1. Chapter 17 – Chemistry of Acids and Bases
Objectives:
Know the Bronsted-Lowry and Lewis theories of acids and bases.
Apply chemical equilibrium to acids and bases.
Predict reactions between acids and bases.
Relate structure and bonding to acid-base properties.

2. How do we know ions are present in aqueous solutions?
The solutions conduct electricity!
The substances that provide ions in an aqueous solution are called ELECTROLYTES.
HCl, CuCl2, and NaCl are
__________electrolytes.

3. What is a Strong Electrolyte?
They ionize or dissociate completely (or nearly so) into __________.
HCl, CuCl2, and NaCl are strong electrolytes.
HCl (aq) H+(aq) Cl-(aq)

4. What is a Weak Electrolyte?
Acetic acid ionizes only to a small extent, so it is a weak electrolyte.
CH3CO2H(aq)
CH3CO2-(aq) + H+(aq)

5. An acid - - -> H+ (in water)
What is an Acid?
An acid - - -> H+ (in water)
Some strong acids
(completely ionized) are:
HCl hydrochloric
H2SO4 sulfuric
HClO4 perchloric
HNO3 nitric
PROTON
Because a hydrogen atom is one proton and one electron, a hydrogen ion (H+) is simply a proton.
HNO3

6. An acid ---> H+ in water
What is an Acid?
An acid ---> H+ in water
HCl(aq) H+(aq) + Cl-(aq)

7. What is the Hydronium Ion?
HCl(aq) H+(aq) + Cl-(aq)
HCl H 2 O Cl - 3 +
hydronium
ion
Bronsted – Lowry Theory:
An acid donates a proton

8. What is a Weak Acid? CH3CO2H (aq) H+(aq) + CH3CO2- (aq)
WEAK ACIDS (only partially ionized)
= weak electrolytes
CH3CO2H acetic acid
H2CO3 carbonic acid
H3PO4 phosphoric acid
HF hydrofluoric acid

9. Weak Acid K = [CH3CO2-][H3O+] [CH3CO2H] Equilibrium constants =
= 1.8 x 10-5
K > 1 (larger) – _______ Acid
K < 1 (smaller) – ______ Acid

10. Bronsted-Lowry Acids and Bases
Acid – any substance that can _________ a proton to any other substance.
Base – any substance that can _________ a proton from any other substance.

11. Acids – Monoprotic and Polyprotic

12. Amphiprotic – can behave as _____________________.
Polyprotic bases – can accept ____________proton.

13. Label the following as Acid or Base
HCl
CO32-
CN-
H2SO4
NH4+
NH3
CH3CH2COOH
H2PO4-
HCO3-
H2O

14. Water is amphiprotic – self-ionization of water
Write the equation:

15. Conjugate Acid-Base Pairs
A pair of compounds or ions that differ by the presence of one H+ ion is called a _________________________.
Every reaction between a Bronsted acid and Bronsted base involves ___________________and has two _______________________.

16. Conjugate Acid-Base Identify the conjugate acid-base pairs:
1) HCO3- (aq) + H2O (l) H3O+ (aq) + CO32- (aq)
2) HNO3 (aq) + NH3 (aq) NH4+ (aq) + NO3– (aq)

17. Kw
Kw =

18. Kw and pH Neutral: [H3O+] = [OH-] Kw = [H3O+][OH-]
[H3O+] = [OH-] = √1.0 x 10-14
[H3O+] = [OH-] = 1 x 10-7
pH = __________
Neutral = pH = ________

19. Kw and pH Adding acid to pure H2O: Adding base to pure H2O:
Increases the [H3O+] ; some reacts with the [OH-]
[OH-] is ______________
Equilibrium is reached when [H3O+][OH-] = 1 x (25oC)
[H3O+] ____ 1 x 10-7 M; [OH-] _____ 1 x 10-7 M
Adding base to pure H2O:
Increases the [OH-] ; some reacts with the [H3O+]
[H3O+] is _______________
[H3O+] ___1 x 10-7 M; [OH-] ____ 1 x 10-7 M

20. Look at ionization constants to determine strength of acids and bases.pH
Look at ionization constants to determine strength of acids and bases.

21. A solution of HCl has [HCl] = 4. 0 x 10-3 M
A solution of HCl has [HCl] = 4.0 x 10-3 M. What are the concentrations of H3O+ and OH- in this solution at 25oC?

22. What is the pH of a 0. 0075 M solution of HCl
What is the pH of a M solution of HCl? What is the hydroxide ion concentration of the solution?

23. The pH of a solution of Ba(OH)2 is 9. 89 at 25oC
The pH of a solution of Ba(OH)2 is 9.89 at 25oC. What is the hydroxide ion concentration in the solution? How many grams of Ba(OH)2 must have been dissolved?

24. Other pX Scales pKw = _____ = ____ + _____ In general pX = -log X
and so pOH = - log [OH-]
Kw = [H3O+] [OH-] = x at 25 oC
Take the log of both sides
-log (10-14) = - log [H3O+] + (-log [OH-])
pKw = _____ = ____ + _____

25. Ka and Kb Strong acids have _________ ionization constants (Ka) –
Indicating higher ability of donating protons –
And a ________ pH.
Strong bases have _________ ionization constants (Kb) – Indicating higher ability of accepting protons – And a _________ pH.

26. Ka and Kb Ka = Kb = HA(aq) + H2O(l) H3O+(aq) + A-(aq)
B(aq) + H2O(l) BH+(aq) + OH-(aq)
Kb =

27. K and Reactions
ACIDS CONJUGATE BASES
STRONG
weak
Reactions always go from the stronger A-B pair (_______ K) to the weaker A-B pair (_____ K).

28. K and Reactions A strong acid is __________ %dissociated.
Therefore, a STRONG ACID —a good H+ donor—must have a WEAK CONJUGATE BASE—a poor H+ acceptor:
HNO3(aq) + H2O(liq)  H3O+(aq) + NO3-(aq)
STRONG A base acid weak B
Every A-B reaction has two acids and two bases.
Equilibrium always lies toward the _________ pair.
Here K is very __________.

29. K and Reactions H O + NO HNO + H O STRONG ACID WEAK BASE3 O +
+ NO -
HNO 3
+ H 2 O
STRONG
ACID
WEAK
BASE
We know from experiment that HNO3 is a strong acid.
1. It is a stronger acid than H3O+
2. H2O is a stronger base than NO3-
3. K for this reaction is __________.

30. K and Reactions 1. H3O+ is a stronger acid than HOAc
Acetic acid is only 0.42% ionized when [HOAc] = 1.0 M. It is a _____________________.
HOAc H2O H3O OAc-
Because [H3O+] is small, this must mean
1. H3O+ is a stronger acid than HOAc
2. OAc- is a stronger base than H2O
3. K for this reaction is ___________.

31. Ka and Structure
Inductive effect: adjacent atoms ____________ electrons.
O is very electronegative, it will attract e-
Once a proton is donated, a negative charge is left behind.
The charge needs to be stabilized.

32. Ka and pKa pKa = -logKa pKa = -logKa
The _____________________ structures that can stabilize the charge determines the acidity of the substance.
Because: the negative charge left behind can be distributed over more atoms (providing stability).
Exercise: Draw the resonance structures for NO3- and for NO2-.

33. Ka and Structure

34. Exercise: Draw the resonance structures for NO3- and for NO2-.

35. Ka and Structure
The number of resonance structures that can stabilize the charge determines the acidity of the substance.
Exercise: Draw the resonance structures for acetate ion.

36. Ka and Structure Acidity is favored by:
Electronegative atoms attached.
The possibility of resonance structures for the anion.

37. Ka and Structure
Methyl (CH3-) group increases the electronic density on the O-, making the negative charge more unstable and then acetic acid is less acidic than formic acid.
Propanoate ion is the stronger base (it is eager to accept a proton) because the negative charge is not favored.

38. Kb and Structure
Which is the stronger base?

39. Kb and Structure

40. Substituent Effects
The electron cloud in a σ-bond between two unlike atoms is not uniform and is slightly displaced towards the more electronegative of the two atoms. This causes a permanent state of bond polarization, where the more electronegative atom has a slight negative charge(δ-) and the other atom has a slight positive charge(δ+).
If the electronegative atom is then joined to a chain of atoms, usually carbon, the positive charge is relayed to the other atoms in the chain. This is the electron-withdrawing inductive effect, also known as the -I effect.
Some groups, such as the alkyl group are less electron-withdrawing than hydrogen and are therefore considered as electron-releasing. This is electron releasing character is indicated by the +I effect.

41. The inductive effect

42. Summary: Substance Definition Examples Arrhenius acid
Provides _____in water
Strong acids: HCl, HNO3
Weak acids: HF, HCN
Cations of weak bases: NH4+
Anions of some polyprotic acids: HSO4 -
Arrhenius base
Strong bases: NaOH, Ba(OH)2
Bronsted-Lowry acid
Proton ________
Bronsted-Lowry base
Proton _________
Weak bases: NH3
Anions of weak acids: OH -, CN -
Anions of most polyprotic acids: CO32-, H2PO4 -
Lewis acid
Electron Pair _______
Molecules with an incomplete octet: BF3
Small highly charged cations: Cu2+, Fe+3
Molecules with polar bonds: CO2
Lewis base
Electron Pair ________
Molecules with a lone pair of electrons: H2O, NH3, CO
Anions: Cl -, OH -, CN -

43. Identify the acidic protons and the proton accepting atoms in the following:

44. Answer using table 17.3: Which is the stronger acid?
Benzoic acid or acetic acid
Which has the stronger conjugate base?
Acetic acid or benzoic acid
Which is the stronger base?
Ammonia or acetate ion
Which has the stronger conjugate acid?

45. Aqueous Solutions of Salts
Some ions are Bronsted bases:
Some ions are Bronsted acids:
Anions that are conjugate bases of strong acids (Cl-, NO3-) are such weak bases, they ________________ on pH.
Alkali metal and alkaline earth cations have __________pH.
Anions of polyprotic acids can be either _______________.
Transition metal ions M2+ and M3+ can act as ___________.
___________anions are conjugate bases of weak acids (CO32-, F-, CN-) or ions [Al(H2O)6]3+.
CO32- (aq) + H2O(l) HCO3- (aq) + OH- (aq) Kb = 2.1 x 10-4
[Al(H2O)6]3+ (aq) + H2O(l) [Al(H2O)5 (OH)2+ (aq) + H3O+ (aq)
Ka = 7.9 x 10-6

46. Table 17.4 Acid and Base Properties of Ions in Aqueous Solution

47. For each of the following salts in water, predict whether the pH will be acidic, basic, or neutral.
NaNO3
FeCl2
NH4NO3
NH4F

48. Ka and Kb Relationship
Ka x Kb = Kw

49. Reaction between an Acid and a Base
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?
CH3CO2H (aq) + HSO4- (aq) CH3CO2- (aq) + H2SO4 (aq)

50. Types of acid-base Reactions
Strong acid + Strong base (neutralizations)
Weak acid + Strong base
Strong acid + Weak base
Weak acid + Weak base

51. Strong acid + Strong base
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
H3O+(aq) + Cl-(aq) + Na+(aq) + OH-(aq) Na+(aq) + Cl-(aq) + 2 H2O (l)
H3O+(aq) + OH-(aq) H2O (l)
K = 1/Kw = 1 x 1014
Really large! Reaction goes to completion
Na+ and Cl- have no effect on pH
Final solution should be neutral:
Mixing equal molar amounts of a strong acid with a strong base produces a __________ solution (pH = _____ at 25oC).

52. Weak acid + Strong base HCO2H(aq) + NaOH(aq) HCO2Na(aq) + H2O(l)
HCO2H(aq) + OH-(aq) H2O (l) + HCO2- (aq)
OH- is stronger base than HCO2-
Reaction should proceed to the right forming HCO2Na; Na+ is neutral ion and HCO2- is a basic ion (conjugate base of a weak acid).
Solution is basic.
Mixing equal amounts of a strong base with a weak acid produces a ______ whose anion is the conjugate base of the weak acid. The solution is __________, pH depending on the value of _____________________.

53. Strong acid + Weak base HCl + NH3
H3O+ (aq) + NH3 (aq) H2O (l) + NH4+ (aq)
H3O+ is stronger acid than NH4+
Equilibrium lies to the right
NH4Cl; NH4+ is an acidic ion, Cl- will not affect pH
Mixing equal amounts of a strong acid and a weak base produces a ________ whose cation is the conjugate acid of the weak base. The solution is __________, with the pH depending on the value of ______________.

54. Weak acid + Weak base CH3CO2H is stronger acid than NH4+
Acetic acid + ammonia:
CH3CO2H (aq) + NH3 (aq) NH4+ (aq) + CH3CO2- (aq)
CH3CO2H is stronger acid than NH4+
Equilibrium lies to the right (product favored).
Product is NH4CH3CO2
Ka for NH4+= 5.6 x 10-10
Kb for CH3CO2- = 5.6 x 10-10
Ka = Kb ; solution will be neutral
Mixing equal molar amounts of a weak acid and a weak base produces a ________ whose cation is the conjugate acid of the weak base and whose anion is the conjugate base of the weak acid. The solution pH depends on the ________________________________.

55. CH3CH2CH2CO2H (aq) + H2O (l) H3O+ (aq) + CH3CH2CH2CO2- (aq)
Determine Ka for butanoic acid. A solution prepared from mol of butanoic acid dissolved in sufficient water to give 1.0 L of solution has a pH of 2.72 at 25oC.
CH3CH2CH2CO2H (aq) + H2O (l) H3O+ (aq) + CH3CH2CH2CO2- (aq)

56. HF (aq) + H2O (l) H3O+(aq) + F-(aq)
What are the equilibrium concentrations of HF, F- ion, and H3O+ ion in a M solution of HF? What is the pH of the solution?
HF (aq) + H2O (l) H3O+(aq) + F-(aq)

57. What is the pH of the solution that results from mixing 25 mL of 0
What is the pH of the solution that results from mixing 25 mL of M NH3 and 25 mL of M HCl?
1) Write balanced equation
2) Find amount of product (salt that determines the pH)
3) For pH solve an equilibrium problem

58. Polyprotic Acids and Bases
The pH of many inorganic polyprotic acids depends primarily on the hydronium ion generated in the first ionization step.
Same principle is applied for conjugate bases of polyprotic acids.
Phosphoric acid:
First ionization step: Ka1 =
Second ionization step: Ka2 =
Third ionization step: Ka3 =

59. Lewis Acids and Bases Gilbert N Lewis (1930s)
Lewis acid is a substance that can a pair of electrons from another atom to form a new bond.
Lewis base is a substance that can a pair of electrons to another atom to form a new bond.
A + B: BA
acid
base
acid-base adduct
coordinate covalent bond

60. Cationic Lewis Acids
Complex ions or Coordination complexes (due to coordinate covalent bond).
[Fe(H2O)6]3+ ; [Co(H2O)6]2+; [Cu(H2O)6]2+; [Cu(NH3)4]2+
OH- is a Lewis base
Amphoteric substance: metal hydroxide that can behave as an acid or a base: Al(OH)3
Al(OH)3 (s) + OH- (aq) [Al(OH)4]- (aq)
Al(OH)3 (s) + 3 H3O+ (aq) Al3+ (aq) + 6 H2O (l)

61. Molecular Lewis Acids CO2 (g) + OH- (l) HCO3- (aq)
Explains why nonmetals behave as _______.
C in CO2 is slightly positive, a negatively charged Lewis base OH- can attack this atom to give bicarbonate ion:
CO2 (g) + OH- (l) HCO3- (aq)
Substances which lone pairs of electrons (central atom) can behave as Lewis _______. Substances which lack an electron pair behave as a Lewis _______.

62. Remember Go over all the contents of your textbook.
Practice with examples and with problems at the end of the chapter.
Practice with OWL.
Work on your OWL assignment for Chapter 17.