1) The pH scale is used to measure the strength of acids and bases, with pH defined as the negative log of the hydronium (H3O+) ion concentration.
2) Common substances span the pH scale from 0 to 14, with examples like stomach acid at pH 1 and bleach/drain cleaners at pH 12-13.
3) The pH of a solution depends on the relative concentrations of H3O+ and OH- ions, with acidic solutions having higher H3O+ and basic solutions having higher OH- concentrations.
4) Water self-ionizes according to the equilibrium H2O + H2O
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P H Scale And Calculations
1. pH Scale and Calculations
Chapter 14
Page 565-574
2. pH Scale
• We use this scale to measure the strength
of an acid or base.
• pH is defined as the –log[H+]
• pH can use the concentration of
hydronium ions or hydrogen ions.
3. 7
Acid Base
0 pH Scale 14
Zumdahl, Zumdahl , DeCoste, World of Chemistry 2002, page 515
4. pH of Common Substances
Timberlake, Chemistry 7th Edition, page 335
5. pH of Common Substance
pH [H1+] [OH1-] pOH
14 1 x 10-14 1 x 10-0 0
NaOH, 0.1 M 13 1 x 10-13 1 x 10-1 1
Household bleach
12 1 x 10-12 1 x 10-2 2
More basic
Household ammonia
Lime water 11 1 x 10-11 1 x 10-3 3
Milk of magnesia
10 1 x 10-10 1 x 10-4 4
Borax
9 1 x 10-9 1 x 10-5 5
Baking soda
Egg white, seawater 8 1 x 10-8 1 x 10-6 6
Human blood, tears
Milk 7 1 x 10-7 1 x 10-7 7
Saliva
Rain 6 1 x 10-6 1 x 10-8 8
More acidic
Black coffee 5 1 x 10-5 1 x 10-9 9
Banana
Tomatoes 4 1 x 10-4 1 x 10-10 10
Wine
Cola, vinegar 3 1 x 10-3 1 x 10-11 11
Lemon juice
2 1 x 10-2 1 x 10-12 12
Gastric juice
1 1 x 10-1 1 x 10-13 13
0 1 x 100 1 x 10-14 14
7. pH
pH = -log [H+]
Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 285
8. Self-Ionization Of Water
• Even the purest of water conducts electricity. This
is due to the fact that water self-ionizes, that is, it
creates a small amount of H3O+ and OH-.
H2O + H2O H3O+ + OH-
Kw = [H3O+][OH-]
• Kw - ion product of water
Kw = 1.0 x 10-14 at 25 oC
• This equilibrium constant is very important because
it applies to all aqueous solutions - acids, bases,
salts, and non-electrolytes - not just to pure water.
9. Self ionization reaction of water:
+ -
O O O
H + H H H + O
H H
H H
2 H2O H3 O OH
K w [H3O ] [OH ] 10 -14
(at 25
C)
Kw
[H 3O ]
[OH-]