Chapter 17
Principles of
Reactivity:
Chemistry of
Acids and Bases
Lecture Notes
Module 11 Exam
Outline
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Module Eleven:
Acid/Base Equilibria Chapter 17 |
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I. Determination
of pH of polyprotic acids and/or Buffer Calculation Problem |
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K. Determination of Kw from Kc ;
Kb from Ka & Kw ; Show Kb x Ka = Kw |
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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
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Acid |
Base |
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Arrhenius
or Classical definition |
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Bronsted
- Lowry definition |
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Lewis |
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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
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Name |
Formula |
Mono, di, or triprotic |
Weak/Strong |
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Hydrochloric
acid |
HCl |
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Hydrobromic
acid |
HBr |
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Hydroiodic
acid |
HI |
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Sulfuric
acid |
H2SO4 |
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Nitric
acid |
HNO3 |
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Perchloric
acid |
HClO4 |
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Carbonic
acid |
H2CO3 |
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Hydrofluoric
acid |
HF |
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Phosphoric
acid |
H3PO4 |
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Phosphorus
acid |
H3PO3 |
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Sulfurous
acid |
H2SO3 |
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Hydrosulfuric
acid |
H2S |
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Hydrocyanic
acid |
HCN |
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Acetic
acid |
CH3CO2H |
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Monoprotic
Acid - ______________________________________________________
Diprotic
Acid- _________________________________________________________
Triprotic
Acid - ________________________________________________________
Polyprotic
Acid - ______________________________________________________
Ionization
Reactions for H3PO4
______________________________________________________________________
______________________________________________________________________
______________________________________________________________________
BASES
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Name |
Formula |
Mono, di, or triprotic |
Weak/Strong |
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Hydroxide
ion |
OH-1 |
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Ethoxide
ion |
CH3CH2O-1 |
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Amide ion |
NH2-1 |
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Hydride
ion |
H-1 |
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Sulfide
ion |
S-2 |
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Carbonate
ion |
CO3-2 |
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Bicarbonate
ion |
HCO3-1 |
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Sulfate
ion |
SO4-2 |
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Phosphate
ion |
PO4-3 |
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Hydrogen
Sulfide ion |
HS-1 |
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Cyanide
ion |
CN-1 |
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Acetate
ion |
CH3CO2-1 |
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Ammonia |
NH3 |
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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 ó NH4+1 +
Br-1
HSO3-1 +
H2PO4-1 ó 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) ó H3O+(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+]
=________________
[
Under
acidic conditions, at 25 oC.
[H3O+]
=________________
[
Under
basic conditions, at 25 oC.
[H3O+]
=________________
[
Are
the following solutions, acidic or basic?
1. [H3O+]
= 3.2 x 10-11
2. [
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
pH Scale
(CD-Rom,
Screen 7.4)
pH
scale is
another way to express _____________. It
avoids using small numbers and exponential notation.
pH Scale
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Acidic |
Neutral |
Basic |
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pH |
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[H3O+] |
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pOH Scale
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Basic |
Neutral |
Acidic |
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pOH |
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Equations:
pH
= -log [H3O+]
pOH
= -log [
pH +
pOH = 14
Kw
= [H3O+] [
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) ó 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) ó BH+(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
(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
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Neutral |
Basic |
Acidic |
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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 |
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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 ó 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
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Combination |
Type of Solution formed
Assuming Equal Molar Concentrations are Mixed |
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Strong Acid +
Strong Base |
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Strong Acid +
Weak Base |
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Strong Base +
Weak Acid |
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Weak Acid +
Weak Base |
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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 ó H3O+1 +
CH3CH2 CH2CO2-1(aq)
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CH3CH2
CH2CO2H |
H3O+1 |
CH3CH2
CH2CO2-1 |
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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:
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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:
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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
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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
---à
HF HCl HBr HI
PKa +3.14 -7 -9 -10
Bond
Strength 565 432 366 299
in
kJ/mol Decreasing Bond Strength
---à
HNO2 HNO3
----------Increasing
Acid Strength-----à
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?
