5 Steps to a 5 AP Chemistry 2019

(Marvins-Underground-K-12) #1
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.
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