Acids and Bases

1
Chapter 9

• Acids and Bases

2
Autoionization of water

• Equation
• Hydronium ion
• No free H,

3
Autoionization

• Dynamic equilibrium

4
Problem

• Write the equilibrium expression for the
  autoionization of water.
• In pure water at 25oC,

5
Therefore

• Kw
• How much ion is present, relatively speaking? A
  lot or a little?
• If H increases what must happen to OH-?

6
What are Acids/Bases?
Acids
Bases

• Produce H
• Neutralize bases to produce salt water

• Produce OH-
• Neutralize acids to produce salt water

7
Indicators

• Litmus, blue and red
• Universal
• Phenolphthalein
• Red cabbage juice
• Phenol red

8
Strong Acids

• No equilibrium

• HCl
• HI
• HClO4

9
Strong Bases

• No equilibrium

• Ba(OH)2

10
Practice I

• What is the concentration of hydronium ion in a
  0.0400 M solution of HNO3?

11
Practice II

• What is the OH- in a solution of KOH that ha a
  concentration of 0.320 M?

12
Practice III

• What is the H in a 0.400 M solution of H2SO4?

13
Practice IV

• What is the OH- in a solution of HCl that has
  a H 0.00300 M?

14
Practice V

• What is the H in a 0.0500 M Ba(OH)2?

15
pH

• Logarithmic scale
• pH

16
pH

• So if H
• pH
• Pure water

17
pH

• To find H given pH, use
• H

18
pH scale
1
7
14
Acid
Neutral
Base
19
pOH

• Calculated the same way, but using OH-
• pH pOH
• From Kw

20
Weak Acids and Bases

• If the acid/base is not one of the strong, it is
  considered weak
• Majority of acids and bases
• React with water,

21
Practice I

• Write the equilibrium expression for formic acid
  reacting with water
• Keq

22
Practice II

• Repeat the above for NH3 reacting with water
• Keq
• Also called

23
Conjugate Acids and Bases

• Write the reaction between nitrous acid, HNO2 and
  water
• Write the reaction between nitrite ion and water

24
Ka and Kb

• Multiply
• Cancel items that cancel
• What do you get?

25
Practice

• What is Ka for carbonate ion if Kb 2.19 x 10-4

26
pKa and pKb

• Determining Ka from pKa

27
Polyprotic acids

• Write the dissociations for H3PO4, a weak acid.
  There are three steps
• Ka1 5.93 e-3
• Ka2 6.32 e-8
• Ka3 4.84 e-13

28
Salts and Hydrolysis

• Ions of a strong acids or bases
• Ions of weak acids and bases

29
Practice

• Predict whether each of the following will make
  an acidic, basic, or neutral solution.
• Mg(NO)3
• K2CO3
• NH4NO3

30
Buffers

• Resist changes in pH
• Why do companies make buffered aspirin?

31
Buffer system

• Conjugate acid/base pair
• Concentrations of each must be about equal

32
Sponge factor

• One ion acts as a sponge for
• One ion acts as a sponge for
• Greater concentration of acid and base, greater
  the ability to resist pH changes

33
Henderson-Hasselbalch
Base

• pH pKa log
• Tells you what changes in pH will happen with
  addition of acid or base

Acid
34
Practice

• Calculate the pH of a solution that is 0.00600 M
  acetic acid and 0.0080 M sodium acetate.
• What is the pH if the concentration of acetic
  acid is changed to 0.0090 M?

35
Practice

• Determine the buffer system ions to use to have a
  system pH of 6.1 /- 0.3

36
Carbon Dioxide

• CO2(aq) H2O(l) ? H2CO3(aq)
• H2CO3(aq) H2O(l) ? H3O(aq) HCO3-
• pKa
• Used in blood to maintain pH at 7.45
• How?

37
Blood buffer system

• Use Henderson-Hasselbalch
• pH pKa log

HCO3-(aq)
CO2(aq) H2CO3(aq)
38
Blood buffer system

• pKa
• pH-pKa
• So the rest of the equation must equal 1
• Log 10
• Therefore the ratio of HCO3-/(CO2H2CO3)

39
Blood buffer system

• CO2 is constantly being replaced by metabolic
  processes and is present in the blood

40
Blood buffer system

• CO2 is constantly lost
• If CO2 is removed too fast problems arise

41
Smokers

• Inhale CO2
• Look at Henderson-Hasselbalch

42
Respiratory Acidosis

• When CO2 not removed or is added from the
  environment
• pH falls
• Death

43
Equations

• CO2(aq) H2O(l) ? H2CO3(aq)
• H2CO3(aq) H2O(l) ? H3O(aq) HCO3-
• LeChatliers principal

44
Respiratory Alkalosis

• CO2 removed too fast
• Hyperventilation

45
Metabolic Acidosis

• Body attempts to compensate by adding CO2
• Help buffer system by adding HCO3-

46
Metabolic Alkalosis

• Eating too many Rolaids
• Add NH4Cl

47
Titration

• Lab experiment
• React an acid and base to form water
• Measure the endpoint with indicator
• Use MaVa MbVb

48
Practice

• What volume of 0.200 M NaOH is needed to
  completely neutralize 40.00 mL of 0.0855 M HCl?

49
Practice II

• What volume of 0.250 M KOH is needed to
  neutralize 50.0 mL of 0.250 M H2SO4?

50
Practice III

• What is the concentration of HCl if 35.00 mL of
  the acid are neutralized by 61.50 mL of 0.500 M
  NaOH?