Short Answer

When an acid reacts with a metal, it produces a salt and hydrogen gas. The reaction is usually vigorous and releases bubbles of hydrogen.

For example, zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas:
Zn + 2HCl → ZnCl₂ + H₂
The reaction depends on the reactivity of the metal and the strength of the acid.

Detailed Explanation :

Reaction of Acids with Metals

Metals react with acids to release hydrogen gas and form salts. This is a type of single displacement reaction, where the metal displaces hydrogen from the acid. Not all metals react; only metals more reactive than hydrogen in the reactivity series take part in this reaction.

The general equation is:

Metal + Acid → Salt + Hydrogen gas

Examples of Acid-Metal Reactions

1. Zinc + Hydrochloric acid:
   Zn + 2HCl → ZnCl₂ + H₂

• Produces zinc chloride (salt) and hydrogen gas.
• Visible as bubbles of gas.

1. Magnesium + Sulfuric acid:
   Mg + H₂SO₄ → MgSO₄ + H₂

• Produces magnesium sulfate (salt) and hydrogen gas.

1. Aluminium + Hydrochloric acid:
   2Al + 6HCl → 2AlCl₃ + 3H₂

• Produces aluminium chloride and hydrogen.

Mechanism of the Reaction

1. Metal atoms lose electrons to form metal cations:
   M → M²⁺ + 2e⁻
2. Hydrogen ions (H⁺) from the acid gain electrons to form hydrogen gas:
   2H⁺ + 2e⁻ → H₂

This explains the release of hydrogen gas during the reaction.

Factors Affecting the Reaction

1. Reactivity of the Metal

• More reactive metals (like Na, K, Ca) react violently.
• Less reactive metals (like Cu, Ag, Au) may not react at all with dilute acids.

2. Type of Acid

• Strong acids (HCl, H₂SO₄, HNO₃) react faster.
• Weak acids (CH₃COOH) react slower.

3. Concentration and Temperature

• Higher concentration → faster reaction.
• Higher temperature → faster reaction due to increased kinetic energy.

Observations During Reaction

1. Bubbles of hydrogen gas appear on the metal surface.
2. Heat may be released (exothermic reaction).
3. Metal dissolves gradually, leaving behind the salt in solution.
4. Effervescence is visible due to hydrogen gas formation.

Applications of Acid-Metal Reactions

1. Hydrogen Gas Production

• Laboratory preparation of hydrogen uses reactions of metals with acids.
• Example: Zn + HCl → H₂ + ZnCl₂

2. Metal Cleaning

• Acids remove rust (Fe₂O₃) or scale from metals.
• Example: Pickling of steel uses HCl.

3. Salt Preparation

• Salts can be prepared by reacting metals with acids.
• Example: Zn + H₂SO₄ → ZnSO₄ + H₂

4. Educational Demonstration

• Shows reactivity series and single displacement reactions.

Safety Precautions

1. Hydrogen gas is flammable, so avoid sparks or flames.
2. Handle acids with gloves and goggles.
3. Conduct experiments in well-ventilated areas.

Summary of Reaction

• Metal + Acid → Salt + Hydrogen gas
• Metals above hydrogen in reactivity series react.
• Strong acids and reactive metals give vigorous reactions.
• Observations: effervescence, metal dissolving, heat release.
• Applications: hydrogen production, salt preparation, cleaning metals.

Conclusion

When an acid reacts with a metal, a salt and hydrogen gas are produced. The reaction is exothermic and depends on the reactivity of the metal and the strength of the acid. Vigorous bubbling indicates hydrogen release. This reaction is widely used in laboratories, industry, and metal cleaning, as well as in the production of hydrogen gas. It also demonstrates the reactivity series of metals and the principle of single displacement reactions.