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pH Scale
2-27-12
Standard: 5d-students know how to use the pH
scale to characterize acid and base solutions
The pH Scale

The pH of a solution is a measure of its
hydronium ion concentration.
The pH scale is a number scale from 0
to 14 to describe the concentration of
hydronium ions in a solution.
 A pH of 7 indicates a neutral solution.
 Acids have a pH less than 7.
 Bases have a pH greater than 7.

If you add an acid to water, the
concentration of H3O+ increases and the
concentration of OH- decreases.
 The lower the pH value, the greater
the H3O+ ion concentration in
solution is.

If you add a base to water, the
concentration of OH- increases and the
concentration of H3O+ decreases.
 The higher the pH value, the lower
the H3O+ ion concentration is.

Example
Substance A has a pH of 3. Substance B
has a pH of 10.
 Is the substance A considered acidic or
basic? Is substance B considered acidic
of basic?
 From this does this mean there are
more hydronium ions present or
hydroxide ions present for substance
A? Substance B?
 From Friday does this mean your
substances are weak or strong acids or
bases?

Try it on your own
Substance A has a pH of 5,
Substance B has a pH of 9.
 Is substance A and B considered
acidic of basic?
 From this does this mean there are
more hydronium ions present or
hydroxide ions present for substance
A? Substance B?
 Are substance A and B weak or
strong acids or bases?

Exit Question
a) What does the pH scale measure?
 Given the following pH numbers is
the sample a base, acid, or neutral?
 A) 6
 B) 12
 C) 7
 Please include a reflection on how
you feel about your activity today.
