Zinc reaction with a weak (left) and a strong acid compared. In the weak acid, few bubbles of hydrogen are seen. This is because metallic zinc in air reacts with atmospheric carbon dioxide to form a passivating layer of zinc carbonate which is resistant to weak acids. Strong acids are able to dissolve the passivating layer, so the reaction is more vigorous. The reaction of zinc in acid is given by the equation Zn (s) + 2H+ (aq) = Zn2+ (aq) + H2 (g).