Which gas is usually liberated when an acid reacts with a metal

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Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?

Answer: Hydrogen gas is liberated when an acid reacts with a metal.
Take few pieces of zinc (Zn) granules in a delivery tube.  Add 5ml of hydrochloric acid (HCl). White fumes will rise. Pass the gas to a soap solution or collect it in a balloon (as shown in the following video). The gas collected is Hydrogen gas. Since H2 gas has lower density as compared to air, the balloon will float in air.

Zn (s) + 2HCl (aq) → ZnCl2(s) + H2 (g)

You can test the evolved hydrogen gas by its burning with a pop sound when a candle is brought near the balloon (or soap bubbles).

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