1. Chapter 15
Acids and Bases

2. Properties of Acids and Bases
Acids – taste sour, turn litmus paper red
Bases – taste bitter, feel slippery, turn litmus paper blue

3. The Arrhenius Model Acids – produce hydrogen ions in aqueous solution
HCl H+ + Cl-
Bases – produce hydroxide ions in aqueous solution
NaOH  Na+ + OH-

4. The Bronsted-Lowry Model
Arrhenius concept is limited because it only allows for one kind of base
Acid – proton (H+) donor
Base – proton (H+)acceptor

5. General reaction for a Bronsted-Lowry acid dissolving in water:
Conjugate acid-base pair – two substance related to each other by the donating and accepting of a single proton

6. Water acts as a base (proton acceptor) to form a hydronium ion H3O+

7. Identify the acid, base, conjugate acid, and conjugate base in the following:
HCO H2O  CO H3O +1

8. You try:
NH4+(aq) + OH-(aq) ↔ NH3(aq) + H2O(l)

9. Which of the following represents a conjugate acid-base pair?
HF, F-
NH4+, NH3
HCl, H2O

10. What is the conjugate base of the following?
HClO4
HNO2
HBr
What is the conjugate acid of the following?
Br-
H2O
HPO42-

11. Acid Strength Reactions of acids with water are reversible
A strong acid is completely ionized or completely dissociated

12. Weak acid – most of the acid molecules remain intact

14. A strong acid contains a relatively weak conjugate base, one that has a low attraction for protons
A weak acid contains a relatively strong conjugate base

15. Common strong acids are:
Sulfuric acid, H2SO4
Hydrochloric acid, HCl
Nitric acid, HNO3
Perchloric acid, HClO4

16. Oxyacids – acidic hydrogen is attached to an oxygen atom

17. Organic acids – those with a carbon atom backbone
Contain the carboxyl group
Usually weak acids (acetic acid)

18. Other acids – acidic proton attached to an atom other than oxygen
Hydrohalic acids: HX
X = halogen atom

20. Water as an Acid and a Base
Amphoteric substance – can behave either as an acid or as a base
Ionization of water:
One water molecule acts as an acid donating protons, one acts as a base accepting protons

21. The product of [H3O+] and [OH] is always constant:
Kw = ion product constant for water
No matter what the solution contains, Kw will always equal 1.0 x 10-14

23. Calculate the [H+] or [OH] and state whether the solution is neutral, acidic, or basic
1.0 x 10-5 M OH-
1.0 x 10-7 M OH-
10.0 M H+

24. Determining the Acidity of a Solution
The pH Scale: 0 – 14
<7 = acidic
7 = neutral
>7 = basic

25. pH = log [H+]

26. Logs & sig. figs – the number of decimal places for a log must be equal to the number of significant figures in the original number

27. What is the pH of the following?
A solution in which [H+] = 1.0 x 10-9
A solution in which [OH-] = 1.0 x 10-6

28. Because the pH scale is a log scale based on 10, the pH changes by 1 for every power of 10 change in the [H+]

30. Log scales similar to the pH scale are used for representing other quantities:
pOH = log [OH]
pH + pOH = 14.00

31. Calculate the pH and pOH for the following:
1.0 x 10-3 M OH-
1.0 M H+

32. It is also possible to find the [H+] or [OH-] from the pH or pOH by undoing the log operation
[H+]= 10-pH
[OH-] = 10-pOH

33. The pH of a human blood sample was measured to be 7. 41
The pH of a human blood sample was measured to be What is the [H+] and [OH-] in this blood

34. Calculating the pH of Strong Acid Solutions
What is the [H+] in 1.0 M HCl?
What is the pH of a solution made by dissolving 6.3 g HNO3 in 550 mL of water?

35. What is the pH of 0.200 M sulfuric acid?
What is the pH of a M NaOH solution?

36. Measuring pH
Indicators exhibit different colors in acidic and basic solutions
In acidic solution will be in HIn form
In basic solution will be in In- form

37. Indicator paper – strip of paper coated with a combination of indicators, turns a specific color at each pH value
pH meter – contains a probe very sensitive to hydrogen ion concentration

39. Titrations and buffers
Neutralization reaction = strong acid + strong base

40. Neutralization Reactions
An acid-base reaction is called a neutralization reaction.
Steps to solve these problems are the same as before.

41. What volume of a 0. 100 M HCl solution is needed to neutralize 25
What volume of a M HCl solution is needed to neutralize 25.0 mL of a M NaOH solution?

42. What volume of 0. 100 M H2SO4 is needed to neutralize 50 mL of 0
What volume of M H2SO4 is needed to neutralize 50 mL of 0.25 M NaOH?

43. Acid-Base Titrations
Titration – delivery of a measured volume of solution of known concentration (the titrant) in to the solution being analyzed (the analyte)
Titrant contains a substance that reacts in a known way with the analyte
If analyte contained a base, the titrant would be a strong acid of known concentration

44. Standard solution is loaded into a buret
Allows an accurate measurement of the delivery of a given volume of liquid

45. Titration is added slowly to analyte until exactly enough has been added to just react with all of the analyte
Stoichiometric point or equivalence point
For strong acid & strong base equivalence point is when pH = 7

46. Titration curve (pH curve) – plot of pH vs volume of titrant added

47. Buffered Solutions
Buffered solution – one that resists a change in its pH even when a strong acid or base are added to it
Presence of a weak acid and its conjugate base buffers a solution