of HCN and its conjugate base Kb of CN-

 

 

 

 

Exercise 17.8, page 813

Ka for lactic acid, CH3CHOHCO2H, is 1.4 x 10-4. What is the Kb for the conjugate base of this acid, CH3CHOHCO2-1? (Write a shortened version of the ionization reactions for both.)

 

 

 

 

 

 

 

17.5 Equilibrium Constants and Acid-Base Equilibria, p. 708

 

Predicting the Direction of Acid-Base Reactions using Equilibrium Constants

 

Equilibrium always lies to the side of the weaker acid.

Consider the ionizations of HCl and CH3CO2H. Add the double arrows. Where does the equilibrium lie?

 

HCl + H2O

 

 

CH3CO2H + H2O

 

 

(Use Table 17.3 on page 702, to make decisions.)

 

Exercise 17.9, page 710

a)      Which is the stronger Bronsted acid, HCO3-1 or NH4+1? Which has the stronger conjugate base?

 

 

 

 

b)      Is a reaction between HCO3- ions and NH3, product- or reactant-favored?

HCO3-1 + NH3 NH4+1 + CO3-2

 

 

 

 

Exercise 17.10, page 710

Write the net ionic equation for the possible reaction between acetic acid and sodium hydrogen sulfate, NaHSO4. Does the equilibrium lie to the left or right?

 

 

 

17.6       Types of Acid-Base Reactions, p. 710

(CD-Rom, Screen 7.7)

 

Acid - Base Reactions

 

Combination

Type of Solution formed Assuming Equal Molar Concentrations are Mixed

Strong Acid + Strong Base

 

Strong Acid + Weak Base

 

Strong Base + Weak Acid

 

Weak Acid + Weak Base

 

 

See Table 17.5, p. 711

 

Examples:

Strong Acid/Strong Base

 

 

 

 

 

 

 

Strong Acid/Weak Base

 

 

 

 

 

 

Weak Acid/Strong Base

 

 

 

 

 

Weak Acid/Weak Base

 

 

 

 

 

 

 

 

Exercise 17.11, p. 712

(Assess products when making a decision.)

a)      Equal molar quantities of HCl(aq) and NaCN(aq) are mixed. Is the resulting solution acidic, basic, or neutral?

 

 

 

 

 

b)      Equal molar quantities of acetic acid and sodium sulfite, Na2SO3 are mixed is the resulting solution acidic, basic, or neutral?

 

 

 

17.7 Calculations with Equilibrium Constants, p. 713

 

Calculating Ka from pH

 

Exercise 17.12, page 713

A solution prepared from 0.055 mol of butanoic acid dissolved in sufficient water to give 1.0 L of solution has a pH of 2.72. Determine Ka for butanoic acid. The acid ionizes at according to the balanced equation.

CH3CH2 CH2CO2H(aq) + H2O H3O+1 + CH3CH2 CH2CO2-1(aq)

 

 

CH3CH2 CH2CO2H

H3O+1

CH3CH2 CH2CO2-1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

To sometimes avoid a quadratic equation:

the approximation method may be applied when

[HA] > 100 Ka or [B] > 100 Kb

 

In these cases ionization of the acid or base will be less than 10%.

In the approximation method, X is assumed to be very small. Any X's that are being added or subtracted in the equilibrium constant expression are dropped from the equation.

 

Exercise 17.13, page 716

What are the equilibrium concentrations of acetic acid, the acetate ion, and hydronium ion for a 0.10 M solution of acetic acid (Ka = 1.8 x 10-5)? What is the pH of the solution?

 

Ionization Reaction:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Equation for % Ionization

% ionization = (quantity of acid ionized / initial acid concentration) x 100

 

Calculate the % ionization for the previous problem.

 

 

 

 

 

 

 

Exercise 17.14, page 716

[HF] = 0.015 M, Ka of HF = 7.2 x 10-4

Could the approximation short cut be used in this problem to find equilibrium concentrations?

 

 

 

 

 

 

 

 

 

What is the pH of a 0.025 M solution of ammonia, NH3? (Kb of NH3 is 1.8 x 10-5)

 

Ionization Reaction:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

What is the pH of the Solution after an Acid-Base Reaction?

 

Example 17.8, p. 717

What is the pH of the solution that results from mixing 25 mL of 0.016 M NH3 and 25 mL of 0.016 M HCl?

 

 

 

 

 

 

 

 

 

 

 

Exercise 17.16, p. 718

Calculate the pH after mixing 15 mL of 0.12 M acetic acid with 15 mL of 0.12 M NaOH. What are the major species in solution at equilibrium (besides water) and what are their concentrations?

 


17.8 Polyprotic Acids and Bases, p. 719

 

In ionizations of polyprotic acids and bases, assume that the majority of the hydronium or hydroxide concentration is released in the _________________ionization and that this concentration is used throughout all calculations.

 

Exercise 17.17, page 720

What is the pH of a 0.10 M solution of oxalic acid, H2C2O4? What are the concentration of H3O+, HC2O4-, and the oxalate ion, C2O4-2 ?

 

Provide the two ionization reactions.

 

____________________________________________________ Ka1 = 5.9 x 10-2

 

____________________________________________________ Ka2 = 6.4 x 10-5

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

17.9 Lewis Concept of Acids and Bases,

p. 720 (CD-Rom, Screen 17.12, 13, and 14)

 

Lewis Acid - __________________________

Lewis Base - __________________________

 

Lewis Acid Base Reaction

 

 

 

 

 

 

 

 

Example of Transition Metal Complexes

(See Figure 17.7, page 722)

[Cu(NH3)4]+2

 

 

 

 

 

 

Exercise 17.10, p. 724

Describe each of the following as a Lewis Acid or a Lewis Base

a)      PH3

b)      BCl3

c)      H2S

d)      HS-1

17.10 Molecular Structure, Bonding, and Acid-Base Behavior, p. 724

 

Increasing acid strength ---

HF HCl HBr HI

PKa +3.14 -7 -9 -10

 

Bond Strength 565 432 366 299

in kJ/mol Decreasing Bond Strength ---

 

 

 

 

HNO2 HNO3

 

----------Increasing Acid Strength-----

 

HClO HClO2 HClO3 HClO4

 

 

 

 

Why?

Inductive Effect - the more _____________ there are in the molecule, the more these _______________ atoms pull the electron density back into the molecule, allowing _______ to be released more easily.

 

Why is a H+ removed from acetic acid at -OH and not the -CH?

 

 

 

 

 

 

 

 

 

Exercise 17.19, p. 729

a)      Which is the stronger acid, H2TeO3 or H2TeO4?

 

b)      Which is the stronger acid Fe(H2O)62+ or Fe(H2O)63+?

 

c)      Which is the stronger acid, HOCl or HOBr?

 

d)      The molecule whose structure is illustrated here is amphetamine, a stimulant. Is the compound a Bronsted Acid, a Lewis base, a Bronsted Base, or some combination of these?