Equilibrium ❮ 221
The pOH of a solution can also be calculated. It is defined as pOH = - log[OH-]. The
pH and the pOH are related:
pH+=pOHpKw=°14.00at 25 C
In any of the problems above in which [H+] or [OH-] was calculated, you can now
calculate the pH or pOH of the solution.
You can estimate the pH of a solution by looking at its [H+]. For example, if a solution
has an [H+] = 1 × 10 -^5 , its pH would be 5. This value was determined from the value of
the exponent in the [H+].
Kb—the Base Dissociation Constant
Weak bases (B), when placed into water, also establish an equilibrium system much like weak
acids:
B(aq)++HO 2 (l)H B(+−aq)OH(aq)
pH
14
13
12
11
10
9 8 7 6 5 4 3 2 1 0
1 M NaOH
(14.0)
Household
ammonia (11.9)
Milk of magnesia
(10.5)
Detergent
solution (~10)
Seawater (7.0–8.3)
Blood (7.4)
NEUTRAL
Milk (6.4)
Urine (4.8–7.5)
Rainwater (5.6)
Vinegar
(2.4–3.4)
Lemon juice
(2.2–2.4)
Stomach acid
(1.0–3.0)
1 M HCl (0.0)
MORE BASIC
MORE ACIDIC
Figure 15.2 The pH scale.