Curls of zinc and magnesium are dropped into 2M hydrochloric acid, and bubbles observer'd.
Video of our demo in action https://youtu.be/6L6t8O4J_Eo
A 600ml beaker, clean and clear, is at the focal point of a camera projecting the image of 500 ml of 2M hydrochloric acid.
A curl of magnesium bubbles wildly, skittering across the surface of the acid.
A curl of zinc sinks to the bottom, and bubbles form at a steady rate.