Reactivity 3.2.4 — Reactions of Acids with Reactive Metals

Acids react with reactive metals to release hydrogen gas. This is a redox reaction where the metal is oxidized and hydrogen ions from the acid are reduced. These reactions help us understand the reactivity of metals and their ability to donate electrons.

General Reaction:

\( \text{Metal} + \text{Acid} \rightarrow \text{Salt} + \text{Hydrogen gas} \)

This is a redox reaction. The metal atoms lose electrons (oxidation), and the hydrogen ions from the acid gain electrons to form \( \text{H}_2 \) gas (reduction).

Example General Equations:

• With hydrochloric acid (HCl):
  \( \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 \)
• With sulfuric acid (H₂SO₄):
  \( \text{Zn} + \text{H}_2\text{SO}_4 \rightarrow \text{ZnSO}_4 + \text{H}_2 \)

Oxidation and Reduction:

• Oxidation (metal): The metal loses electrons.
  \( \text{Zn} \rightarrow \text{Zn}^{2+} + 2e^- \)
• Reduction (acid): Hydrogen ions gain electrons.
  \( 2\text{H}^+ + 2e^- \rightarrow \text{H}_2 \)

Conditions:

• Only reactive metals (e.g., Mg, Zn, Ca) react readily with dilute acids.
• Metals below hydrogen in the reactivity series (e.g., Cu, Ag) do not react with dilute acids under normal conditions.

Types of Acids Commonly Used:

• Dilute hydrochloric acid (HCl)
• Dilute sulfuric acid (H₂SO₄)
• Dilute nitric acid (HNO₃) — usually forms nitrate salts

Predicting Salt Formed:

The salt formed depends on the metal and the acid:

Redox Process Summary:

• Metal is oxidized: Loses electrons → forms cation
• H⁺ is reduced: Gains electrons → forms H₂ gas
• Redox reaction overall: Transfer of electrons from metal to H⁺