Answer:
The preference of zinc over magnesium in the preparation of hydrogen gas is due to the reactivity of these metals with acid. Zinc reacts with acid to produce hydrogen gas more readily compared to magnesium.
When zinc reacts with an acid, such as hydrochloric acid (HCl) or sulfuric acid (H2SO4), it undergoes a displacement reaction, where zinc displaces hydrogen from the acid to form zinc chloride (ZnCl2) or zinc sulfate (ZnSO4) and hydrogen gas (H2).
The chemical equation for the reaction between zinc and hydrochloric acid can be represented as:
Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
On the other hand, magnesium reacts with acid, but it does so at a slower rate compared to zinc. This is because magnesium has a stronger bond with oxygen in its oxide layer, which makes it less reactive.
Therefore, if the goal is to produce hydrogen gas efficiently and quickly, zinc is preferred over magnesium.