Magnesium and Hydrochloric Acid
A small piece of magnesium ribbon is placed in a Petri dish containing 1M hydrochloric acid on the overhead projector. Students see bubbles of hydrogen gas forming.
There are many places in the curriculum where this demo could be used. it is most commonly used when discussing the characteristic reactions of either metals or acids. It's also a great example of a single replacement reaction when discussing types of reactions. This demo may also be performed using a document projector if a dark background is used. Allow about 5 minutes for this demo.
Magnesium reacts with hydrochloric acid according to the equation: Mg (s) + 2 HCl (aq) --> MgCl2 (aq) + H2 (g) This demonstration can be used to illustrate the characteristic reaction of metals with acid, a single replacement reaction, or to demonstrate the generation of hydrogen gas. The flammability of hydrogen gas can be demonstrated by carefully holding a match or fireplace lighter up to the popping hydrogen bubbles. An audible crackling sound is heard as the hydrogen burns.
- Petri dish
- 1cm strip of magnesium ribbon
- wash bottle containing 1M HCl
- overhead projector
- (Optional) butane fireplace lighter
Place the Petri dish on the overhead projector. Pour hydrochloric acid into the Petri dish to a depth of about 5mm. Turn on the projector and focus it. Using forceps, place the magnesium ribbon into the Petri dish. The magnesium reacts with the acid, producing visible bubbles of hydrogen gas.
(Optional) If the flame of a butane fireplace lighter is held above the bursting bubbles, they will produce audible pops as the hydrogen ignites.
Magnesium ribbon is a flammable solid. Hydrochloric acid is a corrosive liquid. Hydrogen gas is explosive. However, the very small quantities and low dilutions used in or produced by this demo present little hazard. Wear safety goggles. Keep flammables and open flame away from the vicinity of the demo.