Page 112 - Chemistry_Form_2

Chemistry
for Secondary Schools

Questions
1. What are the balanced chemical equations for the reaction between:

(a) zinc and dilute hydrochloric acid?
(b) zinc and dilute sulfuric acid?
FOR ONLINE READING ONLY
(c) magnesium and dilute hydrochloric acid?
(d) magnesium and dilute sulfuric acid?

2. What causes the observations recorded in Step 3 of the experiments? Support
with balanced chemical equations.

3. What happened in Steps 2 and 3 when lead and copper were used in the
experiment? Write the balanced chemical equations for the reactions of these
metals with sulfuric acid.

Task 5.2

Use virtual laboratories or interactive simulations and animations to explore the
strength and the basicity of acids.

Strengths of acids
The strength of an acid is a measure of its ability to ionise (dissociate) in water
to produce hydrogen ions (H ). The more the acid ionises in water, the stronger it
+
is. The strength of the acid solution can be determined by its pH value. The pH is
the measure of the degree of acidity or alkalinity of the solution. Based on their
strengths, acids are grouped into strong acids and weak acids.

Strong acids ionise completely in water to give large amounts of H . This
+
complete ionisation makes them highly reactive. Common examples of strong
acids are mineral acids such as hydrochloric acid, nitric acid, and sulfuric acid.
For example, hydrochloric acid ionises completely in water to give H and Cl .
−
+

Weak acids ionise partially in water to produce small amounts of H . This
+
means that not all acid molecules release H . Common examples of weak acids
+
are ethanoic acid, carbonic acid, and citric acid. For example, ethanoic acid
(CH COOH) ionises partially in water to produce few CH COO and H .
+
─
3
3

Student’s Book Form Two 105

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CHEMISTRY FORM TWO NEW 2025 DUMMY.indd 105