The Action of Metallic Acids

Introduction

Metallic acids are a subclass of inorganic acids where the central atom is a metal. Most commonly, these include acids such as chromic acid (H₂CrO₄), vanadic acid (H₃VO₄), and permanganic acid (HMnO₄). Though less common in daily life than non-metallic acids, metallic acids are widely used in industry and research.

Characteristics of Metallic Acids

• Metallic acids are generally strong oxidizing agents.
• They often participate in redox reactions with a variety of substances.
• The acid strength and oxidizing power depend on the metal and its oxidation state.

Action on Metals

Metallic acids often react vigorously with metals, especially those that are easily oxidized. This is because these acids supply both protons (H+) and strong oxidizing anions (e.g., Cr₂O₇2-, MnO₄-).
For example:

In some cases, as with permanganic acid, the reaction with metals can additionally release oxygen, confirming their strong oxidizing nature.

Action on Non-metals and Organic Matter

Due to their oxidizing ability, metallic acids can also react with non-metals (like sulfur, phosphorus) and organic compounds to oxidize them. This makes them valuable as cleaning agents in laboratories and as industrial oxidants.

Action on Bases and Alkalis

Metallic acids neutralize bases to form the corresponding metallic salts and water. For example:
H₂CrO₄ + 2 NaOH → Na₂CrO₄ + 2 H₂O

• The reaction is similar in principle to other acid-base neutralization reactions, except the salt contains a metallic acid anion.
• These salts are often brightly colored (e.g., chromates are yellow).

Environmental & Practical Considerations

Many metallic acids are hazardous or toxic due to the nature of their central metals (e.g., chromium, manganese in high oxidation states). Special care must be taken in handling, disposal, and environmental release.

Summary Table: Actions of Common Metallic Acids