
I can explain the pH scale.
Definition:



a measure that shows the acidity of a solution
also sometimes called the “power of
hydrogen”
(recall: hydrogen ions are part of acids)
the pH scale ranges from 0 – 14
0
1
strong
acid
High
[H+]
2
3
4
5
6
weak
acid
7
8
9
10
weak
base
12
13
14
strong
base
NEUTRAL
([OH-] = [H+])
Low
[H+]
11
Low
[OH-]
High
[OH-]
How is the pH scale formed?
The pH scale is formed according to the
concentration of hydrogen ions (H+) found in
a solution.
The more H+ there are, the more acidic the
solution. Likewise, the fewer H+ there are,
the more basic the solution.
pH: A Logarithmic Scale
The pH scale is a logarithmic scale.
This means that every change of one unit on
the scale represents a 10-fold effect on the
concentration of the solution.
(i.e. Every time you move up or down the pH
scale by 1 “pH unit”, the concentration
changes by 10x.)
For example:


A solution with pH 4 is 10 times more acidic
than pH 5, and is 100 times more acidic than
pH 6.
Therefore, pH 4 has 10 times more H+ than
pH 5, and 100 times more H+ than pH 6.
Although the concentration of hydrogen ions
(H+) is measured in the pH scale, hydroxide
ions (OH-) are also present at any point along
the pH scale. (Recall that OH- are part of
basic solutions.)
Practice:
If the pH of a solution is changed from pH 6 to pH
10, what type of solution was it originally? What
type of solution did it change to?
pH 6
weak acid
pH 10
weak base
How much stronger or weaker has the solution
become?
The solution became a stronger base by 10,000x.
(10,000x more OH- ions)
OR
The solution became a weaker acid by 10,000x.
(10,000x more H+ ions)

I can state the pH range for acids and the pH
range for bases.