1. Acid-Base Equilibria

2. Arrhenius acids increase [H+] when dissolved in water
acids can be classified as monoprotic, diprotic or triprotic
bases increase [OH-] when dissolved in water
bases can be classified as monobasic, dibasic, or tribasic

3. A-B Strength
strong acids & bases ionize completely and are strong electrolytes
7 acids & 8 bases (memorize them!!!)
diprotic acids & dibasic bases do NOT ionize completely, only their first H+ or OH- ionizes completely.
Strong acid + strong base = neutral salt
strong A-B are not equilibrium expressions, but all other A-B are reversible

4. Bronsted-Lowry A-B restricts definition to H+
acids donate H+
bases accept H+
allows the classification of less traditional A-B
conjugate A-B pairs = 2 formulas in an equation whose formulas differ by a H+

5. What is the acid, base, and the conjugates?
HClO +H2O H3O+ + ClO- CO32- + H2O OH- + HCO3-

6. Wait, water can go both ways?
amphoteric substances can behave as either an acid or base depending on what they react with.
water and anions with protons (H+) attached are most common amphoterics

7. Weak A-B only partially ionize in water and are weak electrolytes
can be written as equilibrium expressions with a Ka or Kb value
K value indicates how much the acid or base will ionize (high K = higher ionization)
larger K values indicate a stronger acid or base
For di- and tri- protic/basic, there will be 2 K values (one for the first ionization and one for the second)

8. Autoionization of Water
H2O + H2O OH- + H3O+
reversible equilibrium where water can donate a proton to itself
Kw = 1.0 x at room temp.
For any conjugate A-B pair, Kw = Ka x Kb
What is the Ka value for NH4+?

9. Example
Is an aqueous solution of Na2HPO4 acidic or basic?

10. pH scale
pH = -log[H+]
works for pH ranges from 2-12 and approximates pH outside that window
The exponent on the [H+] is an indicator of approximate pH.

12. Strong A-B no equilibrium b/c all acid/base ionizes
use original acid concentration to calculate pH
Calculate the [H+] and pH in a solution of 0.37M hydrochloric acid.
Calculate the [OH-] and pH in a 0.58M solution of NaOH

13. Weak Acids use RICE to find equilibrium concentrations:
R HA + H2O H3O+ + A-
I I
C -x x +x
E I-x x x
b/c Ka for most weak acids is less than 10-3, I-x is about equal to I, so Ka = x2/I

14. Example
What is the pH of a 0.20M solution of acetic acid (CH3COOH)?

15. Weak Bases similar calculations as acids (replace H3O+ with OH-)
R B + H2O OH- + HB+
I I
C -y y +y
E I-y y y
b/c Kb for most weak bases is less than 10-3, I-y is about equal to I, so Kb = y2/I

16. Example
What is the pH of a 0.68M solution of aqueous ammonia?

17. Classify the following as weak/strong acids/bases:
chloric acid
ammonium chloride
calcium hydroxide
ethyl amine
sodium cyanide

18. Example
Measurements show that the pH of a 0.10M solution of acetic acid is What is the Kb of potassium acetate?

19. A-B properties of salt solutions
for the most part anions are slightly basic (because they attract protons) and cations are slightly acidic (because they can donate protons)
ions from strong A-B are the only neutral ions
To determine if a salt is acidic or basic, look at the ions it forms:
ignore any neutral ions
if anion is left, salt is basic
if cation is left, salt is acidic
if both cation & anion are neutral, salt is neutral
if both cation & anion are not neutral, the A-B-ness can’t be determined from the formula

20. Classify the following salts as acidic, basic, or neutral:
NaNO2
CH3NH3Cl
NaCl
MgSO4
Al2(SO3)3

21. A-B-ness & chemical structure
3 factors affect attraction of electrons (acidity increases with stronger attraction of electrons)
ionic charge – when comparing similar atoms, more positive ions are stronger acids
oxidation # on central atom – when comparing similar formulas with the same central atom, the higher the ox#, the stronger the acid
electronegativity – when comparing similar formulas with different central atoms, the higher the EN, the stronger the acid

22. Common Base Reactions
Strong bases also include hydrides (H-), nitrides (N3-), and carbides (C22-)
NaH + H2O  H2 + Na+ + OH-
Mg3N2 + 6H2O  2NH3 + 3Mg2+ + 6OH-
Ca2C2 + 2H2O  C2H2 + Ca2+ + 2OH-
strong bases also include oxides of groups 1&2 metals
Li2O + H2O  2Li+ + 2OH-
CaO + H2O  Ca2+ + 2OH-

23. Common Acid Reactions
nonmetal oxides (aka. acid anhydrides) turn into acids when placed in water
SO2 + H2O H2SO3
CO2 + H2O H2CO3
Cl2O7 + H2O  2H+ + 2ClO4-