1. Chapter 14
Acids and Bases

2. Homework Assigned Questions and Problems (odd only)
Section 14.1 (14.1 to 14.5)
Section 14.2 (14.7 to 14.15)
Section 14.3 (14.17 to 14.25)
Section 14.4
Section 14.5 (14.31 to 14.39)
Section 14.6 (14.41 to 14.49)
Section 14.7 (14.51 to 14.55)
Section 14.8 (14.57 to 14.63)
Additional Questions and Problems and Challenge Questions (except 14.99, )

3. Acids Among the most common and important compounds
Aqueous solutions are important in biological systems and in chemical industrial processes
Characteristics
Cause sour taste of lemons and vinegar
Digest food in stomach
Dissolves some metals generating hydrogen gas
Chemical produced in the largest quantity in the USA
Sulfuric acid H2SO4

4. Acids Acids When dissolved in water will generate H+ and an anion
The H+ that is generated will give a sour taste
Vinegar (acetic acid)
Lemon (citric acid)
Most acids are oxo acids (will also gen. H+)

5. Naming Binary Acids
Use the prefix hydro- before the root name of the element
Add the suffix -ic and the word acid to the root name for the element
Example: HCl
hydrochloric acid
Example: HI
hydroiodic acid
Hydrogen chloride as a gas
Hydrogen iodide as a gas

6. Naming Oxo Acids
Produce H+ and a polyatomic ion when dissolved in water
Composed of hydrogen, oxygen, and another nonmetal
Use the root name of the polyatomic ion
If it ends in -ate use the suffix -ic acid
If it ends in -ite use the suffix -ous acid
Example: H2SO4 (from SO42- , sulfate ion)
sulfuric acid
Example: H2SO3 (from SO32- , sulfite ion)
sulfurous acid
It looks like a hydrogen compound of a polyatomic ion

7. Bases Bases When dissolved in water will generate OH- and a metal ion.
Sometimes called alkalis
The OH- that is generated will give a bitter taste
Slippery feel (like soap)
Most bases that are generated are composed from group 1A and 2A metals
Others such as aluminum and iron III hydroxide are insoluble

8. Naming Bases Most bases are usually ionic compounds
The hydroxide ion has a charge of (-1) and is combined with a positively charged ion (group IA or IIA metal ion)
Hydroxides (bases) are named by their cation first, then the word “hydroxide” is added to the metal cation
Most common bases:
NaOH (sodium hydroxide)
KOH (potassium hydroxide)
Ca(OH)2 (calcium hydroxide)
NH4OH (ammonium hydroxide)

9. Arrhenius
First person to recognize the essential nature of acids and bases
Acids:
Produce hydrogen ions (H+) in water
Bases
Produce hydroxide ions (OH-) in water

10. Brønsted-Lowry Acids and Bases
Limitations to Arrhenius model
Only for aqueous solutions
Free H+ does not exist in water
New model by Brønsted and Lowry
Acid
Any substance that can donate a proton (H+) to another substance: Proton donor
Base
Any substance that can accept a proton from another substance: Proton acceptor

11. Water as a Base
H+ does not exist in water due to the strong attraction to the polar water molecule
H3O+ is called a hydronium ion
Real way that protons exist in water
It is covalently bonded to the water molecule

12. Brønsted-Lowry Model The reaction involves a proton transfer
Acid
Base
Conjugate Acid
Conjugate Base
The reaction involves a proton transfer
Acid can lose its proton to form a conjugate base (something that could accept a proton back again)
Base accepts a proton to form a conjugate acid (something that could donate a proton)

13. Brønsted-Lowry Model
Acid
Base
Conjugate Acid
Conjugate Base
The HCl is the Brønsted-Lowry acid because it is donating proton (H+) to water molecule
The water molecule is the Brønsted-Lowry base since it accepts a proton

14. Conjugate Acid/Base Pairs
Related to each other by donating/accepting a single proton (H+)
The acid of the pair has the proton
The base of the pair does not
Every acid has a conjugate base
Every base has a conjugate acid
“Conjugate” is given to the part of the pair that is produced in the reaction

15. Conjugate Acid/Base Pairs
Each acid is related to a base on the opposite side
If on the reactants side (left side) substances are called “acid” or “base”
If on the products side (right side) substances are called “conjugate acid” or “conjugate base”
Base
Acid
Conjugate Acid
Conjugate Base
Each acid is related to a base on the opposite side

16. Conjugate Acid/Base Pairs
Which of the following represent conjugate acid-base pairs?
H2O, H3O+
OH-, HNO3
H2SO4, SO42-
HC2H3O2, C2H3O2-

17. Conjugate Acid/Base Pairs
H2O, H3O+
OH-, HNO3
H2SO4, SO42-
HC2H3O2, C2H3O2-

18. Strength of Acids
When an acid dissolves in water, it gives its proton to water to form the conjugate base of the acid and a hydronium ion (H3O+)
The strength of the acid is determined by the amount of H3O+ that is produced

19. Strength of Acids Strong acids completely dissociate and form H3O+
If a weak acid, there is nothing stopping the conjugate base and the hydronium ion from reacting to re-form the acid and water
Forward
Reverse

20. Strength of Acids
There is a competition for the proton between the conjugate base and water
Water wins: Acid dissociates completely. It is a strong acid
Conjugate base wins: Acid doesn’t dissociate a lot. It is a weak acid

21. Strong Acids Dissociate 100% (almost)
Have very weak conjugate bases (weak reverse reaction)
Conjugate base does not react readily with H3O+
Forward reaction predominates

22. Weak Acids Don’t dissociate very much Have stronger conjugate bases
Conjugate base does react readily with H3O+
Reverse reaction predominates

23. Types of Acids Multiprotic Acids Can donate more than one proton H2SO4
H3PO4
Strong Acid
Weak Acid

24. Types of Acids Oxo Acids Acid hydrogen is attached to an oxygen
Acids of Polyatomic Ions

25. Types of Acids Organic Acids
Acids with a carbon backbone (carboxyl group)
Acetic Acid (CH3COOH or HC2H3O2)

26. Ionization of Water Water can act as an acid or a base
Amphoteric substance
Base
Acid
Conj Acid
Conj Base

27. Ionization of Water
In sample of pure water a small percentage has dissociated to produce ions
It involves a proton transfer
Results in an equal amount of H+ and OH-
Base
Acid
Conj Acid
Conj Base

28. Ionization of Water Autoionization
Ionizing of water to form hydronium and hydroxide ions at 25 ºC
Doesn’t occur to a large extent
Square brackets around a compound mean “concentration of”

29. Ion-Product Constant for Water
At any temperature, the product of the concentration of H+ and OH- is always a constant
Valid in pure water or water with solutes
Kw (Ion-Product Constant of Water)
Conc. of ion expressed in moles/liter
Is 1x10-14

30. Ion-Product Constant for Water
If the [H+] is increased by the addition of acidic solute, the [OH-] must decrease until the expression is 1.0 × again
Or, if the OH- ions are added to the water, the H+ must likewise decrease

31. Ion-Product Constant for Water
An acid is a substance that will increase the H+ ions in solution
All acidic solutions have a higher [H+] than [OH-]
An base is a substance that will increase the OH- ions in solution
All basic solutions have a higher [OH-] than [H+]

32. Ion-Product Constant for Water
Neutral Solution
Acidic Solution
Basic Solution
In all cases:

33. Example
Calculate [H+] in a solution in which [OH-] = 2.0x10-2 M. Is this solution acidic, basic or neutral?

34. The pH Scale
H+ concentrations range from very high values to extremely small valves
Difficult and inconvenient to work with numbers over such a large range
i.e. [H+] of 10 M is 1000 trillion times greater than 10-14
The pH scale of a solution was proposed as an easier and more practical way to handle such large numbers

35. p Scale
Used to express very small numbers
Based on log 10
If N is a number then pN is:
Take the log of the number and then multiply by (-1) to change the sign

36. The pH Scale
The pH scale is defined as the negative log of the molar hydrogen ion concentration
Logarithms are exponents
The negative powers of 10 in the concentrations are converted to positive numbers

37. Calculating the pH of Solutions
The negative log of the H+ concentration
To determine the number of significant Figures for logs: The number of decimal places for the log is equal to the number of sig. figs. in the concentration (original number)

38. pH Examples Calculate the pH for each of the following solutions
A solution in which [H+]=1.0x10-3 M
A solution in which [OH-]=5.0x10-5 M

39. pH Examples

40. pH Scale pH is a log scale
A change in one unit on the pH scale means a tenfold increase or decrease in [H+]
Every time exponent changes by one, the pH changes by one
lowering the pH increases the [H+]
Small pH = acidic solution
Large pH = basic solution

41. Measuring pH Use a pH meter Use pH paper
Electronic device that measures the pH of the solution
Use pH paper
Paper has a chemical in it that changes to different colors depending on the pH of the solution

42. pOH Scale Same as pH scale, but associated with the [OH-]
Low [OH-] means high pOH
High [OH-] means low pOH

43. pH and pOH
In an aqueous solution, the sum of the pH and pOH is always 14
The value 14 corresponds to the negative log of Kw

44. pH and pOH
[H+] > [OH-]
[H+] = [OH-]
[H+] < [OH-]

45. Example 1
A sample of rain in an area with severe air pollution has a pH of What is the pOH of this rain water?

46. Example 2
The pH of rainwater in a polluted area was found to be What is the [H+] for this rainwater?

47. Example 3
The pOH of a liquid drain cleaner was found to be What is the [OH-] for this cleaner?

48. Calculating pH for Strong Acids
Strong acids dissociate 100%
Solution contains only H+ and the anion of the acid
Find the concentration of H+
Find the pH

49. pH of Strong Acids Calculate the pH of a solution of 5.0x10-3 M HCl
complete
dissociation

50. Reactions of Acids and Bases
Neutralization: The reaction between an acid and a base to form a salt and water
H+ from the acid combines with the OH- from the base to form water
The properties of the both reactants are neutralized
The salt contains the positive ion from the base and the negative ion from the acid

51. Reactions of Acids and Bases
The reaction hydrochloric acid and sodium hydroxide:
A double replacement reaction
Ionic Equation
Net Ionic Equation
acid
base
salt
water

52. Reactions of Acids and Bases
Balancing Neutralization Reactions
Write the reactants and products if HCl reacts with Ba(OH)2
Balance the H+ and OH- in the acid and base

53. Reactions of Acids and Bases
Balance the H2O with the H+ and the OH-
Write the salt from the remaining acid and base

54. Acid-Base Titration
Determining the acid or base concentration in a solution is a routing laboratory practice
The pH only determines the amount of dissociated H+ in solution
Titration will give info about the total number of acid or base molecules present

55. Acid-Base Titration
Add one solution to another until the solute in the first solution has reacted completely with the solute in the second solution
To determine the concentration of an acid solution add a solution of base of known concentration to the flask by a buret

56. Acid-Base Titration molesacid = molesbase
Base addition continues until all the acid has completely reacted with the added base: endpoint
To determine endpoint, an indicator is used to detect when the acid-base reaction is complete
If you know
original volume of the acid
the volume and concentration of the base
the concentration of the acid can be calculated
molesacid = molesbase

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