1. Acids and Bases
Dr. Ron Rusay
Fall 2001
© Copyright 2001 R.J. Rusay

2. Introduction to Aqueous Acids
Acids: taste sour and cause certain dyes to change color.

3. Introduction to Aqueous Bases
Bases: taste bitter, feel soapy and cause certain dyes to turn color.

4. Electrolytes
Aqueous solutions can be categorized into 3 types: non-electrolytes, strong electrolytes or weak electrolytes based on their ability to conduct electricity.
A solution must have ions to conduct.
Pure Water does not conduct.
Aqueous solutions can be tested for conductivity which will determine the degree of ionization of the solutes.
It is possible to have full or partial ionization.
© Copyright R.J. Rusay

5. Solution Test Apparatus for Electrolytes

6. Conductivity

7. Electrolytes / Ionization

8. Electrolytes
Almost all ionic compounds and a few molecular compounds are strong electrolytes.
Several molecular compounds are weak conductors, most are non-conductors.
Conductivity is directly related to the amount of ionization, i.e. ions in solution. Table salt, sodium chloride, is completely ionized:
NaCl(s) + H2O(l) ---> NaCl(aq) ---> mol Na +(aq) + Cl -(aq)
0.00mol mol mol
© Copyright R.J. Rusay

9. Strong vs. Weak Electrolytes

10. Models of Acids and Bases
Arrhenius Concept: Acids produce H+ in solution, bases produce OH ion.
Brønsted-Lowry: Acids are H+ donors, bases are proton acceptors.
HCl + H2O  Cl + H3O+
acid base

11. Lewis Acids and Bases Lewis Acid: electron pair acceptor
Lewis Base: electron pair donor

12. Conjugate Acid/Base Pairs
HA(aq) + H2O(l)  H3O+(aq) + A(aq)
conj conj
acid base acid base 2
conjugate base: everything that remains of the acid molecule after a proton is lost.
conjugate acid: formed when the proton is transferred to the base.

13. Acid Strength Strong Acids:
100% of the acid is ionized. For example nitric acid, HNO3 , produces 100% H+ (aq). Other common strong acids are sulfuric and hydrochloric.
Stong acids produce very weak conjugate bases, eg. (NO3)

14. Dissociation of Strong and Weak Acids

15. Acid Strength (continued)
Weak Acids:
A weak acid is not 100% ionized. For example acetic acid, CH3COOH, produces <100% H+ (aq). Most acids, particularly organic acids, are weak acids.
Weak acids produce a much stronger conjugate base than water, eg. The acetate ion: (CH3COO)

17. Aqueous Bases NH3 (g) + H2O(l) NH3 (aq) NH4+(aq)+ OH-(aq)
Any compound that accepts a proton is a base.
The common bases are group IA & IIA metal hydroxide compounds. “Strong” and “weak” are used in the same sense for bases as for acids.
Strong = complete dissociation (100% hydroxide ion is supplied to the solution) An example of a weak base is ammonia.
NH3 (g) + H2O(l) NH3 (aq) NH4+(aq) OH-(aq)
© Copyright R.J. Rusay

18. H3CNH2(aq) + H2O(l)  H3CNH3+(aq) + OH(aq)
Bases (continued)
Weak bases have very little dissociation (or reaction with water), eg. methyl amine has <100% hydroxide ion in aqueous solution.
H3CNH2(aq) + H2O(l)  H3CNH3+(aq) + OH(aq)
Organic bases are weak bases; for example, dopamine (neurotransmitter), cadaverine (product of cellular decomposition) and morphine (narcotic pain killer) are weak bases.

19. Water as an Acid and a Base
Water is amphoteric (it can behave either as an acid or a base).
H2O + H2O  H3O+ + OH
conj conj
acid 1 base acid base 2
Kw = 1  1014 at 25°C

20. Water: Self-ionization

21. pH  log[H+]  log[H3O+]
The pH Scale
pH  log[H+]  log[H3O+]
pH in water ranges from 0 to 14.
Kw = 1.00  1014 = [H+] [OH]
pKw = = pH + pOH
As pH rises, pOH falls (sum = 14.00).
There are no theoretical limits on the values of pH or pOH. (e.g. pH of 2.0 M HCl is , the pH at Iron Mountain is ~ -2 to -3)

23. The pH of Some Familiar Aqueous Solutions [H3O+] [OH-] [OH-] = KW
acidic
solution
neutral
solution
basic
solution
[H3O+] =
[OH-]

24. Natural Indicators

25. The pH Scale

26. Structure and Acid-Base Properties
Bond polarity & bond strength affects acidity. In binary compounds:
Bond Polarity (The higher the bond polarity, the stronger the bond, the weaker the acid)
Bond Strength (The lower the bond strength, the higher the resulting H+ ionization and the stronger the acid. )

27. Oxides Acidic Oxides (Acid Anhydrides):
OX bond is strong and covalent.
SO2, NO2, CrO3
Basic Oxides (Basic Anhydrides):
OX bond is ionic.
K2O, CaO

28. Neutralization Reactions

29. Aqueous Reactions: Neutralization Net Ionic Equations
HCl(aq) + NaOH (aq) ---> NaCl (aq) + H2O(l)
___________________________________________________
HCl(aq) ---> H+(aq) + Cl -(aq)
NaOH (aq) ---> Na+(aq)+ OH-(aq)
NaCl (aq) ---> Na+(aq)+ Cl-(aq)
________________________________________________
Na+(aq)+ OH-(aq) + H+(aq) + Cl -(aq) ---> Na+(aq)+ Cl-(aq) + H2O(l)
_______________________________________________________
H+(aq) + OH -(aq) ---> H2O(l)
© Copyright R.J. Rusay

30. Acid-Base Titration

31. Stomach Chemistry

32. Buffers