Autoionization
A basic concept need for many electrolyte
calculations
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Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
The equilibrium constant for this is given a special symbol:
Kw
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
The equilibrium constant for this is given a special symbol
and its value is:
Kw = 1.0000 × 10-14 at 24 EC
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
The value of Kw varies somewhat with temperature:
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
The value of Kw varies somewhat with temperature:
Temperature /EC
0
5
10
15
20
24
25
30
log10 (Kw )
14.9435
14.7338
14.5346
14.3463
14.1669
14.0000
13.9965
13.8330
Kw
1.139 × 10–15
1.846 × 10–15
2.920 × 10–15
4.505 × 10–15
6.809 × 10–15
1.000 × 10–14
1.008 × 10–15
1.469 × 10–15
* data from CRC
handbook, 40th
edition.
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
The equilibrium expression for this reaction is:
Kw = [H3O+][OH–]
notice that XH O . 1
2
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
Kw = [H3O+][OH–]
notice that XH O . 1
2
Example: The OH– ion concentration is 5.0 × 10–4 (at 24EC).
What is the H 3O+ concentration?
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
Kw = [H3O+][OH–]
notice that XH O . 1
2
Example: The OH– ion concentration is 5.0 × 10–4 (at 24EC).
What is the H 3O+ concentration?
Substituting into the equation: 1.0 × 10–14 = [H3O+](5.0 × 10–4)
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
Kw = [H3O+][OH–]
notice that XH O . 1
2
Example: The OH– ion concentration is 5.0 × 10–4 (at 24EC).
What is the H 3O+ concentration?
Substituting into the equation: 1.0 × 10–14 = [H3O+](5.0 × 10–4)
Solving: [H3O+] = 2.0 × 10–11
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
Kw = [H3O+][OH–]
notice that XH O . 1
2
Another example: The OH– and H3O+ ion concentrations are
equal. What are their concentrations at 24EC?
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
Kw = [H3O+][OH–]
notice that XH O . 1
2
Another example: The OH– and H3O+ ion concentrations are
equal. What are their concentrations at 24EC?
Let x = [OH–] = [H3O+] substitute : 1.0 × 10–14 = x2
Autoionization
Autoionization is an important property of electrolytic
solvents. Since in General Chemistry water is mostly
dealt with, this reaction is the spontaneous production of
hydronium ions (H3O+) and hydroxide ions (OH–).
The autoionization reaction of water is:
2H2O º H3O+ + OH–
Kw = [H3O+][OH–]
notice that XH O . 1
2
Another example: The OH– and H3O+ ion concentrations are
equal. What are their concentrations at 24EC?
Let x = [OH–] = [H3O+] substitute : 1.0 × 10–14 = x2
Solving: [H3O+] = [OH–] = 1.0 × 10–7
Autoionization
A basic concept need for many electrolyte
calculations
THE END