PH Scale and Calculations

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Slide 1

pH Scale and Calculations

Chapter 14

Page 565-574

Slide 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.

Slide 3

pH Scale

Acid

Base

0

7

14

Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 515

Slide 4

pH of Common Substances

Timberlake, Chemistry 7th Edition, page 335

Slide 5

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 M

Household bleach

Household ammonia

Lime water

Milk of magnesia

Borax

Baking soda

Egg white, seawater

Human blood, tears

Milk

Saliva

Rain

Black coffee

Banana

Tomatoes

Wine

Cola, vinegar

Lemon juice

Gastric juice

More basic

More acidic

pH [H1+] [OH1-] pOH

7 1 x 10-7 1 x 10-7 7

Slide 6

Acid – Base Concentrations

pH = 3

pH = 7

pH = 11

OH-

H3O+

OH-

OH-

H3O+

H3O+

[H3O+] = [OH-]

[H3O+] > [OH-]

[H3O+] < [OH-]

acidic

solution

neutral

solution

basic

solution

concentration (moles/L)

10-14

10-7

10-1

Timberlake, Chemistry 7th Edition, page 332

Slide 7

pH

pH = -log [H+]

Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 285

Slide 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 = [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.

Slide 9