Topics 9 & 18Acids and Bases

Ionization of Water

The pH Scale

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 hydroxonium hydroxide ion (+) ion (-)

Pure Water is Neutral

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

H2O + H2O H3O+ + OH-

hydroxonium 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 pH1

The [H3O+] of lemon juice is 1.0 x 10-3 M.

What is the [OH-] of the solution?

1) 1.0 x 103 M

2) 1.0 x 10-11 M

3) 1.0 x 1011 M

Solution pH1

The [H3O+] of lemon juice is 1.0 x 10- 3 M.

What is the [OH-]?

[OH- ] = 1.0 x 10 -14 = 1.0 x 10-11 M 1.0 x 10 - 3

Using the Calculator

1.0 x 10 -14

4.0 x 10-5

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

= 2.5 x 10 -10

Learning Check pH2

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

1) 2 x 10- 5 M

2) 1 x 1010 M

3) 2 x 10-10 M

Solution pH2

The [OH-] of a water solution is 5 x 10-5 M.

What is the [H3O+] in the solution?

[ H3O+] = 1.0 x 10 -14

5 x 10- 5

On some calculators:

1.0 EE +/- 14 5 EE +/- 5 = 2 x 10 -10 M

Learning Check pH3

A.The [OH-] when [H3O+ ] of 1 x 10- 4 M

1) 1 x 10-6 M

2) 1 x 10-8 M

3) 1 x 10-10 M

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

1) 1 x 10- 6 M

2) 2 x 10- 6 M

3) 2 x 10-7 M

Solution pH3

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

A. (3) [OH- ] = 1.0 x 10 -14 = 1.0 x 10 -10

1.0 x 10- 4

B. (2) [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

Some [H3O+] and pH

[H3O+] pH

1 x 10-5 M 5

1 x 10-9 M 9

1 x 10-11 M 11

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 ammonia11.0

Learning Check pH4

A. The [H3O+] of tomato juice is 1 x 10-4 M.

What is the pH of the solution?

1) - 4 2) 4 3) 8

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

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

1) 3 2) 11 3) -11

Solution pH4

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

B. [H3O+] = 1 x 10-11

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

Learning Check pH5

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

solution?

1) 1 x 10 - 4 M

2) 1 x 1010 M

3) 1 x 10 - 10 M

Solution pH5

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

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

= 5.35

Learning Check pH6

A soap solution has a [H3O+] = 2 x 10-8 M. What is the pH of

the solution?

1) 8

2) 7.7

3) 6

Solution pH6

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

8 M. What is the pH of the solution?

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

Learning Check pH7

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

Solution pH7

Identify each solution as

1. acidic 2. basic 3. neutral

A. _1__ HCl with a pH = 1.5

B. _2__ Pancreatic fluid [H+] = 1 x 10-8 M

C. _1__ Sprite soft drink pH = 3.0

D. _3__ pH = 7.0

E. _1__ [OH-] = 3 x 10-10 M

F. _2__ [H+] = 5 x 10-12

Acid RainUnpolluted rain has a pH of 5.6

Rain with a pH below 5.6 is “acid rain“

CO2 in the air forms carbonic acid

CO2 + H2O H2CO3

Adds to H+ of rain

H2CO3 H+ (aq) + HCO3-(aq)

Formation of acid rain:

1. Emission of sulfur and nitrogen oxides from the burning of fuels expecially coal with high S content, power stations, oil refineries, vehicles as well as bacterial decomposition, and lighting hitting N2

SO2 26 million tons in 1980

NO and NO2 22 million tons in 1980

Mt. St Helens (1980) 400,000 tons SO2

2. Reactions in the atmosphere form SO3

2SO2 + O2 2 SO3

3. Reactions with atmosphere water form acids

SO3 + H2O H2SO4 sulfuric acid

NO + H2O HNO2 nitrous acid

HNO2 + H2O HNO3 nitric acid

4. Effects of Acid Rain

Decline in fish populations in rivers and lasts due to toxic effect of Al leached from soil by acid rain

Extensive fish kills in spring from runoff due to accumulation of large amounts of acid on the snow

Dissolves minerals Mg, Ca, and K from the soil and waxy coatings that protect leaves from bacteria

Corrodes metals, textiles, paper and leather

Sources of Acid Rain

Power stations

Oil refineries

Coal with high S content

Car and truck emissions

Bacterial decomposition, and lighting

hitting N2

SO2 26 million tons in 1980

NO and NO2 22 million tons in 1980

Mt. St Helens (1980) 400,000 tons SO2

Reactions with oxygen in air form SO3

2SO2 + O2 2 SO3

Reactions with water in air form acids

SO3 + H2O H2SO4 sulphuric acid

NO + H2O HNO2 nitrous acid

HNO2 + H2O HNO3 nitric acid

Effects of Acid Rain

Leaches Al from soil, which kills fish

Fish kills in spring from runoff due to

accumulation of large amounts of acid in

snow

Dissolves waxy coatings that protect leaves

from bacteria

Corrodes metals, textiles, paper and leather