1. ACIDS AND BASES

2. Section 18.1 Introduction to Acids and Bases
Identify the physical and chemical properties of acids and bases.
Classify solutions as acidic, basic, or neutral.
Compare the Arrhenius and Brønsted-Lowry models of acids and bases.
Different models help describe the behavior of acids and bases.
Section 18-1

3. Some common acids: Sulfuric acid, H2SO4 Hydrochloric acid, HCl
Nitric acid, HNO3
Carbonic acid, H2CO3
Phosphoric acid, H3PO4
Acetic acid, HC2H3O2

4. Some common bases: Sodium hydroxide, NaOH Calcium hydroxide, Ca(OH)2
Potassium hydroxide, KOH
Magnesium hydroxide,Mg(OH)2
Aluminum hydroxide, Al(OH)3
Ammonia, NH3

5. The Arrhenius Model
The Arrhenius model states that an acid is a substance that contains hydrogen and ionizes to produce hydrogen ions in aqueous solution, and a base is a substance that contains a hydroxide group and dissociates to produce a hydroxide ion in solution.
Section 18-1

6. The Arrhenius Model (cont.)
Arrhenius acids and bases
HCl ionizes to produce H+ ions.
HCl(g) → H+(aq) + Cl–(aq)
NaOH dissociates to produce OH– ions.
NaOH(s) → Na+(aq) + OH–(aq)
Some solutions produce hydroxide ions even though they do not contain a hydroxide group.
Section 18-1

7. Properties of Acids and Bases (cont.)
The usual solvent for acids and bases is water—water produces equal numbers of hydrogen and hydroxide ions in a process called self-ionization.
H2O(l) + H2O(l) ↔ H3O+(aq) + OH–(aq)
The hydronium ion is H3O+.
Section 18-1

8. Properties of Acids and Bases (cont.)
All water solutions contain hydrogen ions (H+) and hydroxide ions (OH–).
An acidic solution contains more hydrogen ions than hydroxide ions.
A basic solution contains more hydroxide ions than hydrogen ions.
Section 18-1

9. The Brønsted-Lowry Model
The Brønsted-Lowry Model of acids and bases states that an acid is a hydrogen ion donor, and a base is a hydrogen ion acceptor.
The Brønsted-Lowry Model is a more inclusive model of acids and bases.
Section 18-1

10. The Brønsted-Lowry Model (cont.)
A conjugate acid is the species produced when a base accepts a hydrogen ion.
A conjugate base is the species produced when an acid donates a hydrogen ion.
A conjugate acid-base pair consists of two substances related to each other by donating and accepting a single hydrogen ion.
Section 18-1

11. The Brønsted-Lowry Model (cont.)
Hydrogen fluoride—a Brønsted-Lowry acid
HF(aq) + H2O(l) ↔ H3O+(aq) + F–(aq)
HF = acid, H2O = base, H3O+ = conjugate acid, F– = conjugate base
Section 18-1

12. The Brønsted-Lowry Model (cont.)
Ammonia— Brønsted-Lowry base
NH3(aq) + H2O(l) ↔ NH4+(aq) + OH–(aq)
NH3 = base, H2O(l) = acid, NH4+ = conjugate acid, OH– = conjugate base
Substances that can act as acids or bases are called amphoteric.
Section 18-1

13. Water is amphoteric: HCl + H2O  H3O+ + Cl-1 NH3 + H2O  NH4+1 + OH-
Acts as both an acid and a base
Water is amphoteric:
HCl + H2O  H3O+ + Cl-1
Proton acceptor
NH3 + H2O  NH OH-
Proton donor

14. HCl + SO3-2  HSO Cl-
CONJUGATE ACID
CONJUGATE BASE
ACID
BASE

15. NH3 + HNO2  NO NH4+
CONJUGATE BASE
BASE
CONJUGATE ACID
ACID

16. Monoprotic and Polyprotic Acids
An acid that can donate only one hydrogen ion is a monoprotic acid.
Only ionizable hydrogen atoms can be donated.
Section 18-1

17. Monoprotic and Polyprotic Acids (cont.)
Acids that can donate more than one hydrogen ion are polyprotic acids.
Section 18-1

18. Properties of Acids Acids are proton (hydrogen ion, H+) donors
Acids have a pH lower than 7
Acids taste sour
Acids effect indicators
Blue litmus turns red
Methyl orange turns red
Acids react with active metals, producing H2
Acids react with carbonates
Acids neutralize bases

19. Acids Effect Indicators
Blue litmus paper turns red in contact with an acid.
Methyl orange turns red with addition of an acid

20. Acids React with Active Metals
Acids react with active metals to form salts and hydrogen gas.
Mg + 2HCl  MgCl2 + H2(g)
Zn + 2HCl  ZnCl2 + H2(g)
Mg + H2SO4  MgSO4 + H2(g)

21. Acids React with Carbonates
2HC2H3O2 + Na2CO3
2 NaC2H3O2 + H2O + CO2

22. Effects of Acid Rain on Marble (calcium carbonate)
George Washington:
BEFORE
George Washington:
AFTER

23. Properties of Bases Bases are proton (hydrogen ion, H+) acceptors
Bases have a pH greater than 7
Bases taste bitter
Bases effect indicators
Red litmus turns blue
Phenolphthalein turns purple
Solutions of bases feel slippery
Bases neutralize acids

24. Bases Effect Indicators
Red litmus paper turns blue in contact with a base.
Phenolphthalein turns bright pink in a base.

25. A B C D Section 18.1 Assessment A conjugate acid is formed when:
A. a base accepts a hydrogen ion
B. an acid accepts a hydrogen ion
C. an acid donates a hydrogen ion
D. a base donates a hydrogen ion A B C D
Section 18-1