1. NOTES: 19.1 – Acid-Base Theories

2. Acids & Bases have distinctive properties…

3. Properties of Acids and Bases
● Have a sour taste
● Change the color of many indicators
● Are corrosive (react with metals)
● Neutralize bases
● Conduct an electric current
BASES
● Have a bitter taste
● Change the color of many indicators
● Have a slippery feeling
● Neutralize acids
● Conduct an electric current

4. The Arrhenius Theory of Acids and Bases

5. Acids & Bases – Arrhenius Theory
● An acid is a compound that contains an H+, and produces hydrogen ion (H+) when dissolved in water.
Example: HCl  H+ + Cl-

6. In Reality… HCl + H2O  H3O+(aq) + Cl-(aq) Hydronium Ion
(can be used interchangeably with H+)

7. Acids & Bases – Arrhenius Theory
● A base is a compound that contains an OH- group and produces hydroxide ions (OH-) when dissolved in water.
Example: NaOH  Na+ + OH-

8. Neutralization
● Neutralization: the combination of H+ with OH- to form water. ● H+(aq) + OH-(aq)  H2O(l)

9. Commentary on Arrhenius Theory…
One problem with the Arrhenius theory is that it’s not comprehensive enough. Some compounds act like acids and bases that don’t fit the standard definition.

10. Bronsted-Lowry Theory of Acids & Bases

11. Bronsted-Lowry Theory of Acids & Bases:
● An ACID is a proton (H+) donor ● A BASE is a proton (H+) acceptor

12. for example… Proton transfer HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)
Base
Acid

13. another example… Water is a proton donor, and thus an acid.
CONJUGATE BASE
ACID
NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)
BASE
CONJUGATE ACID
Ammonia is a proton acceptor, and thus a base

14. Conjugate acid-base pairs
● Conjugate acid-base pairs differ by one proton (H+)
**A conjugate acid is the particle formed when a base gains a proton.
**A conjugate base is the particle that remains when an acid gives off a proton.

15. Examples: In the following reactions, label the conjugate acid-base pairs:
H3PO4 + NO2-  HNO2 + H2PO4-
CN- + HCO3-  HCN + CO32-
acid
base
c. acid
c. base
base
acid
c. acid
c. base

16. Examples: In the following reactions, label the conjugate acid-base pairs:
HCN + SO32-  HSO CN-
H2O + HF  F H3O+
acid
base
c. acid
c. base
base
acid
c. base
c. acid

17. Amphoteric Substances
● A substance that can act as both an acid and a base (depending on what it is reacting with) is termed AMPHOTERIC.
**Water is a prime example.

18. The Lewis Theory of Acids and Bases

19. The Lewis Theory of Acids & Bases
● Lewis acid: a substance that can accept an electron pair to form a covalent bond (electron pair acceptor).
● Lewis base: a substance that can donate an electron pair to form a covalent bond (electron pair donor).

20. Example 1: .. .. .. .. .. Ionization of NH3: NH3 + H2O  NH4+ + OH-
base
acid + H .. H .. - .. ..  .. H N H + H O H H N H + O H H

21. Example 2:
Auto-ionization of water: H2O + H2O  H3O+ + OH- +
acid
base .. .. .. .. - .. ..  .. H O H + H O H H O H + O H H

22. Example 3:
Reaction of NH3 with HBr (a Lewis AND a Bronsted-Lowry acid-base reaction): NH3 + HBr  NH4+ + Br-
base
acid + .. .. H H - .. ..  .. H N H + H Br H N H + Br H

23. Acid Base Theories
Lewis
Bronsted-Lowry
Arrhenius

24. SUMMARY OF ACID-BASE THEORIES:
Theory
Acid Definition
Base Definition
Arrhenius Theory
Any substance which releases H+ ions in water solution.
Any substance which releases OH- ions in water solution
Brǿnsted-Lowry Theory
Any substance which donates a proton (H+).
Any substance which accepts a proton (H+).
Lewis Theory
Any substance which can accept an electron pair.
Any substance which can donate an electron pair.