Name the gas generally liberated when an acid react with metal. Illustrate with an example. How you test this gas in your laboratory ?
Answers
HELLO THERE!
That's simple:
Active metal + Dilute Acid ----> Respective Salt + Hydrogen.
Hence, the gas evolved when an acid reacts with metal is Hydrogen.
Examples:
2Na + 2HCl -----> 2NaCl+ H₂
Zn + H₂SO₄ -----> ZnSO₄ + H₂
Note: Nitric acid is an exceptional acid, because of its high oxidizing power. So, it does not react with active metals to liberate hydrogen gas, as it oxidizes the hydrogen formed to water, and hence we get no hydrogen. Only 1-2% Nitric acid (very dilute) reacts with Manganese or Magnesium to produce Hydrogen gas.
Mg + 2HNO₃ -----> Mg(NO₃)₂ + H₂
Now, your question asks for the test of Hydrogen gas. Here are some tests:
=> Hydrogen gas burns in air with a pale blue flame and a pop sound.
=> When hydrogen is brought to air, it forms tiny water droplets, when it reacts with the oxygen present in the air.
=> When chlorine gas is reacted in diffused sunlight, and ammonia solution is brought near it, we get dense white fumes. Check out the reactions involved:
H₂ + Cl₂ ----> 2HCl
HCl + NH₄OH -----> NH₄Cl + H₂O
NH₄Cl formation gives dense white fumes.
THANKS!