Hydrogen gas is evolved when hydrochloric acid(HCl) react with HCl it can be summarize asZn+2HCl---------ZnCl2 + H2

Gas evolved when dilute hydrochloric acid reacts with zinc:

When dilute hydrochloric acid reacts with zinc, the gas evolved is hydrogen gas. The reaction can be represented by the chemical equation:

Zn + 2HCl → ZnCl2 + H2

Explanation:

1. Introduction:
Dilute hydrochloric acid is a strong acid that dissociates in water to produce hydrogen ions (H+) and chloride ions (Cl-). Zinc is a reactive metal that can displace hydrogen from acids. When zinc is added to dilute hydrochloric acid, a chemical reaction occurs, resulting in the evolution of hydrogen gas.

2. Reaction:
The reaction between zinc and hydrochloric acid is a redox reaction. Zinc atoms lose electrons and are oxidized to form zinc ions (Zn2+), while hydrogen ions from the acid gain electrons and are reduced to form hydrogen gas (H2).

Zn → Zn2+ + 2e- (Oxidation)
2H+ + 2e- → H2 (Reduction)

3. Formation of zinc chloride:
During the reaction, zinc ions (Zn2+) combine with chloride ions (Cl-) from the hydrochloric acid to form zinc chloride (ZnCl2). This compound remains dissolved in the solution.

Zn2+ + 2Cl- → ZnCl2

4. Evolution of hydrogen gas:
The main product of the reaction is hydrogen gas (H2), which is released as bubbles. Hydrogen gas is less dense than air, so it rises and can be collected over water using the downward displacement of water method.

5. Observations:
When zinc reacts with dilute hydrochloric acid, several observations can be made:
- Effervescence: The production of gas bubbles indicates the evolution of hydrogen gas.
- Fizzing sound: As the gas bubbles escape, a fizzing or hissing sound may be heard.
- Temperature increase: The reaction is exothermic, meaning it releases heat energy. The solution may become warm or hot.

Conclusion:
In summary, when dilute hydrochloric acid reacts with zinc, the gas evolved is hydrogen gas. This reaction is commonly used to generate hydrogen gas in laboratory settings and is an example of a redox reaction.