Why do acids react with active metals to produce hydrogen?
Active metals react with acids to produce hydrogen because they are above hydrogen in the activity series.
Atoms are always competing with each other for valence electrons.
Active metals readily lose their valence electrons to form cations. For example,
Na → Na⁺ + e⁻
Hydrogen "wants" those electrons.
2H⁺ + 2e⁻ → H₂
So an active metal reacts with acids to produce hydrogen.
2Na + 2H⁺ → 2Na⁺ + H₂
Metals below hydrogen in the activity series are even less willing to give up their valence electrons. Instead, their ions remove valence electrons from hydrogen to form the metal atoms. For example,
H₂ → 2H⁺ + 2e⁻
Cu²⁺ + 2e⁻ → Cu
H₂ + Cu²⁺ → 2H⁺ + Cu
The video shows an experiment to determine the placement of three different metals (Cu, Zn and Mg) on the activity series.
Video from: Noel Pauller"