P H Scale And Calculations

pH is a measure of the acidity or basicity of a solution. It is defined as the cologarithm of the activity of dissolved hydrogen ions (H+). Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations. The pH scale is not an absolute scale; it is relative to a set of standard solutions whose pH is established by international agreement.

1. pH Scale and Calculations

Chapter 14
Page 565-574

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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.

3. dof Chemisty 2002, page 515

4. vinegar
28 9 soil
55
gastic | carbonated
juice | beverage bread
3.0 a
orange potato
3.5 5.8
|
apple juice urine
| 38 6.0
| | tomato milk
|| 42 64
| | | coffee

5.0

Timberlake, Chomisty 7 Edtion, page 395

water (pure)
7.0

drinking water
7.2

blood
74

detergents
8.0-9.0
bile
8.0

seawater
| 85

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©

pH of Common Substances

1.0M
> NaOH

milk of ye)
magnesia ”
10.5

ammonia

11.0

bleach
| 120

5. ES
>

SR pr
pH of Common Substance
pH [H+] [OH] pOH
14 1x10% 1x109 0
NaOH, 04 M 13 1x1073 1x101 1
> er | 12) 1x10 IDE 2
Fy ve weir 111x107" 1x10% 3
Ai Maem see À
- ae 9 1x10® 1x105 5
ne 8 1x108 1x105 6
Humans, as o 1071x107
> “cr. 6 209 alos E
SB) stack cates 5 1x105 1x109 9
©) Tomatoes 4 1x104 1x107? 10
S| Cola, vineger 3 10108 1010" il
> ee 2 1x102 1x10% 12
Cesticluice 1 or MON 12
0 1x100 11014 14

ay ur,
X Le,

6. 10"
pH =11

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OH: H,0+
'H¿0*] > [on] [H¿0*] = [OH [H,0*] <[OH]

acidic navies!
A ‚sayur,
solution x %

basic
solution

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ter, Car, Scot, Chemisty A Wedd of Choices. 1999, page 285

8. ge
. . “RY
Self-lonization 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 H30* and OH.
H,O + H,O © H,0* + OH:
Ky = [HgO*][OH]

« K, - ion product of water
Ky = 1.0 x 10:14 at 25 °C

« This equilibrium constant is very important because
it applies to all aqueous solutions - acids, bases,
salts, and non-electrolytes - not just to pure water.

ayuno,
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a+
y s

9. a F
Self ionization reaction of wi “sn ¥*

30

O: So,
H" \ ia IS
H H

2H,0 > H,O° + OH
K,, = [H,O'][OH ] = 10% (at25°C)

10. a>
Ez
pH ana po!

+ pH=-log[H¿O] — [H,O*] = 10%!
pOH = - log[OH ] [OH] = 10-PCH

¿>

+ pKy = pH + pOH = 14.00

* neutral solution: [H¿O*] = [OH] =10-7M pH=7.0
acidic solution: [H30*] > 107 M pH < 7.0
basic solution: [H3O*] < 107 M pH > 7.0

11. Practice

« Finish the following for homework

Page 566 #12-15 (using Kw)

Page 569 # 16-19 (using pH = -log[H+]
Page 572 # 20-23

Page 578 # 2, 6-8