1. The Nature of Acids and Bases- Acid Strength and Ionization Constant
Chapter

2. Acids and Bases in Nature
Acids (sour in latin) are abundant, and diverse in their functions throughout the natural world.
Citric acid (H3C6H5O7) gives citrus fruit their sour flavour
Acetic Acid (HC2H3O2) is active in vinegar
Hydrochloric acid (HCl) has a variety of uses including refining metal ore and digesting food in our stomachs
Many organic acids contain a Carboxylic acid group
Acids turn blue litmus paper red

3. Acids and Bases in Nature
Characterized by a bitter taste and a slippery feel
Sodium Hydroxide (NaOH) active in soap
Alkaloids, usually present in poisonous plants, and dark chocolate
Sodium Hydroxide (NaOH) and Potassium Hydroxide (KOH) are present in most labs
Household cleaners such as ammonia (NH3) and drāno are basic and are characteristically slippery

4. Arrhenius Definition
Acid: A substance that produces H+ ions in aqueous solution
Base: A substance that produces OH- ions in a solution
Example: HCl is considered an acid
HCl(aq) → H+(aq) + Cl-(aq)
HCl contains a covalent bond but it ionizes completely in water. These H+ ions are highly reactive and bond with water to form Hydronium H3O+

5. Arrhenius continued
Example: NaOH is a base because it produces OH- ions
NaOH(aq) → Na+(aq) +OH- (aq)
NaOH dissociates in into its component ions when it is placed in water
Under the Arrhenius definition, H+ released by acids and OH- released by bases combine to form water, neutralizing each other

6. Quick Review
Based on the Arrhenius Definition of acids and bases, which of the following is a base?
KOH
NH4
H2CO3
In water, KOH readily dissociates into K+ and OH-, producing OH-

7. The Brømsted-Lowry Definition
Acid: Proton (H+ion) donor
Base: Proton (H+ion) acceptor
Examples:
HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq)
NH3(aq) + H2O ⇋ NH4+(aq) + OH-(aq)

8. Surprise, Water is Special
The Brønstead- Lowry definition allows for substances that can act as both acids and bases, Water is one of these amphoteric substances.
NH3(aq) + H2O ⇋ NH4+(aq) + OH-(aq)
Accepts proton
(base)
Donates proton
(acid)
Conjugate acid
Conjugate Base
NH4+(aq) + OH-(aq) ⇋ NH3(aq) + H2O
Donates proton
(acid)
Accepts proton
(base)

9. Practice! Identify the acid and base in the following reactions:
H2SO4(aq) + H2O → HSO4-(aq)+ H3O+(aq)
HCO3-(aq)+ H2O → H2CO3(aq)+OH-(aq)

10. More Practice! Write the conjugate base or acid. HCl ClO4- HCHO2 Cl-
HClO4
CHO2-

11. 15.4: Acid Strength and Ionization Constant (Ka)

12. Strong and Weak Acids
The strength of an acid is determined by the degree to which it will ionize. A strong acid will ionize completely in solution whereas a weak acid will only ionize partially. This depends on equilibrium.
HA(aq) + H2O ⇋ H3O+(aq)+ A-(aq)
This is a generic formula, HA represents the acid and A represents its conjugate base.
Ka<1→ weak acid
Ka>1 → strong acid

13. Examples CH3COOH + H2O ⇋ H3O+ + CH3COO-
Ka = [H3O+][CH3COO-]/ [CH3COOH] = 1.76 x 10-5
W E A K
Carboxylic acids are notorious for being weak
pKa= -logKa = 4.75
Important weak acids to know:
HF, HC2H3O2,HCHO2,H2SO3(di),H2CO3, H3PO4(tri)

14. Example HCl is a strong acid, Ka= 1.3 x 106
Important strong acids to memorize:
HCl, HBr,HI, HNO3, HClO4,H2SO4
Monoprotic acids: those that one contain one ionizable proton
Polyprotic: an acid with 2 ionizable protons

15. Acid Ionization Constant (Ka)
Using our general formula from earlier.
HA(aq) + H2O ⇋ H3O+(aq)+ A-(aq)
HA(aq) ⇋ H+(aq)+ A-(aq)

16. Ionization Constant Practice
Calculate the concentration of ions in a solution of .15M acetic acid (HC2H3O2) and a Ka of 1.8 x 10-5.
3 x 10-6

18. AP expectation