1. Chapter 19
Acids and Bases

2. 19.1 Properties of acids and Bases
Tastes sour
Burns
Reacts w/metal to make H2
Electrolyte
Formula usually starts with “H”
Indicators
Litmus: blue to red
Phenolphthalein: red to clear
Bases
Tastes bitter
Slippery
Does not react with metals
Electrolyte
Formula usually ends with “OH”
Indicators
Litmus: red to blue
Phenolphthalein: clear to red

3. H2O(l) qe H+(aq) + OH-(aq)
19.1 Acidic or Basic
Ionization of Water
H2O(l) qe H+(aq) + OH-(aq)
Normally, [H+] = [OH-]
Acidic solution : [H+] is greater than [OH-]
Basic solution : [OH-] is greater than [H+] H+
OH- H+
OH- H+
OH-

4. 19.1 Arrhenius Model (1887)
Acid - compound that ionizes to make H+ (proton).
monoprotic acid - 1 ionizable hydrogen (a proton), HCl.
diprotic acid - 2 protons, H2SO4.
triprotic acid - 3 protons, H3PO4.
Base - compound that ionizes to make OH-.

5. Arrhenius definition is easy to use, but is too limited.
Some things act like acids and bases without H+ or OH-.

6. 19.1 Bronsted- Lowery Model (1923)
Acid - proton or hydrogen-ion donor.
HX + H2O qe H3O+ + X-
Base - proton or hydrogen-ion acceptor.
Acid
Base

7. 19.1 Bronsted- Lowery Model (1923)
NH H2O qe NH OH-
In the forward reaction, a hydrogen-ion or proton, leaves water and combines with NH3 to make NH4+. H2O is the proton donor, acid, and NH3 is the proton acceptor, base.
Base
Acid

8. 19.1 Bronsted- Lowery Model (1923)
NH H2O qe NH OH-
In the reverse reaction, NH4+ donates (acid) the proton to OH-(base). Because they are formed from NH3 and H2O, they are called conjugates (differ by a proton).
Conjugate
Acid
Conjugate
Base
Base
Acid

9. 19.1 Bronsted- Lowery Model (1923)
Conjugate acid-base pair – two substances that differ from each other by a proton.
NH H2O qe NH OH-
Conjugate
Acid
Conjugate
Base
Base
Acid

10. 19.1 Bronsted- Lowery Model (1923)
Amphoteric - a substance that can act as both an acid or a base.
HCO H2O qe H2CO OH-
HCl + H2O qe H3O+ + Cl-

11. 19.2 Strong Verses Weak Acids and Bases
Strong Acid/Base
Acids and bases that ionize completely
This means that they are converted into 100% products and are represented in the reaction as a single arrow pointing to the products.

12. 19.2 Strong Verses Weak Acids and Bases
Strong Acid
HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)
Strong Base
NaOH(s)  Na+(aq) + OH-(aq)

13. 19.2 Strong Verses Weak Acids and Bases
Weak acids and bases only partially ionize and are therefore equilibrium reactions.
Weak Acid
HC2H3O2(aq) + H2O(l) qe H3O+(aq) + C2H3O2-(aq)
Weak Base
CH3NH2(aq) + H2O(l) qe CH3NH3+(aq) + OH-(aq)

14. 19.2 Strong Verses Weak Acids and Bases
Because they are equilibrium reactions, we can determine the Keq
HCl(aq) + H2O(l) qe H3O+(aq) + Cl-(aq)
Ka should be small for a weak acid
The larger the Ka the stronger the acid

15. 19.2 Strong Verses Weak Acids and Bases
The same applies for weak bases
Keq = Kb
Kb is small for a weak base
The larger the Kb the stronger the base

16. Concentrated/dilute vs. Strong/weak
Concentrated Weak Acid
Dilute Strong Acid
Concentrated Strong Acid
Dilute Weak Acid

17. H2O(l)  H+(aq) + OH-(aq)
19.3 What is pH?
Remember:
H2O(l)  H+(aq) + OH-(aq)
Normally, [H+] = [OH-]
Acidic solution : [H+] > [OH-]
Basic solution : [OH-] > [H+]

18. H2O(l)  H+(aq) + OH-(aq)
19.3 What is pH?
H2O(l)  H+(aq) + OH-(aq)

19. At 298 K for pure water [H+] and [OH-] both equal 110-7 M.
19.3 What is pH?
At 298 K for pure water [H+] and [OH-] both equal 110-7 M.
[H+][OH-] = 110-14

20. 19.3 What is pH? What is the [OH-] if the [H+]=2.310-4?
[H+][OH-] = 110-14
2.310-4 [OH-] = 110-14
[OH-] = 4.310-11 M

21. 19.3 What is pH?
Because [H+] and [OH-] are such small numbers, scientists invented pH to simplify these odd numbers!
pH = 7 neutral
pH < 7 acidic
pH > 7 basic

22. 19.3 What is pH? Where does pH come from? pH = -log[H+]
p (in pH) means the negative log of the H+ concentration
What is the pH if [H+]=2.310-4?
pH = 3.6
pH = -log[H+]
pOH = -log[OH-]

23. 19.3 What is pH?
How do you find the original concentration from pH and pOH?
Just do the opposite!
To go to pH we used the -log[H+]
[H+] = antilog(-pH)
[OH-] = antilog(-pOH)

24. 19.3 What is pH? How are pH and pOH related? pH + pOH = 14

25. Finding pH from solution concentrations
Strong acids
Monoprotic acids fully ionize
HCl  H+ + Cl-
[H+] = solution concentration
0.002 M HCl  [H+] = M
Strong bases
All strong bases fully ionize
NaOH  Na+ + OH-
Ca(OH)2  Ca2+ + 2OH-
[OH-] = (solution concentration)(# hydroxide ions)
0.002 M NaOH  [OH-] = M
0.002 M Ca(OH)2  M

26. Types of Acid-Base Reactions
The reaction of an acid and a base is called a neutralization reaction.
Hydrochloric acid, HCl, is a common household and laboratory acid.
Sodium hydroxide, NaOH, is a common strong base found in drain cleaning

27. Neutralization Reactions
A solution of hydrochloric acid, HCl, is added to exactly the amount of a solution of basic sodium hydroxide, NaOH, that will react with it.
Click box to view movie clip.

28. Neutralization Reactions
Litmus papers show that the resulting salt solution is neither acidic nor basic.

29. Strong Acid + Strong Base
A typical type of acid-base reaction is one in which both the acid and base are strong.

30. Strong Acid + Strong Base
Instead of an overall equation, an ionic equation, in which substances that primarily exist as ions in solution are shown as ions, can be written.

31. Spectator Ions and the Net Ionic Reaction
When ions common to both sides of the equation are removed from the equation, the result is called the net ionic equation for the reaction of HCl with NaOH.

32. Acid-Base Titrations
The general process of determining the molarity of an acid or a base through the use of an acid-base reaction is called an acid-base titration.
The known reactant molarity is used to find the unknown molarity of the other solution.
Solutions of known molarity that are used in this fashion are called standard solutions.
In a titration, the molarity of one of the reactants, acid or base, is known, but the other is unknown.

33. Acid-Base Titrations
You know that NaOH and HCl react completely.
You know the concentration of the NaOH solution, so it is your standard solution.

34. Acid-Base Titrations
You can use the reaction, the volumes of acid and base used, plus the molarity of the base to determine the molarity of the unlabeled HCl.

35. Acid-Base Titrations

36. Titration moles H+ = moles OH- At neutralization,
How do you find moles?

37. At neutralization (equivalence point),
Titration
At neutralization (equivalence point),
moles H+ = moles OH-
MaVa = MbVb

38. Titration
What is the molarity of a HCl solution if it takes 68 mL of 1.2 M NaOH to neutralize 25 mL of HCl?
HCl + NaOH  NaCl + HOH
If [NaOH] = 1.2 M, what does [OH-] =
MaVa = MbVb
X(25 mL)=(1.2 M)(68 mL)
X = 3.3 M
1.2 M