Acids and Bases

1
Chapter 16

• Acids and Bases

2
Characteristics

• Acids
• Bases
• Change the color of dyes

3
Characteristics

• Add acid to water makes water
• Add base to water makes it more
• Add acid to base
• NaOH HCl ? NaCl H2O

4
Arrhenius

• Acids

• Bases

5
Bronsted/Lowry

• Acids

• Bases

6
Water as a Bronsted/Lowry

• H2O ? H OH-
• H H2O ? H3O
• Hydronium can bond to many other water molecules

7
Water and Hydronium

• H2O HCl ? H3O Cl-

8
Ammonia as a base

• HCl NH3 ? NH4 Cl-
• H2O NH3 ? NH4 OH-
• An acid and a base always work together to
  transfer protons.

9
Amphoteric Species

• A compound that can
• Water
• Base with HCl
• Acid with NH3

10
Conjugate acids and bases

• Every acid/base reaction has
• H2O NH3 ? NH4 OH-

11
Practice

• What are the conjugate bases of the following
  acids?

12
Practice

• What are the conjugate acids of the following
  bases?

13
Strong Acids

• 100 ionized
• Reaction is not reversible

14
Strong Bases

• 100 ionized
• CH3- is a VERY strong base
• No acidity and takes proton from water

15
Weak Acids

• Slightly dissociated
• CH3COOH H2O ? CH3COO- H3O
• Scale on page 598, fig 16.4

16
Generally

• HX H2O ? H3O X-
• Equilibrium favors transfer of proton from
  stronger acid to stronger base

17
Practice

• NH4 OH- ? NH3 H2O
• Does the equilibrium lie to the right or left?
• Why

18
Autoionization of water

• H2O H2O ? H3O OH-
• This is a very fast reaction
• Only about 1 out of 109 water molecules are
  dissociated at any time

19
Generally

• Shown as
• H2O ? H OH-

20
Ion Product

• H2O(l) H2O(l) ? H3O(aq) OH-(aq)
• Kc
• But water is a constant so

21
MEMORIZE THIS!

• Kc
• Kw
• At equilibrium

22
Practice

• Remember at equilibrium
• Identify the following as acid or base
• H 1 e 5
• OH- 3.2 e 9
• H 7.1 e 8
• OH- 4.6 e 3

23
pH scale

• Pain to always use exponents
• Use logarithmic scale to deal with exponent
• MEMORIZE

24
So

• If
• Therefore the pH of a neutral solution is 7
• (equal amounts of H and OH-)

25
Calculations involving pH

• If given OH- there are two methods to get pH
• 1.

26
Calculations involving pH

• What is pH if OH- 3.2 e-5?
• 2.

27
The pH scale

• If the pH lt 7, the solution is acidic
• If the pH gt 7, the solution is basic
• If the pH 7, the solution is neutral
• See fig 16.5 p. 602

28
Practice

• Calculate the pH of lemon juice that has a

29
How do you undo a logarithm?

• If
• Then

30
Practice

• What is the H of a solution that has a pH of
• What is the OH- of each solution?

31
Practice

• What is the pH of
• What is the pH of
• What is HNO3 is

32
Quiz

1. What is the pH of a solution that has OH-
2. What is the H of a solution that has a
3. What is the pOH of a solution that has a
4. Identify all of the above as either acid/base

33
Weak Acids

• Write the acid ionization expression for HCHO2,
  formic acid, dissolving in water. This is an
  equilibrium expression.
• This gets the designation

34
HCHO2 ? H CHO2-

• A student prepared a 0.10 M solution of formic
  acid and measured its pH. At 25oC, it was found
  to be 2.38.
• Calculate Ka
• ICE BOX!!!

35
Niacin

• A 0.20 M solution of niacin has a pH of 3.26.
  what is the Ka for niacin?
• ICE BOX!!!!