chapter 19: acids and bases table of contents 19.3: what is ph?
TRANSCRIPT
Chapter 19: Acids and Bases
Table of ContentsTable of Contents
19.3: What is pH?
Starter
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• 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!
The ion product constant for water
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• Self-ionization of water:
Kw =
H2O(l) H+(aq) + OH-
(aq)
• Just “plug and chug” to solve for concentrations of either ion
2H2O(l) H3O+(aq) + OH-
(aq)
[H+][OH-] = 1.0x10–14
The ion product constant for water
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• When [H+] > [OH-], the solution is acidic
• When [H+] < [OH-], the solution is basic
• When [H+] = [OH-], the solution is neutral
Practice finding [H+] & Practice finding [H+] & [OH-][OH-]
• The concentration of either the H+ ion or OH- ion is given. For each solution, calculate [H+] or [OH-]. State whether the solution is acidic, basic, or neutral.1. [H+] = 1.0x10-5M2. [H+] = 1.0x10-13M3. [OH-] = 1.0x10-7M4. [OH-] = 1.0x10-3M
[OH-] = 1.0x10-9M, acidic[OH-] = 1.0x10-1M, basic[H+] = 1.0x10-7M, neutral[H+] = 1.0x10-11M, basic
Measuring pH
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• pH measures acidity.
• pH meters measure the exact pH of a solution.
• Indicators turn different colors at different pHs.
pH:
• A mathematical scale
• Measures concentration of hydronium (H3O+) ions in a solution
• Range: 0 to 14
The pH Scale
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• pH = 7 is neutral. Interpreting the pH Scale
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• pH < 7 is acidic. lower number = more acidic, less basic
• pH > 7 is basic. higher number = more basic, less acidic.
The pH Scale
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[H+] = 1x10–11M
[H3O+] = 1x10–4M
pH =11
pH = 4
[H3O+] = 1.1x10–4M pH = 3.96
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pH and pOH
• pH scale: show acidity
• pOH scale: shows basicity
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Relationship between pH and pOH
• The pH and pOH values for a solution may be determined if either [H+] or [OH–] is known.
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CALCULATING pH and pOH from [H+]
Ex5) If a carbonated soft drink has a hydrogen ion concentration of 7.3 x 10–4M, what are the pH and pOH of the soft drink?
Known: [H+] Calculate pH
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CALCULATING pH and pOH from [H+]
The carbonated soft drink is acidic.
Practice calculating Practice calculating pH and pOHpH and pOH
• Calculate the pH and pOH of aqueous solutions having the following ion concentrations.
Ex6) [OH-] = 1.0x10-6MEx7) [OH-] = 6.5x10-4MEx8) [H+] = 3.6x10-9MEx9) [H+-] = 0.025 M
pOH = 6.00, pH = 8.00pOH = 3.19, pH = 10.81pH = 8.44, pOH = 5.56pH = 1.60, pOH = 12.40
pH pOH
[H+] [OH-]1.0x10-14 = [H+][OH-]
pH + pOH = 14
pH=-log[H+]
pOH=-log[OH-]
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CALCLUATING ion concentrations from pH
[H+] = 10-pH
[OH-] = 10-pOH
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Calculating [H+] and [OH–] from pHEx10) What are [H+] and [OH–] in a solution with a pH of 9.70?
• Find [H+].
[H+] = 2.0 x 10–10 M
[H+] = 10-pH
= 10-9.70
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Calculating [H+] and [OH–] from pH
• Determine pOH
Ex10) What are [H+] and [OH–] in a solution with a pH of 9.70?
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Calculating [H+] and [OH–] from pH
• Find [OH–]
As expected, [OH–] > [H+] in this basic solution.
[OH-] = 10-pOH
= 10-4.30
Ex10) What are [H+] and [OH–] in a solution with a pH of 9.70?
Practice finding ion Practice finding ion concentrationsconcentrations
• The pH is given for three solutions. Calculate [H+] and [OH-] in each solution.
11. pH = 2.37
12. pH = 11.05
13. pH = 6.50
[H+] =4.3x10-3 M[OH-]=2.3x10-12 M
[H+] = 8.9x10-12 M[OH-]=1.1x10-3 M
[H+] =3.2x10-7 M[OH-]=3.2x10-8 M
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CALCLUATING pH of strong acids and bases
Mg(OH)2(aq)→ Mg2+(aq) + 2OH–
(aq)
HCl(aq)→ H+(aq) + Cl–
(aq)
• Remember, strong acids and bases completely break into their ions in water
For every HCl molecule, 1 H+ ion is produced. So, [H+] = [HCl]
For every Mg(OH)2 molecule, 2 OH- ions are produced. So, [Mg(OH)2] = 2[OH-]
Practice calculating Practice calculating pH of SA & SB pH of SA & SB
• Calculate the pH of the following solutions.
1) 1.0 mol/L HI2) 0.050 mol/L HNO3
3) 1.0 M KOH4) 2.4x10-5 M Mg(OH)2
pH = 0.00pH = 1.30pH = 14.00pH = 9.68
pH pOH
[H+] [OH-]1.0x10-14 = [H+][OH-]
pH + pOH = 14
pH=-log[H+]pOH=-log[OH-]
[H+]=10-pH [OH-]=10-pOH