chapter 16 acids and bases ionization of water the ph scale 7-4
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Chapter 16Acids and Bases
Ionization of Water
The pH Scale
7-4
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-]
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+]
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+
a. 1.0 x 10-9 Mb. 1.0 x 10-7 Mc. 1.0 x 10-15 M
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