Page 120 - Science Course 2 (Book 1)

Mo4-L3b: What is the pH of a Solution?

All acid and base solutions contain both hydronium The pH scale is used to indicate how acidic or basic
and hydroxide ions. In a neutral solution, such as a solution is.
water, the concentrations of hydronium and
hydroxide ions are equal.

Acids have a greater concentration of hydronium
ions than hydroxide ions.

Bases have a greater concentration of hydroxide
ions than hydronium ions.

The pH scale contains values that range from
H + OH – pH Scale below 0 to above 14.
1.0 1 x 10 –14
0.1 1 x 10 –13 Acidic
0.01 1 x 10 –12
0.001 1 x 10 –11
1 x 10 –4 1 x 10 –10 On the pH scale acids have a pH below 7.
1 x 10 –5 1 x 10 –9 Bases have a pH above 7.
1 x 10 –6 1 x 10 –8
1 x 10 –7 1 x 10 –7 Neutral Solutions that are neutral have a pH of 7—they are
1 x 10 –8 1 x 10 –6 neither acidic nor basic.
1 x 10 –9 1 x 10 –5 A change in one pH unit represents a tenfold change
1 x 10 –10 1 x 10 –4 in the acidity or basicity of a solution.
1 x 10 –11 0.001
1 x 10 –12 0.01
1 x 10 –13 0.1 Alkaline
1 x 10 –14 1.0

The pH scale helps classify solutions as acidic or
basic.
Key Concept

What is the pH of a Solution?

How does concentration of hydronium ions affect
pH?

How is pH measured?

An indicator is a compound
that changes color at different
pH values when it reacts with
acidic or basic solutions.

There are many different
indicators—each indicator
changes color over a
specific range of pH
values.

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