1. Acids, Bases, and Salts
CHM PGCC Barbara A. Gage

2. Characteristics of Acids and Bases
Litmus color
Phenolphthalein color
pH range
Reaction with active metal (like Mg)
Taste
Formula component
CHM PGCC Barbara A. Gage

3. Acids Strong Weak ionizes completely in water
ionizes partially in water
hydrochloric acid, HCl
hydrofluoric acid, HF
hydrobromic acid, HBr
phosphoric acid, H3PO4
hydroiodic acid, HI
acetic acid, CH3COOH (or HC2H3O2)
nitric acid, HNO3
sulfuric acid, H2SO4
carbonic acid, H2CO3
perchloric acid, HClO4
CHM PGCC Barbara A. Gage

4. The extent of dissociation for strong acids.
Strong acid: HA(g or l) + H2O(l) H3O+(aq) + A-(aq)
H+ and H2O  H3O+ (hydronium ion)
CHM PGCC Barbara A. Gage

5. The extent of dissociation for weak acids.
Weak acid: HA(aq) + H2O(l) H3O+(aq) + A-(aq)
CHM PGCC Barbara A. Gage

6. Bases (or alkalis) Strong Moderate Dissociates completely
Dissociates completely but is not very soluble
sodium hydroxide, NaOH
magnesium hydroxide, Mg(OH)2
potassium hydroxide, KOH
aluminum hydroxide, Al(OH)3
calcium hydroxide, Ca(OH)2
Weak
strontium hydroxide, Sr(OH)2
barium hydroxide, Ba(OH)2
Dissociates partially
ammonia, NH3 (NH4OH)
carbonates, CO32-
bicarbonates, HCO31-
CHM PGCC Barbara A. Gage

7. An aqueous strong acid-strong base reaction on the atomic scale.
MX is a “salt” – an electrolyte that is not an acid or base
CHM PGCC Barbara A. Gage

8. Acid and Base Definitions
Arrhenius
Acid = compound that forms hydrogen (H+) ions in water
Base = compound that forms hydroxide (OH-) ions in water
CHM PGCC Barbara A. Gage

9. Acid and Base Definitions
Bronsted-Lowry
Acid = proton donor (H+ is a proton)
Base = proton acceptor
An acid-base reaction can now be viewed from the standpoint of the reactants AND the products.
An acid reactant will produce a base product and the two will constitute an acid-base conjugate pair.
CHM PGCC Barbara A. Gage

10. Proton transfer as the essential feature of a Brønsted-Lowry acid-base reaction.
Lone pair binds H+
HCl
H2O +
Cl-
H3O+ +
(acid, H+ donor)
(base, H+ acceptor)
NH3
H2O +
Lone pair binds H+
NH4+
OH- +
(base, H+ acceptor)
(acid, H+ donor)
CHM PGCC Barbara A. Gage

11. The Conjugate Pairs in Some Acid-Base Reactions+
Base
Acid +
Conjugate Pair
Reaction 1 HF
H2O + F-
H3O+ +
Reaction 2
HCOOH
CN- +
HCOO-
HCN +
Reaction 3
NH4+
CO32- +
NH3
HCO3- +
Reaction 4
H2PO4-
OH- +
HPO42-
H2O +
Reaction 5
H2SO4
N2H5+ +
HSO4-
N2H62+ +
Reaction 6
HPO42-
SO32- +
PO43-
HSO3- +
CHM PGCC Barbara A. Gage

12. Identifying Conjugate Acid-Base Pairs
SAMPLE PROBLEM
Identifying Conjugate Acid-Base Pairs
PROBLEM:
The following reactions are important environmental processes. Identify the conjugate acid-base pairs.
(a) H2PO4-(aq) + CO32-(aq) HPO42-(aq) + HCO3-(aq)
(b) H2O(l) + SO32-(aq) OH-(aq) + HSO3-(aq)
Identify proton donors (acids) and proton acceptors (bases).
conjugate pair2
conjugate pair1
SOLUTION:
(a) H2PO4-(aq) + CO32-(aq) HPO42-(aq) + HCO3-(aq)
proton donor
proton acceptor
proton acceptor
proton donor
conjugate pair2
conjugate pair1
(b) H2O(l) + SO32-(aq) OH-(aq) + HSO3-(aq)
proton donor
proton acceptor
proton acceptor
proton donor
CHM PGCC Barbara A. Gage

13. Molecules as Lewis Acids
An acid is an electron-pair acceptor.
A base is an electron-pair donor.
acid
base
adduct
H2O(l)
M(H2O)42+(aq)
M2+
adduct
CHM PGCC Barbara A. Gage

14. Identifying Lewis Acids and Bases
SAMPLE PROBLEM
Identifying Lewis Acids and Bases
PROBLEM:
Identify the Lewis acids and Lewis bases in the following reactions:
(a) H+ + OH H2O
(b) Cl- + BCl BCl4-
(c) K+ + 6H2O K(H2O)6+
PLAN:
Look for electron pair acceptors (acids) and donors (bases).
SOLUTION:
acceptor
(a) H+ + OH H2O
donor
donor
(b) Cl- + BCl BCl4-
acceptor
acceptor
(c) K+ + 6H2O K(H2O)6+
donor
CHM PGCC Barbara A. Gage

15. Acid Anhydrides
Non-metal oxides react with water to form acidic solutions
CO2 (g) H2O (l)  H2CO3 (aq)
N2O5 (s) + H2O (l)  2 HNO3 (aq)
SO3 (g) H2O (l)  H2SO4 (aq)
Dissolved non-metal oxides cause acid rain.
CHM PGCC Barbara A. Gage

16. Basic Anhydrides
Metal oxides react with water to form alkaline solutions
Na2O (s) H2O (l)  2 NaOH (aq)
CaO (s) H2O (l)  Ca(OH)2 (aq)
Al2O3 (s) H2O (l)  2 Al(OH)3 (aq)
Lime (CaO) is used on lawns and is converted to Ca(OH)2 when it rains. CaO is less hazardous to handle.
CHM PGCC Barbara A. Gage

17. Point of neutralization
An acid-base titration.
Start of titration
Excess of acid
Point of neutralization
Slight excess of base
CHM PGCC Barbara A. Gage

18. Finding the Concentration of Acid from an Acid-Base Titration
Sample Problem
Finding the Concentration of Acid from an Acid-Base Titration
PROBLEM:
You perform an acid-base titration to standardize an HCl solution by placing mL of HCl in a flask with a few drops of indicator solution. You put M NaOH into the buret, and the initial reading is 0.55 mL. At the end point, the buret reading is mL. What is the concentration of the HCl solution?
SOLUTION:
NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l)
( ) mL x 1L
103 mL
= L L
X M
= 5.078x10-3 mol
NaOH
Molar ratio is 1:1
5.078x10-3 mol HCl L
= M HCl
CHM PGCC Barbara A. Gage

19. H2O(l) + H2O(l) H3O+(aq) + OH-(aq)
Kc =
[H3O+][OH-]
[H2O]2
The Ion-Product Constant for Water
Kc[H2O]2 =
Kw =
[H3O+][OH-]
= 1.0 x at 250C
A change in [H3O+] causes an inverse change in [OH-].
In an acidic solution, [H3O+] > [OH-]
In a basic solution, [H3O+] < [OH-]
In a neutral solution, [H3O+] = [OH-]
CHM PGCC Barbara A. Gage

20. The relationship between [H3O+] and [OH-] and the
relative acidity of solutions.
Divide into Kw
[H3O+]
[OH-]
[H3O+] > [OH-]
[H3O+] = [OH-]
[H3O+] < [OH-]
ACIDIC SOLUTION
NEUTRAL SOLUTION
BASIC SOLUTION
CHM PGCC Barbara A. Gage

21. Calculating [H3O+] and [OH-] in an Aqueous Solution
SAMPLE PROBLEM
Calculating [H3O+] and [OH-] in an Aqueous Solution
PROBLEM:
A research chemist adds a measured amount of HCl gas to pure water at 250C and obtains a solution with [H3O+] = 3.0x10-4M. Calculate [OH-]. Is the solution neutral, acidic, or basic?
Use the Kw at 250C and the [H3O+] to find the corresponding [OH-].
SOLUTION:
Kw = 1.0x10-14 = [H3O+] [OH-] so
[OH-] = Kw/ [H3O+] = 1.0x10-14/3.0x10-4 =
3.3x10-11M
[H3O+] is > [OH-] and the solution is acidic.
CHM PGCC Barbara A. Gage

22. The pH values of some familiar aqueous solutions.
pH = -log [H3O+]
pOH = -log [OH-]
pH + pOH = 14
CHM PGCC Barbara A. Gage

23. The relations among [H3O+], pH, [OH-], and pOH.
CHM PGCC Barbara A. Gage

24. Calculating [H3O+], pH, [OH-], and pOH
SAMPLE PROBLEM
Calculating [H3O+], pH, [OH-], and pOH
PROBLEM:
In an art restoration project, a conservator prepares copper-plate etching solutions by diluting concentrated HNO3 to 2.0M, 0.30M, and M HNO3. Calculate [H3O+], pH, [OH-], and pOH of the three solutions at 250C.
PLAN:
HNO3 is a strong acid so [H3O+] = [HNO3]. Use Kw to find the [OH-] and then convert to pH and pOH.
SOLUTION:
For 2.0M HNO3, [H3O+] = 2.0M and -log [H3O+] = = pH
[OH-] = Kw/ [H3O+] = 1.0x10-14/2.0 = 5.0x10-15M; pOH = 14.30
For 0.3M HNO3, [H3O+] = 0.30M and -log [H3O+] = 0.52 = pH
[OH-] = Kw/ [H3O+] = 1.0x10-14/0.30 = 3.3x10-14M; pOH = 13.48
For M HNO3, [H3O+] = M and -log [H3O+] = 2.20 = pH
[OH-] = Kw/ [H3O+] = 1.0x10-14/6.3x10-3 = 1.6x10-12M; pOH = 11.80
CHM PGCC Barbara A. Gage

25. Buffers Solutions that resist change in pH
Can maintain any pH value between 0 and 14 (not just neutral pH 7)
Composed of a weak acid and a salt made from the weak acid or weak base and salt made from the weak base
Examples: HC2H3O2 and NaC2H3O2
NH4OH and NH4Cl
CHM PGCC Barbara A. Gage

26. Buffers Reaction with acid: HC2H3O2 + C2H3O2- + H+  HC2H3O2 + HC2H3O2
Reaction with base:
HC2H3O2 + C2H3O2- + OH- 
C2H3O2- + C2H3O2- + HOH
A buffer regenerates it’s own components. The pH it maintains depends on the ratio of salt to acid (or base) and the nature of the acid (or base).
CHM PGCC Barbara A. Gage