1. Acids and Bases Chapter 14
DE Chemistry
Dr. Walker

2. Acid – Base Terminology
Arrhenius
Acids produce hydrogen ions in aqueous solutions
Based produce hydroxide ions in aqueous solutions
Bronsted-Lowry
Acids are proton donors
Bases are proton acceptors
Lewis
Acids are electron pair acceptors
Bases are electron pair donors

3. Conjugate Acids and Bases
HCl + H2O Cl- + H3O+ Acid Base Conjugate Conjugate Base Acid Conjugate Base – Formed when acid loses a proton Conjugate Acid – Formed when base gains a

4. Acid Dissociation
HA H A-
Acid Proton Conjugate Base

5. Acid Dissociation HA H+ + A- Acid Proton Conjugate Base
-Based on equilbirium constants from last chapter
-Ka is very high for strong acids, lower for weak acids

6. Dissociation of Strong Acids
Strong acids are assumed to dissociate completely in solution.
Large Ka or small Ka?
Reactant favored or product favored?

7. Dissociation Constants: Strong Acids
Formula
Conjugate Base Ka
 Perchloric 
 HClO4 
 ClO4- 
 Very large 
 Hydriodic 
 HI 
 I- 
 Hydrobromic 
 HBr 
 Br- 
 Hydrochloric 
 HCl 
 Cl- 
 Nitric 
 HNO3 
 NO3- 
 Sulfuric 
 H2SO4 
 HSO4- 
 Hydronium ion 
 H3O+ 
 H2O 
 1.0 

8. Dissociation of Weak Acids
Weak acids are assumed to dissociate only slightly (less than 5%) in solution.
Large Ka or small Ka?
Reactant favored or product favored?

9. Strong and Weak Acids/Bases
Strong Acid – dissociates completely in solution
-Notice the HCl completely breaks apart
-Tends to be smaller molecules
Weak Acid – dissociates partially in solution
Notice the acetic acid stays mostly intact
-Tends to be larger, organic molecules

10. Dissociation Constants: Weak Acids
Formula
Conjugate Base Ka
 Iodic 
 HIO3 
 IO3- 
 1.7 x 10-1 
 Oxalic 
 H2C2O4 
 HC2O4- 
 5.9 x 10-2 
 Sulfurous 
 H2SO3 
 HSO3- 
 1.5 x 10-2 
 Phosphoric 
 H3PO4 
 H2PO4- 
 7.5 x 10-3 
 Citric 
 H3C6H5O7 
 H2C6H5O7- 
 7.1 x 10-4 
 Nitrous 
 HNO2 
 NO2- 
 4.6 x 10-4 
 Hydrofluoric 
HF 
 F- 
 3.5 x 10-4 
 Formic 
 HCOOH 
 HCOO- 
 1.8 x 10-4 
 Benzoic 
 C6H5COOH 
 C6H5COO- 
 6.5 x 10-5 
 Acetic 
 CH3COOH 
 CH3COO- 
 1.8 x 10-5 
 Carbonic 
 H2CO3 
 HCO3- 
 4.3 x 10-7 
 Hypochlorous 
 HClO 
 ClO- 
 3.0 x 10-8 
 Hydrocyanic 
 HCN 
 CN- 
 4.9 x 10-10 
Lower Ka = less dissociation = weaker acid!!!

11. Acid Terminology
Polyprotic – Acids with more than one ionizable proton
Monoprotic - one acidic proton (HCl)
Diprotic - two acidic protons (H2SO4)
Triprotic - three acidic protons (H3PO4)
Oxyacids - acids in which the acidic proton is attached to an oxygen atom (HClO3)
Ionizable
Hydrogen

12. Polyprotic Acids
When multiple acidic protons are present, the removal of each one gives a different equilibrium constant
The first one will always have the highest (strongest) equilibrium constant

13. Acid Terminology
Organic acids - acids containing the mildly acidic carboxyl group
Generally weak acids
Equilibrium lies far to the left (weak acids)

14. Self-Ionization of Water
H2O + H2O H3O+ + OH-
This happens in every glass of water
This occurs in low enough concentration that it is not noticeable
[H3O+] = [OH-] = 1.0 x 10-7 M
[H3O+] [OH-] = 1.0 x M

15. Dissociation of Strong Bases
MOH(s)  M+(aq) + OH-(aq)
Strong bases are metallic hydroxides
Group I hydroxides (NaOH, KOH) are very soluble
Group II hydroxides (Ca, Ba, Mg, Sr) are less soluble
pH of strong bases is calculated directly from the concentration of the base in solution

16. Calculating pH, pOH
pH = -log[H3O+]
pOH = -log[OH-]
Relationship between pH and pOH
pH + pOH = 14
Finding [H3O+], [OH-] from pH, pOH
[H3O+] = 10-pH
[OH-] = 10-pOH

17. The pH scale – Examples of everyday items

18. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of acetic acid, HC2H3O2, Ka = 1.8 x 10-5 ?
Step #1: Write the dissociation equation
HC2H3O2  C2H3O2- + H+

19. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of acetic acid, HC2H3O2, Ka = 1.8 x 10-5 ?
Step #2: ICE it!
HC2H3O2  C2H3O2- + H+ I C E
0.50
- x +x +x x x x

20. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of acetic acid, HC2H3O2, Ka = 1.8 x 10-5 ?
Step #3: Set up the law of mass action
HC2H3O2  C2H3O2- + H+ E x x x
For weak acids, dissociation is small enough that
It is assumed that a weak acid (acetic acid, here), dissociates less than 5%

21. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of acetic acid, HC2H3O2, Ka = 1.8 x 10-5 ?
Step #4: Solve for x, which is also [H+]
HC2H3O2  C2H3O2- + H+ E x x x
[H+] = 3.0 x 10-3 M

22. A Weak Acid Equilibrium Problem
What is the pH of a 0.50 M solution of acetic acid, HC2H3O2, Ka = 1.8 x 10-5 ?
Step #5: Convert [H+] to pH
HC2H3O2  C2H3O2- + H+ E x x x

23. Reaction of Weak Bases with Water
The base reacts with water, producing its conjugate acid and hydroxide ion:
CH3NH2 + H2O  CH3NH3+ + OH- Kb = 4.38 x 10-4

24. Kb for Some Common Weak Bases
Many students struggle with identifying weak bases and their conjugate acids. What patterns do you see that may help you?
Base
Formula
Conjugate Acid Kb
Ammonia 
 NH3
 NH4+
 1.8 x 10-5 
 Methylamine
 CH3NH2
 CH3NH3+
 4.38 x 10-4 
 Ethylamine
 C2H5NH2
 C2H5NH3+
 5.6 x 10-4 
 Diethylamine
 (C2H5)2NH
 (C2H5)2NH2+
 1.3 x 10-3 
 Triethylamine
  (C2H5)3N
  (C2H5)3NH+
 4.0 x 10-4 
 Hydroxylamine
 HONH2 
 HONH3+  
 1.1 x 10-8 
 Hydrazine
H2NNH2 
H2NNH3+  
 3.0 x 10-6 
 Aniline
 C6H5NH2 
 C6H5NH3+  
 3.8 x 10-10 
 Pyridine
 C5H5N 
 C5H5NH+  
 1.7 x 10-9 

25. A Weak Base Equilibrium Problem
What is the pH of a 0.10 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #1: Write the equation for the reaction
NH3 + H2O  NH4+ + OH-

26. A Weak Base Equilibrium Problem
What is the pH of a 0.10 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #2: ICE it!
NH3 + H2O  NH4+ + OH- I C E
0.10
- x +x +x x x x

27. A Weak Base Equilibrium Problem
What is the pH of a 0.10 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #3: Set up the law of mass action
NH3 + H2O  NH4+ + OH- E x x x

28. A Weak Base Equilibrium Problem
What is the pH of a 0.10 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #4: Solve for x, which is also [OH-]
NH3 + H2O  NH4+ + OH- E x x x
[OH-] = 1.3 x 10-3 M

29. A Weak Base Equilibrium Problem
What is the pH of a 0.10 M solution of ammonia, NH3, Kb = 1.8 x 10-5 ?
Step #5: Convert [OH-] to pH
NH3 + H2O  NH4+ + OH- E x x x

30. Effect of Structure on Acid-Base Properties
Hypochlorous
acid
Chlorous
acid
Chloric
acid
Perchloric
acid
Increasing Acidity (more oxygens)

31. Acid-Base Properties of Oxides
Acidic Oxides (also called acid anhydrides)
Nonmetal oxides that react with water to form acidic solutions
SO3(g) + H2O(l) H2SO4(aq)
2 NO2(g) + H2O(l) HNO3(aq) + HNO2(aq)

32. Acid-Base Properties of Oxides
Basic Oxides (also called basic anhydrides)
Metallic oxides of Group 1A and 2A metals react with water to form basic solutions
K2O(s) + H2O(l) KOH (aq)
CaO(s) + H2O(l) Ca(OH)2(aq)

33. Titrations Type of quantitative analysis
Start with known concentration and volume of a solution, known as a titrant
Titrant can be acid or base
Add to a sample solution with unknown concentration, known as an analyte
Analyte will be the opposite of the titrant
Reaches the endpoint when the indicator turns color
Indicator: Dye that changes color with a change in pH

34. A Titration Pictured
Left: student performing a titration. The titrant is in a long tube called a buret. The analyte is in the Erlenmeyer flask below.
Right: A close-up view of a buret, measuring in 0.1 mL increments.

35. Common Indicators

36. Calculations The most common calculation involves using dilutions
Example: mL of 0.1 M HCl solution is required to titrate 100 mL of a base. What is the concentration of the base?

37. Calculations The most common calculation involves using dilutions
Example: mL of 0.1 M HCl solution is required to titrate 50 mL of a base. What is the concentration of the base?
M1V1 = M2V2
(0.1 M)(32.5 mL) = M2 (50 mL)
M2 = M

38. Titration Curves
Titration curves depict the change in pH versus the amount of titrant (acid or base) added

39. Additional Vocabulary
Equivalence Point – pH where the moles (acid) = moles (base)
Notice the equivalence point depends on the strength of the acid being titrated

40. Titration Curves Notice the difference between the curves
Left: The titration of a strong acid has a sharp curve before reaching the equivalence point
Right: The titration of the weak acid has a shallow curve prior to the equivalence point

41. Polyprotic Acids
Polyprotic acids have multiple Ka values – one for each ionizable proton
Each ionizable proton has a separate equivalence point at a different pH