1. ACIDS and BASES Chapter 19

2. pH indicators
pH indicators are valuable tool for determining if a substance is an acid or a base.
The indicator will change colors in solution.

3. Things to use…
pH meter will indicate the numeric value of acid or base based on the pH range
Chemical indicators: phenolphthalein, universal indicator…
Natural indicators: poinsettia, red cabbage juice…

4. 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

5. The Arrhenius Theory of Acids and Bases

6. Arrhenius Theory of Acids and Bases:
an acid contains hydrogen and ionizes in solutions to produce H+ ions:
HCl  H+(aq) + Cl-(aq)

7. Arrhenius Theory of Acids and Bases:
a base contains an OH- group and ionizes in solutions to produce OH- ions:
NaOH  Na+(aq) + OH-(aq)

8. Neutralization
Neutralization: the combination of H+ with OH- to form water.
H+(aq) + OH-(aq)  H2O (l)
Hydrogen ions (H+) in solution form hydronium ions (H3O+)

9. In Reality… H+ + H2O  H3O+ Hydronium Ion
(Can be used interchangeably with H+)

10. 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.

11. Bronsted-Lowry Theory of Acids & Bases

12. Bronsted-Lowry Theory of Acids & Bases:
An acid is a proton (H+) donor
A base is a proton (H+) acceptor

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

14. 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

15. 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.

16. 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.

17. Examples: In the following reactions, label the conjugate acid-base pairs:
H3PO4 + NO2-  HNO2 + H2PO4-
CN- + HCO3-  HCN + CO32-
HCN + SO32-  HSO CN-
H2O + HF  F- + H3O+
acid
base
c. acid
c. base
base
acid
c. acid
c. base
acid
base
c. acid
c. base
base
acid
c. base
c. acid

18. 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.
Any substance which accepts a proton.

19. Strength of Acids and Bases
A strong acid dissociates completely in sol’n:
HCl  H+(aq) + Cl-(aq)
A weak acid dissociates only partly in sol’n:
HNO2  H+(aq) + NO2-(aq)
A strong base dissociates completely in sol’n:
NaOH  Na+(aq) + OH-(aq)
A weak base dissociates only partly in sol’n:
NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)

20. Acid-Base Reactions H+(aq) + OH-(aq)  H2O(l)
Neutralization reactions: reactions between acids and metal hydroxide bases which produce a salt and water.
H+ ions and OH- ions combine to form water molecules:
H+(aq) + OH-(aq)  H2O(l)