Acids and Bases

Ionization of Water The pH Scale

Ionization of Water

Occasionally, in water, a H + is transferred between H 2 O 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: H 3 O + and OH H 2 O + H H 3 O + OH 2 O H 3 O + + OH hydroxonium hydroxide ion ion 1 x 10 -7 M 1 x 10 -7 M

Ion Product of Water K

w [ ] = Molar concentration K w = [ H 3 O + ] [ OH ] = [ 1 x 10 -7 ][ 1 x 10 -7 ] = 1 x 10 -14

Acids



Increase H +



HCl (g) + H 2 O (l) H 3 O + (aq) + Cl (aq)



More [H 3 O + ] than water > 1 x 10 -7 M



As H 3 O + increases, OH decreases [H 3 O + ] > [OH ] H 3 O + OH -

Bases



Increase the hydroxide ions (OH )



NaOH (s) H 2 O Na + (aq) + OH (aq)



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



When OH increases, H 3 O + decreases [OH



] > [H 3 O + ] OH H 3 O +

Using K

w The [OH ] of a solution is 1.0 x 10 - 3 M. What is the [H 3 O + ]?

K w = [H 3 O + ] [OH ] = 1.0 x 10 -14 [H 3 O + ] = 1.0 x 10 -14 [OH ] [H 3 O + ] = 1.0 x 10 -14 1.0 x 10 - 3 = 1.0 x 10 -11 M

Learning Check pH1

The [H 3 O + ] of lemon juice is 1.0 x 10 -3 What is the [OH ] of the solution?

M. 1) 1.0 x 10 3 M 2) 3) 1.0 x 10 -11 M 1.0 x 10 11 M

Solution pH1

The [H 3 O + ] of lemon juice is 1.0 x 10 - 3 M. What is the [OH ]?

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

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 [H 3 O + ] of the solution?

1) 2) 3) 2 x 10 - 5 M 1 x 10 10 M 2 x 10 -10 M

Solution pH2

The [OH ] of a water solution is 5 x 10 -5 M. What is the [H 3 O + ] in the solution?

[ H 3 O + ] = 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 [H 3 O + ] 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 [H 3 O + ] 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

K w = [H 3 O + ][OH ] = 1.0 x 10 14 A. (3) [OH ] = 1.0 x 10 -14 = 1.0 x 10 1.0 x 10 - 4 -10 B.

(2) [H 3 O + ] = 1.0 x 10 -14 = 2 x 10 - 6 5 x 10 - 9

pH



Indicates the acidity [H 3 O + ] of the solution



pH = - log [H 3 O + ]



From the French pouvoir hydrogene

(“hydrogen power” or power of hydrogen)

pH

In the expression for [H 3 O + ] 1 x 10 -exponent the exponent = pH

[H

3

O

+

] = 1 x 10

pH

M

pH Range

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Acidic Basic [H + ] > [OH ] Neutral [H + ] = [OH ] [OH ] > [H + ]

Some [H

3

O

+

] and pH

[H 3 O + ]

1 x 10

5

M 1 x 10

9

M 1 x 10

11

M

pH 5 9 11

pH of Some Common Acids gastric juice lemon juice vinegar orange juice coffee milk 1.0

2.3

2.8

3.5

5.0

6.6

pH of Some Common Bases blood tears seawater milk of magnesia household ammonia 7.4

7.4

8.4

10.6

11.0

Learning Check pH4

A. The [H 3 O + ] 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. [H 3 O + ] = 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 [H 3 O + ] of the soap solution?

1) 1 x 10 - 4 M 2) 1 x 10 10 M 3) 1 x 10 - 10 M

Solution pH5

The pH of a soap is 10. What is the [H 3 O + ] of the soap solution?

[H 3 O + ] = 1 x 10 pH M = 1 x 10 10 M

pH on the Calculator

[H 3 O + ] 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 [H 3 O + ] = 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 [H 3 O + ] = 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 A. _____ HCl with a pH = 1.5 3. neutral 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 A. _1__ HCl with a pH = 1.5 B. _2__ 3. neutral Pancreatic fluid [H + ] = 1 x 10 -8 M C. _1__ D. _3__ E. _1__ F. _2__ Sprite soft drink pH = 3.0

pH = 7.0

[OH ] = 3 x 10 -10 M [H + ] = 5 x 10 -12

Acid Rain



Unpolluted rain has a pH of 5.6



Rain with a pH below 5.6 is “acid rain“



CO 2 in the air forms carbonic acid CO 2 + H 2 O



Adds to H + of rain H 2 CO 3 H 2 CO 3 H + (aq) + HCO 3 -(aq)

Sources of Acid Rain



Power stations



Oil refineries



Coal with high S content



Car and truck emissions



Bacterial decomposition, and lighting hitting N 2

SO 2 NO and NO 2 Mt. St Helens (1980) 26 million tons in 1980 22 million tons in 1980 400,000 tons SO 2



Reactions with oxygen in air form SO 3 2SO 2 + O 2 2 SO 3



Reactions with water in air form acids SO 3 + H 2 O NO + H 2 O H 2 SO 4 sulphuric acid HNO 2 nitrous acid HNO 2 + H 2 O HNO 3 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