1. Unit 16: Acids and Bases, and pH
acidic solution
basic solution
Arrhenius model
Brønsted-Lowry model
conjugate acid
conjugate base
conjugate acid-base pair
amphoteric
Lewis model
strong acid
weak acid
acid ionization constant
strong base
weak base
base ionization constant
acid-base indicator
end point
salt hydrolysis
buffer
buffer capacity

2. Acids and Bases: An Introduction
Aqueous Solutions = acid + base
hydrogen ions (H+) + hydroxide ions (OH-)
hydronium ion (H3O+) is a hydrated hydrogen ion.
The acidic symbols (H+) and (H3O+) can be used interchangeably in chemical equations.

3. All aqueous solutions contain hydrogen ions (H+) and hydroxide ions (OH-).
An acidic solution contains more H+ ions than OH- ions, whereas a basic solution contains more OH- ions than H+ ions
A neutral solution contains equal concentrations of H+ ions and OH- ions

4. Macroscopic Properties of Acids and Bases
Taste and feel:
Acids taste sour (lemon juice, vinegar)Bases taste bitterBases are slippery (soap)

5. Acids react with bases – the reaction of acids and bases are central to the chemistry of living systems, the environment, and many important industrial processes

6. Substance Acid/Base Some Uses
Common Industrial Acids and Bases
Substance
Acid/Base
Some Uses
Sulfuric Acid (H2SO4)
Acid
Car batteries; manufacture of chemicals, fertilizer, and paper
Lime (CaO)
Base
Neutralization of acidic soil
Ammonia (NH3)
Fertilizer, cleaner, manufacture of rayon, nylon and nitric acid
Sodium hydroxide (NaOH)
Drain and oven cleaners; manufacture of soap and chemicals
Phosphoric acid (H3PO4)
Soft drinks, manufacture of detergents and fertilizers

7. Litmus test:Indicators-
change colors in the presence of an acid or a base
Litmus:
base = blue
acid = red

8. Submicroscopic Behavior of Acids: Hydronium ion formation
Submicroscopic Behavior of Acids: Hydronium ion formation HCl + H2O H3O+ + Cl- HNO3 + H2O H3O+ + NO3-

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

10. The Bronsted-Lowry Model
Arrhenius concept is limited because it only allows for one kind of base. It expresses the substance.
Acid – proton donor
Base – proton acceptor
The Bronsted-Lowry Model

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

12. Brønsted-Lowry Model HCl + H2O H3O+ + Cl- acid conjugate base
base conjugate acid
HNO3 + H2O H3O+ + NO3-
acid conjugate base

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

14. 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

15. Ionization Example H3BO4(aq) + H2O(l) ↔ H2BO4-(aq) + H3O+(l)
Boric Acid, H3BO4
H3BO4(aq) + H2O(l) ↔ H2BO4-(aq) + H3O+(l)
H2BO4-(aq) + H2O(l) ↔ HBO42-(aq) + H3O+(l)
HBO42-(aq)) + H2O(l) ↔ BO43-(aq) + H3O+(l)

17. Monoprotic and Polyprotic Acids
Hydrogen atoms that are bonded to electronegative elements are ionizable
Monoprotic acid can donate only one hydrogen Example- HCl
Polyprotic acids can donate more than one hydrogen atom
diprotic acid has two ionizable hydrogens Example: sulfuric acid
triprotic acids has three ionizable hydrogens Example: Boric acid

18. Strengths of Acids and Bases
Strong acids and bases ionize completely
Weak acids and bases ionize only partially

20. 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

21. Hydrogen and Hydroxide Ions and pH
Acidity or Basicity of a substance is related to the concentration of hydrogen and hydroxide ions in that substance

22. The product of [H+] 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

24. 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+

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

27. A mathematical scale in which the concentration of H+ ions in a solution is expressed as a number from 0 – 14
pH = −log [H+]

28. What is the pH of solutions having the following ion concentrations?
[H+] = 1.0 x 10-2 M
[H+] = 3.0 x 10-6 M

29. 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−]

31. What is the pOH of a solution having the following ion concentration?
[OH-] = 1.0 x 10-6 M
[OH-] = 6.5 x 10-4 M

32. pH + pOH = 14 What is the pOH of a solution whose pH is 5?
What is the pH of a solution whose [OH-] = 4.0 x 10-3 M

33. Calculate the pH and pOH of the following solutions:
[H+] = M
[OH-] = M

34. 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

35. 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?

36. Neautralization Reactions
Acid + Base salt + water
HCl + NaOHNaCl + H2O
Ionic:
Net ionic:

37. Titration
Method for determining the concentration of a solution by reacting a known volume of that solution with a solution of known concentration.
If unknown is acid, known must be base

38. Titration procedure
Measured volume of acid or base of unknown concentration is placed in a flask and initial pH is recorded
Buret is filled with the solution of known concentration (standard solution/titrant)
Standard solution added slowly until neutral pH is reached (equivalence point)
[H+] = [OH-]

40. End point of a titration can be measured using a pH meter or an indicator
Indicator changes color at different pH values

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

42. A volume of 18. 28 mL of a standard soluiton of 0
A volume of mL of a standard soluiton of M NaOH was required to neutralize mL of a solution of nitric acid. What is the concentration of the nitric acid?

43. Buffered Solutions
Solutions that resist changes in pH when acids or bases are added
Weak acid + conjugate base
HF + NaF