A PENNY'S WORTH OF HYDROGEN
In this experiment, students generate
hydrogen using inexpensive materials.
This experiment is suitable for a
general or first-year college-prep course. By placing a prepared penny in
hydrochloric acid, students are able to observe the evolution of hydrogen. If
the mass of the penny is determined before and after reaction, students may
determine the percent of zinc in the penny and/or the mass and volume of
hydrogen produced from the penny.
Fifteen to twenty minutes on two
Concentrated solutions of HCl will burn
skin and damage clothing. Fumes from acid can be caustic and/or irritating; do
this experiment in a well-ventilated area (hood, if available). Goggles must be
worn throughout this experiment.
- 6 M HCl solution (500 mL
concentrated HCl solution diluted to 1.00 L distilled or deionized water)
- 250-mL breaker
- triangular file
- graduated cylinder
- HCl solution is available from a hardware store as muriatic acid, 28% HCl.
This solution is approximately 8 M and may be substituted for 6 M HCl solution.
- A wide-mouth jar may be substituted for the beaker.
- If a triangular file is not available, the penny may be scratched by
scraping it on a brick, cement block, or the sidewalk.
- Using a triangular file, make several small notches on the edge of the
penny. The zinc color should be evident.
- In a well-ventilated area or fume hood, place the penny in a 250-mL beaker
and cover it with 25 mL of 6 M HCl solution. Use separate beakers if more than
one penny is to be used.
- Observe the evolution of gas as the reaction proceeds.
- Allow the reaction to continue overnight.
- The next day, or when the evolution of gas has stopped, carefully pour acid
into sink while cold water is running. Using forceps, carefully remove hollow
penny from beaker without crushing it. Fill beaker with water and return penny
to beaker to remove all traces of acid.
- Carefully remove the penny and allow it to air dry.
- If the experiment is to be done quantitatively, include the following
- Mass penny before the reaction.
- Mass dry penny after the reaction
- Calculate the percent of zinc in the penny.
- Calculate the mass and volume of hydrogen at STP produced from the penny.
Acid solution may be flushed down the
drain with water. Pennies may be disposed of with solid waste.
Two reactions occur:
Herman, R.A., Chem 13 News, 146 (1984).
- Any copper oxide on the surface of the penny reacts with HCl (aq) according
to the following reaction:
CuO (s) + 2 HCl (aq) ----> Cu2+(aq) + 2 Cl-(aq) +
- The zinc core of the penny reacts with HCl(aq) according to the following
Zn (s) + 2 HCl (aq) ----> Zn2+(aq) + 2 Cl- (aq) + H2 (g)
coating over the zinc does not react with the acid. When all of the zinc has
dissolved, the hollow penny may float if gas bubbles are trapped within the
Submitted by Patricia Noel
Woodrow Wilson Leadership Program in Chemistry
The Woodrow Wilson National Fellowship Foundation
CN 5281, Princeton NJ 08543-5281