Learning Check …
Did I complete all my homework from last class?
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Are there any homework questions I need help with?
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Water as an Acid or a Base

Pure water dissociates according to the following reaction:

There is an equal amount of _____ and ______ ions in solution (neutral, pH = 7)

at 25°C [H3O+] = [OH-] = ______________________

equilibrium constant for the dissociation of water: _________
Kw
@ 25°C
=
=
=
acids: [H3O+] ___ [OH-]
[H3O+] ____ 1x10-7
[OH-] ____ 1x10-7
bases: [OH-] ____ [H3O+] [H3O+] ____ 1x10-7
[OH-] ____ 1x10-7

We can use Kw to calculate [H3O+] and [OH-] in solutions
RELATIONSHIP BETWEEN Ka and Kb
HA (aq)
A- (aq)
+
+
Ka x Kb =
=
=
H2O (l)
H2O (l)


H3O+ (aq)
+
A- (aq)
HA (aq) + OH- (aq)
Ka =
Kb =
5
•
A ____________- acid or base will produce a __________________ with
_______________ acid/base properties
•
A ____________ acid or base will produce ____________________ that has
___________ acid/base properties
Ex) What is the Kb value for F- if the Ka value of HF is 6.6x10-4?
POLYPROTIC ACIDS
• acids that have more than one proton
• only one proton is transferred at a time
Ex)
H2CO3 +
H2O

pH and pOH
In neutral water,
pH = -log [H3O+] = -(log(1 x 10-7) = 7
pOH = -log [OH-] = -(log(1 x 10-7) = 7
Note: pH + pOH = 14, always, regardless of solution!
Another way to calculate [H3O+] & [OH-] in solution:
Ex)
A liquid shampoo has a [OH-] of 6.8x10-5 mol/L
(a) Is the shampoo acid, basic or neutral?
(b) What is [H3O+]?
(c) What is the pH and pOH of the shampoo?
Self Check
How prepared am I to start my homework? Can I …
… determine [H+] and [OH-] using Kw, pH or pOH
… determine Ka or Kb using Kw
… find pH and pOH of a substance
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