Table of Contents
Chapter 19: Acids and Bases
19.3: What is pH?
Acids and Bases: Basic Concepts
Starter
• Define Arrhenius and Brønsted-Lowry
acids and bases
• What is the difference between weak and
strong acids and bases?
• What are some characteristics of acids? bases?
Today, you’ll need a scientific/graphing calculator!
Acids and Bases: Basic Concepts
The ion product constant for water
• Self-ionization of water:
H2O(l)
2H2O(l)
H+(aq) + OH-(aq)
H3O+(aq) + OH-(aq)
Kw =[H+][OH-] = 1.0x10–14
• Just “plug and chug” to solve for concentrations of
either ion
Acids and Bases: Basic Concepts
The ion product constant for water
• When [H+] > [OH-], the solution is acidic
• When [H+] < [OH-], the solution is basic
• When [H+] = [OH-], the solution is neutral
Practice finding [H+] & [OH-]
• The concentration of either the H+ ion or OHion is given. For each solution, calculate [H+]
or [OH-]. State whether the solution is acidic,
basic, or neutral.
[OH-] = 1.0x10-9M, acidic
1. [H+] = 1.0x10-5M
[OH-] = 1.0x10-1M, basic
2. [H+] = 1.0x10-13M
[H+] = 1.0x10-7M, neutral
3. [OH-] = 1.0x10-7M
[H+] = 1.0x10-11M, basic
4. [OH-] = 1.0x10-3M
Acids and Bases: Basic Concepts
Measuring pH
• pH measures acidity.
• Indicators turn different
colors at different pHs.
• pH meters measure the exact
pH of a solution.
Acids and Bases: Basic Concepts
The pH Scale
pH:
• A mathematical scale
• Measures concentration of hydronium
(H3O+) ions in a solution
• Range: 0 to 14
Acids and Bases: Basic Concepts
Interpreting the pH Scale
• pH = 7 is neutral.
• pH < 7 is acidic. lower number = more acidic,
less basic
• pH > 7 is basic. higher number = more
basic, less acidic.
Acids and Bases: Basic Concepts
The pH Scale
[H+]
–11
= 1x10 M
–4
[H3O+]
= 1x10 M
[H3O+]
–4
= 1.1x10 M
pH =11
pH = 4
pH = 3.96
Acids and Bases: Additional Concepts
pH and pOH
• pH scale: show acidity
• pOH scale: shows basicity
Acids and Bases: Additional Concepts
Relationship between pH and pOH
• The pH and pOH values for a solution may
–
+
be determined if either [H ] or [OH ] is
known.
Acids and Bases: Additional Concepts
CALCULATING pH and pOH from [H+]
Ex5) If a carbonated soft drink has a hydrogen ion
–4
concentration of 7.3 x 10 M, what are the pH and
pOH of the soft drink?
Known: [H+]
Calculate pH
Acids and Bases: Additional Concepts
CALCULATING pH and pOH from [H+]
The carbonated soft drink is acidic.
Practice calculating pH
and pOH
• Calculate the pH and pOH of aqueous solutions
having the following ion concentrations.
Ex6) [OH-] = 1.0x10-6M pOH = 6.00, pH = 8.00
Ex7) [OH-] = 6.5x10-4MpOH = 3.19, pH = 10.81
Ex8) [H+] = 3.6x10-9M pH = 8.44, pOH = 5.56
Ex9) [H+-] = 0.025 M pH = 1.60, pOH = 12.40
pH + pOH = 14
pH
pOH
pH=-log[H+]
pOH=-log[OH-]
[H+]
1.0x10-14 = [H+][OH-]
[OH-]
Acids and Bases: Additional Concepts
CALCLUATING ion concentrations from pH
[H+] = 10-pH
[OH ]
=
-pOH
10
Acids and Bases: Additional Concepts
[H+]
–
Calculating
and [OH ] from pH
Ex10) What are [H+] and [OH–] in a solution with a
pH of 9.70?
• Find [H+].
[H+] = 10-pH
= 10-9.70
–10
+
[H ] = 2.0 x 10 M
Acids and Bases: Additional Concepts
[H+]
–
Calculating
and [OH ] from pH
–
+
Ex10) What are [H ] and [OH ] in a solution with a
pH of 9.70?
• Determine pOH
Acids and Bases: Additional Concepts
[H+]
–
Calculating
and [OH ] from pH
–
+
Ex10) What are [H ] and [OH ] in a solution with a
pH of 9.70?
• Find [OH–]
[OH-] = 10-pOH
= 10-4.30
As expected, [OH–] > [H+] in this basic solution.
Practice finding ion
concentrations
• The pH is given for three solutions. Calculate [H+]
and [OH-] in each solution.
+] =4.3x10-3 M
[H
11. pH = 2.37
[OH-]=2.3x10-12 M
12. pH = 11.05 [H+] = 8.9x10-12 M
[OH-]=1.1x10-3 M
13. pH = 6.50 [H+] =3.2x10-7 M
[OH-]=3.2x10-8 M
Acids and Bases: Additional Concepts
CALCLUATING pH of strong acids and bases
• Remember, strong acids and bases completely
break into their ions in water
HCl(aq)→
For every HCl molecule,
[H+] = [HCl]
–
+
H (aq) + Cl (aq)
1 H+ ion is produced.
So,
Mg(OH)2(aq)→ Mg2+(aq) + 2OH–(aq)
For every Mg(OH)2 molecule, 2 OH- ions are
produced. So, [Mg(OH)2] = 2[OH-]
Practice calculating pH of
SA & SB
• Calculate the pH of the following solutions.
1) 1.0 mol/L HI
2) 0.050 mol/L HNO3
3) 1.0 M KOH
4) 2.4x10-5 M Mg(OH)2
pH = 0.00
pH = 1.30
pH = 14.00
pH = 9.68
pH + pOH = 14
pH
pOH
pH=-log[H+]
pOH=-log[OH-]
[H+]=10-pH
[H+]
[OH-]=10-pOH
1.0x10-14 = [H+][OH-]
[OH-]