Reactivity of magnesium. Test tubes containing a strip of magnesium ribbon in four solutions of varying pH. From left to right: hydrochloric acid, ethanoic (acetic) acid, water (pH neutral) and sodium hydroxide (alkaline). Magnesium reacts readily in acids. Therefore bubbles are visible in the first two tubes with the rate of reaction being proportional to the number of bubbles produced. No reaction is visible in the second two tubes.