Introduction: (Initial Observation)
US penny has a long history and it has gone through changes mainly in it’s alloy or metallic composition. Pennies are no longer made from copper. Pennies are made of zinc and they are just coated with a thin layer of copper.
Zinc can easily react with cold acids and release hydrogen gas. In this project I want to see how much hydrogen can be made using the zinc in a penny.
I also want to find out what percent of penny is zinc.
Information Gathering:
Find out about the reaction of acids and metals. Read books, magazines or ask professionals who might know in order to learn about different acids, their applications and availability. Keep track of where you got your information from.
Hydrochloric acid is used as a cleaner and can be purchased from hardware stores. It is also known as muriatic acid, but this name is obsolete now.
Following are samples of information that you may find online:
The Activity of Metals
The primary difference between metals is the ease with which they undergo chemical reactions. The elements toward the bottom left corner of the periodic table are the metals that are the most active in the sense of being the most reactive. Lithium, sodium, and potassium all react with water, for example. The rate of this reaction increases as we go down this column, however, because these elements become more active as they become more metallic.
Source Purdue University Website, Chemistry Department
Hydrogen Fueled Cars:
To show a purpose or application to produce hydrogen, you may search the Internet for hydrogen fuel, and find documents discussing future uses of hydrogen as a source of clean fuel.
Question/ Purpose:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this investigation is to find out:
- How much hydrogen gas can be produced by the reaction of an acid and a US penny?
- What percentage of US penny is zinc?
Identify Variables:
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
Based on the purpose that we defined for this project, we will not need to define variables. We will also not have any results table and graph. If you like to do an experiment that requires a results table and a graph, you can add another question as follows:
How does the temperature of acid solution affects its rate of reaction with zinc?
Of course you will then need to use pure zinc for your experiment and you will not be able to use pennies. If you select this question, your independent variable is the reaction temperature. The dependent variable is the rate of reaction. Controlled variables are the concentration of acid, the size and shape of zinc pieces that you test, as well as other procedure and environmental conditions.
Hypothesis:
Based on your gathered information, make an educated guess about the amount of hydrogen gas that you can produce using a penny. Also make a guess about the percent of zinc in pennies.
This is a sample hypothesis:
Each penny may produce about 1 liter of Hydrogen gas. I also think that about 80% of the penny is Zinc.
Experiment Design:
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Introduction:
By placing a prepared penny in hydrochloric acid, you are able to observe the evolution of hydrogen. If the mass of the penny is determined before and after reaction, you may determine the percent of zinc in the penny and/or the mass and volume of hydrogen produced from the penny.
Procedure:
- 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 steps:
- 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 produced from the penny.
8.Acid solution may be flushed down the drain with water. Pennies may be disposed of with solid waste.
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.
Materials and Equipment:
Chemicals:
- 6 M HCl solution (500 mL concentrated HCl solution diluted to 1.00 L distilled or deionized water)
- penny
Equipment:
- 250-mL breaker
- triangular file
- graduated cylinder
- forceps
- balance
- 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.
Note: 6 M means 6 Mole or (6 molecule-gram per liter). Molecular weight of HCl or Hydrochloric acid is 36.5 grams. So the 1 M solution of hydrochloric acid is a 36.5 gram per liter solution. 6 M solution must be 6 times more concentrated, so it should have 6×36.5 grams of hydrochloric acid per liter (that is 219 grams/Liter).
Usually a very strong solution of hydrochloric acid is 12 Mole, so you can dilute it to 6 Mole by adding water.
Results of Experiment (Observation):
Two reactions occur:
- Any copper oxide on the surface of the penny reacts with HCl (aq) according to the following reaction:
CuO (s) + 2 HCl (aq) —-> Cu 2+(aq) + 2 Cl-(aq) + H2O (l)
- The zinc core of the penny reacts with HCl(aq) according to the following reaction:
Zn (s) + 2 HCl (aq) —-> Zn2+(aq) + 2 Cl- (aq) + H2 (g)
The copper 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 shell.
Calculations:
First you calculate the weight of zinc in a penny. Then using the second formula above and the atomic weight of all elements, you may calculate the amount of Hydrogen gas that is released using that amount of zinc.
Details:
A simplified reaction formula for reaction of zinc and Hydrochloric acid is shown below.
Zn + 2 HCl —-> Zn Cl2 + H2
This formula simply means that each molecule of zinc will react with 2 molecules of acid and produces one molecule Zinc Chloride and One molecule hydrogen gas.
Using the atomic mass and molecular masses of the above components, we can rephrase the above statement as follows.
65.37 grams zinc reacts with 73 grams of hydrochloric acid to make 136 grams Zinc chloride and 2 grams of hydrogen.
So each 65.37 grams of zinc produces 2 grams of Hydrogen. You may also know that 2 grams of hydrogen is 22.4 liters. (Volume of one mole of any gas is 22.4 Liters at STP*)
So 65.37 grams of Zinc Produces 22.4 Liters of hydrogen gas.
* standard temperature and pressure
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Conclusion:
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Possible Errors:
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
References:
Herman, R.A., Chem 13 News, 146 (1984).
Any Inorganic Chemistry book can be used as reference for this project.
Purdue University Website , Chemistry Department
