pH 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 logH
• pH can use the concentration of hydronium ions or
  hydrogen ions.

3
pH Scale
7
Acid
Base
0
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 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 M Household bleach Household
ammonia Lime water Milk of magnesia Borax Bakin
g soda Egg white, seawater Human blood,
tears Milk Saliva Rain Black coffee Banana Tomato
es Wine Cola, vinegar Lemon juice Gastric juice
More basic
7 1 x 10-7 1 x 10-7 7
More acidic
6
Acid Base Concentrations
10-1
pH 3
pH 11
OH-
H3O
pH 7
10-7
concentration (moles/L)
OH-
H3O
OH-
H3O
10-14
H3O lt OH-
H3O OH-
H3O gt OH-
acidic solution
neutral solution
basic solution
Timberlake, Chemistry 7th Edition, page 332
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 º H3O OH-
• Kw H3OOH-
• 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
H
10
pH and pOH

• pH - logH3O H3O 10-pH
• pOH - logOH- OH- 10-pOH
• pKw pH pOH 14.00
• neutral solution H3O OH- 10 7 M pH
  7.0
• acidic solution H3O gt 10-7 M pH lt
  7.0
• basic solution H3O lt 10-7 M pH gt 7.0

11
Practice

• Finish the following for homework
• Page 566 12-15 (using Kw)
• Page 569 16-19 (using pH -logH
• Page 572 20-23
• Page 578 2, 6-8