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pH Scale and Calculations
Chapter 14
Page 565-574
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.
pH Scale
Acid Base
0
7
14
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515
pH of Common Substances
Timberlake, Chemistry 7th Edition, page 335
pH of Common Substance
14 1 x 10-14 1 x 10-0 0 13 1 x 10-13 1 x 10-1 1 12 1 x 10-12 1 x 10-2 2 11 1 x 10-11 1 x 10-3 3 10 1 x 10-10 1 x 10-4 4 9 1 x 10-9 1 x 10-5 5 8 1 x 10-8 1 x 10-6 6
6 1 x 10-6 1 x 10-8 8 5 1 x 10-5 1 x 10-9 9 4 1 x 10-4 1 x 10-10 10 3 1 x 10-3 1 x 10-11 11 2 1 x 10-2 1 x 10-12 12 1 1 x 10-1 1 x 10-13 13 0 1 x 100 1 x 10-14 14
NaOH, 0.1 MHousehold bleachHousehold ammonia
Lime waterMilk of magnesia
Borax
Baking sodaEgg white, seawaterHuman blood, tearsMilkSalivaRain
Black coffeeBananaTomatoesWineCola, vinegarLemon juice
Gastric juice
Mor
e ba
sic
Mor
e ac
idic
pH [H1+] [OH1-] pOH
7 1 x 10-7 1 x 10-7 7
Acid – Base Concentrations
pH = 3
pH = 7
pH = 11
OH-
H3O+OH-
OH-H3O+
H3O+
[H3O+] = [OH-] [H3O+] > [OH-] [H3O+] < [OH-]
acidicsolution
neutralsolution
basicsolution
co
nc
en
trat
ion
(m
ole
s/L
)
10-14
10-7
10-1
Timberlake, Chemistry 7th Edition, page 332
pH
pH = -log [H+]
Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 285
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.
OH
H
OH
HO
Self ionization reaction of water:
+O
HH
H
OHOHOH2 32
C)25(at10][OH]O[HK -143w
[OH-]
Kw]O[H3
H
+
+-
pH and pOH
• pH = - log[H3O+] [H3O+] = 10-pH
pOH = - log[OH-] [OH-] = 10-pOH
• pKw = pH + pOH = 14.00
• neutral solution: [H3O+] = [OH-] = 10 –7 M pH = 7.0
acidic solution: [H3O+] > 10-7 M pH < 7.0
basic solution: [H3O+] < 10-7 M pH > 7.0
Practice
• Finish the following for homework
Page 566 #12-15 (using Kw)
Page 569 # 16-19 (using pH = -log[H+]
Page 572 # 20-23
Page 578 # 2, 6-8