Chapter 16Acids and Bases

Ionization of Water

The pH Scale

Measuring pH

• Why measure pH?–Everything from swimming pools,

soil conditions for plants, medical diagnosis, soaps and shampoos, etc.

• Sometimes we can use indicators, other times we might need a pH meter

pH of Some Common Acids

gastric juice 1.0

lemon juice 2.3

vinegar 2.8

orange juice 3.5

coffee 5.0

milk 6.6

pH of Some Common Bases

blood 7.4

tears 7.4

seawater 8.4

milk of magnesia 10.6

household ammonia 11.0

Calculating pH, pOHpH = -log10 [H3O+]

pOH = -log10 [OH-]

Relationship between pH and Relationship between pH and pOHpOH pH + pOH = 14

Finding [HFinding [H33OO++], [OH], [OH--] from pH, pOH] from pH, pOH

[H3O+] = 10-pH

[OH-] = 10-pOH

In pure water, [H3O+] = [OH-] = 1 10 –7 Kw = 1 10 –14

pH pOH

[H+] [OH-]

pH + pOH = 14

pOH = -log[OH-]pH = -log[H+]

[H+][OH-] = 1.0 10-14

pH +

pOH = 14

Ionization of Water

Occasionally, in water, a H+ is transferred between H2O molecules

. . . . . . . .H:O: + :O:H H:O:H + + :O:H-

. . . . . . . . H H H

water molecules hydronium hydroxide ion (+) ion (-)

Pure Water is Neutral

Pure water contains small, but equal amounts of ions: H3O+ and OH-

H2O + H2O H3O+ + OH-

hydronium hydroxide

ion ion

1 x 10-7 M 1 x 10-7 MH3O+ OH-

Ion Product of Water Kw

[ ] = Molar concentration

Kw = [ H3O+ ] [ OH- ]

= [ 1 x 10-7 ][ 1 x 10-7 ]

= 1 x 10-14

Acids

Increase H+

HCl (g) + H2O (l) H3O+ (aq) + Cl-

(aq)

More [H3O+] than water > 1 x 10-7M

As H3O+ increases, OH- decreases

[H3O+] > [OH-]H3O+

OH-

Bases

Increase the hydroxide ions (OH-)

H2O

NaOH (s) Na+(aq) + OH- (aq)

More [OH-] than water, [OH-] > 1 x 10-7M

When OH- increases, H3O+ decreases

[OH] > [H3O+]

H3O+OH-

Using Kw

The [OH- ] of a solution is 1.0 x 10- 3 M. What is the

[H3O+]?

Kw = [H3O+ ] [OH- ] = 1.0 x 10-14

[H3O+] = 1.0 x 10-14

[OH-]

[H3O+] = 1.0 x 10-14 = 1.0 x 10-11 M

1.0 x 10- 3

Learning Check pH

The [H3O+] of lemon juice is 3.0 x 10-3 M. What

is the [OH-] of the solution?

Kw = [H3O+ ] [OH- ] = 1.0 x 10-14

[OH- ] = 1.0 x 10-14

[H3O+]

[OH- ] = 1.0 x 10-14 = 3.3 x 10-12 M

3.0 x 10- 3

pH

The [H3O+] of lemon juice is 9.0 x 10- 4 M.

What is the [OH-]?

[OH- ] = 1.0 x 10 -14 = 1.1 x 10-11 M 9.0 x 10 - 4

The [H3O+] is 4.0 x 10- 5 M. What is the [OH-]?

1.0 x 10 -14

4.0 x 10-5

Enter 1.0 EE +/- 14 4.0 EE +/- 5

= 2.5 x 10 -10

Solution pH

B.The [H3O+] when [OH- ] of 5 x 10-9 M

Kw = [H3O+ ][OH-] = 1.0 x 10 14

[H3O+] = 1.0 x 10 -14 = 2 x 10 - 6

5 x 10- 9

pH

Indicates the acidity [H3O+] of the solution

pH = - log [H3O+]

From the French pouvoir hydrogene

(“hydrogen power” or power of

hydrogen)

In the expression for [H3O+]

1 x 10-exponent

the exponent = pH

[H3O+] = 1 x 10-pH M

pH

pH Range

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Neutral

[H+]>[OH-] [H+] = [OH-] [OH-]>[H+]

Acidic Basic

pH

A. The [H3O+] of tomato juice is 1 x 10-4 M. What is the pH of the solution?

answer: 4

pH = - log [ 1 x 10-4] = -(- 4) = 4

pH

B. The [OH-] of an ammonia solution is

1 x 10-3 M. What is the pH of the solution?

Answer: 11

[H3O+] = 1 x 10-11

pH = - log [ 1 x 10- 11] = -(- 11) = 11

Some [H3O+] and pH

[H3O+] pH

1 x 10-5 M 5

1 x 10-9 M 9

1 x 10-11 M 11

Solution pH

The pH of a soap is 10. What is the [H3O+]

of the soap solution?

[H3O+] = 1 x 10-pH M

= 1 x 10-10 M

pH on the Calculator

[H3O+] is 4.5 x 10-6 M. What is the pH.

pH = 4.5 x EXP(or EE) 6+/- LOG +/-

= 5.35

Learning Check pH

A soap solution has a [H3O+] = 2 x 10-8 M.

What is the pH of the solution?

pH

A soap solution has a [H3O+] = 2.0 x 10-8

M. What is the pH of the solution?

2.0 EE 8 +/- LOG +/- = 7.7

Learning Check

Identify each solution as

1. acidic 2. basic 3. neutral

A. _____ HCl with a pH = 1.5

B. _____ Pancreatic fluid [H+] = 1 x 10-8 M

C. _____ Sprite soft drink pH = 3.0

D. _____ pH = 7.0

E. _____ [OH- ] = 3 x 10-10 M

F. _____ [H+ ] = 5 x 10-12

1

2

1

3

1

2

What is the [H3O+ ] or [OH- ] in each of the following solutions, also state if the solution is neutral, acidic, or basic.a. 1 10 -5 M OH- b. 1 10 -7 M OH- c. 10.0 M H+