Page 113 - Chemistry_Form_2

Chemistry
for Secondary Schools

Note:
(a) The pH values of solutions increase with decrease in acidity; therefore, weak
acids have higher pH values than strong acids.
(b) Solutions of strong acids are good conductors of electricity because they
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contain more free mobile ions to carry the charges than solutions of weak
acids.

Basicity of an acid

Basicity of an acid is the number of ionisable hydrogen atoms per molecule of the
acid that can be displaced by a metal in solution. For example, hydrochloric acid
is monobasic as it has one ionisable hydrogen atom that can be displaced. Sulfuric
acid and phosphoric acid are dibasic and tribasic, respectively. Sulfuric acid has two
ionisable hydrogen atoms, while phosphoric acid has three ionisable hydrogen atoms
that can be displaced (Table 5.2).

Table 5.2. Basicity of some acids
Acid Basicity
Monobasic

Dibasic

Tribasic

Exercises 5.1

1. Describe how the degree of ionisation leads to differences in acidic strength.

2. Should the strength of an acid be the only factor in determining its use in
industry, home or laboratory? Explain your answer.

3. A particular skincare product contains glycolic acid. Why is it important to
know the strength of the acid before using it on the skin?
4. Why do the physical properties of acids make them suitable for cleaning
products?

Bases
A base is a substance that neutralises an acid by reacting with hydrogen ions.
Bases include the oxides, hydroxides, and carbonates of metals.

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