Magnesium and Hydrochloric Acid

A small piece of magnesium ribbon is placed in a Petri dish containing 1M hydrochloric acid.  For a large audience presentation, this demonstration should be viewed via a camera or document camera.  Students observe bubbles of hydrogen gas forming.

Curriculum Notes 

There are many places in the curriculum where this demonstration 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 (an oxidation-reduction reaction) when discussing types of reactions. This demonstration may also be performed using a document projector if a dark background is used. Allow about 5 minutes for this demo.  A computer simulation is available to compliment and enhance this demonstration.

Learning Objectives

1. Magnesium metal is an active metal.  Magnesium will react with hydrochloric acid.

2.  Illustration of a single displacement reaction.  Illustration of an oxidation-reduction reaction.  Illustration of a reaction that produces a gas.

3. Write a balanced chemical equation and a net ionic equation.

 

Lead Time 
One day of lead time is required for this project.
Discussion 

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.

The net ionic equation for this reaction is: Mg(s) + 2H+(aq) --> Mg2+(aq) + H2(g)

Materials 
  • Petri dish
  • 1cm strip of magnesium ribbon
  • wash bottle containing 1M HCl
  • forceps
  • overhead projector
  • (Optional) butane fireplace lighter
Procedure 

Mechanics of presenting this demonstration

 

Turn on the camera and focus it. Place the Petri dish on the overhead projector. Pour hydrochloric acid into the Petri dish to a depth of about 5 mm. 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.

Safety Precautions 

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.

Footnotes 

1. B.Z. Shakhashiri; Chemical Demonstrations: A Handbook for Teachers of Chemistry; Wisconsin; 1985; Volume 1; p. 25-26.

© Copyright 2012 Email: Randy Sullivan, University of Oregon Chemistry Department and UO Libraries Interactive Media Group