1. CHM 101
Sinex
Acids and Bases
Ch. 19

2. General Properties ACIDS Taste sour Turn litmus
CHM 101
Sinex
General Properties
ACIDS
Taste sour
Turn litmus
React with active metals – Fe, Zn to form Hydrogen gas
React with bases
BASES
Taste bitter
Turn litmus
Feel soapy or slippery (react with fats to make soap)
React with acids
blue to red
red to blue

3. Definitions Acids – produce H+ Bases - produce OH- Acids – donate H+
CHM 101
Sinex
Definitions
Acids – produce H+
Bases - produce OH-
Acids – donate H+
Bases – accept H+
Acids – accept e- pair
Bases – donate e- pair
Arrehenius
only in water
Bronsted-Lowry
any solvent
Lewis
used in organic chemistry,
wider range of substances

4. Acid A substance that donates (gives up) H+ ions
CHM 101
Sinex
Acid
A substance that donates (gives up) H+ ions
Ex: HCl + H2O H+ + Cl- + H2O
High concentration of H+ ions
On the pH table:
0 ≈ strong acid
6.9 ≈ weak acid
A note about hydronium ion (H3O+): in water H+ H3O+ so they are the same thing!!!

5. Base A substance that accepts (bonds with) H+ ions
CHM 101
Sinex
Base
A substance that accepts (bonds with) H+ ions
Ex: NaOH + H+ Na+ + H2O
Low concentration of H+ ions (they all bonded)
On the pH table:
14 ≈ strong base
7.1 ≈ weak base

6. Acids and bases come in pairs
CHM 101
Sinex
Acids and bases come in pairs
General equation is:
HX(aq) + H2O(l) ↔ H3O+(aq) + X-(aq)
Acid + Base ↔ Conjugate + Conjugate acid base
Ex: HCl + NaOH ↔ H2O

7. Acids and bases come in pairs
CHM 101
Sinex
Acids and bases come in pairs
A “conjugate base” is the remainder of the original acid, after it donates it’s hydrogen ion
A “conjugate acid” is the particle formed when the original base gains a hydrogen ion

8. Water: acid or base? NH3 + H2O ↔ NH41+ + OH1- base acid c.a. c.b.
CHM 101
Sinex
Water: acid or base?
NH3 + H2O ↔ NH41+ + OH1-
base acid c.a c.b.
HCl + H2O ↔ H3O1+ + Cl1-
acid base c.a c.b.

9. Strong and Weak Acids/Bases
CHM 101
Sinex
Strong and Weak Acids/Bases
Strong acids/bases – 100% dissociation into ions
HCl NaOH
HNO3 KOH
H2SO4
Weak acids/bases – partial dissociation, both ions and molecules
CH3COOH NH3

10. Let’s examine the behavior of an acid, HX, in aqueous solution.
CHM 101
Let’s examine the behavior of an acid, HX, in aqueous solution.
Sinex HX
What happens to the HX molecules in solution?

11. 100% dissociation of HX HX H+ Strong Acid X-
CHM 101
Sinex
100% dissociation of HX HX H+
Strong Acid X-
Would the solution be conductive?

12. Partial dissociation of HX
CHM 101
Sinex
Partial dissociation of HX HX H+
Weak Acid X-
Would the solution be conductive?

13. At any one time, only a fraction of the molecules are dissociated.
CHM 101
Sinex
HX  H X- HX H+
Weak Acid X-
At any one time, only a fraction of the molecules are dissociated.

14. Measuring strength Ionization is reversible: HX + H2O ↔ H+ + X-
CHM 101
Sinex
Measuring strength
Ionization is reversible:
HX + H2O ↔ H+ + X-
This makes an equilibrium
Acid dissociation constant = Ka
Ka = [H+ ][X- ] [HX]
Stronger acid = more products (ions), thus a larger Ka
(Note that the arrow goes both directions.)
(Note that water is NOT shown, because its concentration is constant, and built into Ka)

15. CHM 101
Sinex
What about bases?
Strong bases dissociate completely.
MOH + H2O ↔ M+ + OH- (M = a metal)
Base dissociation constant = Kb
Kb = [M+ ][OH-] [MOH]
Stronger base = more dissociated ions are produced, thus a larger Kb.

16. Neutralization Reaction
CHM 101
Sinex
Neutralization Reaction
In general: Acid Base  Salt + Water
All neutralization reactions are double displacement reactions.
HCl NaOH  NaCl HOH
HCl Mg(OH)2 
H2SO NaHCO3 