pH Practice
How is pH related to the acid or base concentration of a solution?
Ionization of water:
 Water molecules can collide and transfer a hydrogen between them creating a hydronium ion
and a hydroxide ion, this is called the autoionization of water
o H2O(l) + H2O(l)  H3O+(aq) + OH-(aq)
o H+ ions do not exist alone, they bond to H2O molecules to form H3O+
 Autoionization only occurs to a small extent
o In pure water at 25C, [H+] = [OH-] = 1.00 x 10-7 M leading to what is called the ionproduct constant for water, Kw = [H+][OH-] = 1.00 x 10-14 M
pH scale
 The pH scale is a range of numbers, typically from 0 to 14, which represents the [H+] of the
solution.
 pH = -log [H+]
Acids and bases
 Depending on the information that is available, you can define a substance as being acidic,
neutral, or basic as follows:
Acidic solution
Neutral solution
Basic (Alkaline) solution
[H+] > [OH-]
[H+] = [OH-]
[H+] < [OH-]
[H+] > 1.00 x 10-7 M
[H+] = 1.00 x 10-7 M
[H+] < 1.00 x 10-7 M
pH < 7.00
pH = 7.00
pH > 7.00
pH, pOH, [H+], and [OH-] calculations
The following visual can help you keep track of the relationships between various acid/base units:
[H+]
pH = -log[H+]
pH
[H+] = 10-pH
[H+][OH-] = 1.00x10-14 M
[OH-]
Practice
pH + pOH = 14
pOH = -log[OH-]
pOH
[OH-] = 10-pOH
1. Root beer has a pH of 5.80, what is the hydrogen ion concentration?
2. If a solution of aspirin has a [H+] = 1.70 x 10-3 M, what is the pH of the solution?
3. Complete the following chart:
Substance
pH
Coca-Cola
Toothpaste
Blood
Skim milk
pOH
[H+]
[OH-]
2.60
5.44
4.47 x 10-8 M
5.89 x 10-8 M
Acid or Base?
4.
Identify whether each descriptor represents an acid or a base.
a. [H+] = 2.50 x 10-5 M
i.
High concentration of H+ ions
b. [H+] = 5.00 x 10-11 M
j.
High concentration of OH- ions
c. [OH-] = 4.00 x 10-4 M
k. Low concentration of H+ ions
d. [OH-] = 5.00 x 10-10
l.
e. A solution with a high pH
m. pH = 12.0
f.
n. pOH = 12.0
A solution with a low pH
Low concentration of OH- ions
g. Found in fruits
o. Slippery feeling
h. Found in soaps
p. Sour tasting
5. Why does neutral water have a pH of 7?
6. Which solution has a greater hydronium ion concentration, one that has a pH of 4 or one that
has a pH of 8? Explain.
7. A student makes the following statement on an exam: “A solution with pH = 1 is twice as
concentrated in hydronium ions as a solution with pH = 2.”Explain why this statement is not
correct, and write a sentence that describes the correct relationship.