Question

Which gas is evolved when hydrochloric acid is added in first test tube containing small pieces of marble and then in second test tube containing zinc granules?

Answer 1

We know that when calcium carbonate (CaCO₃) reacts with hydrochloric acid (HCl) then carbon dioxide, calcium chloride and water are formed. So when hydrochloric acid is added in first test tube containing small pieces of marble then CO₂ gas is evolved.

CaCO₃ + 2HCl → CO₂ + H₂O + CaCl₂ 

And when acid reacts with metal then salt and hydrogen (H₂) gas are formed. So when hydrochloric acid is added in second test tube containing zinc granules then H₂ gas is evolved. 

Zn + 2HCl → ZnCl₂ + H₂