Introduction: (Initial Observation)
Most metals that we see around are not very active. It takes some time for them to rust or show reaction to corrosive liquids.
There are other metals however that we don’t have around and they are so reactive that they can burn violently simply by being exposed to air or water.
Some metals such as gold never rust and are never affected by regular corrosive substances.
To protect metal products from chemical reactions and rusting, we cover them with protective coatings such as paint.
We also sometimes cover a metal with another less active metal by a process called electroplating. For example, a copper piece plated with gold does not rust because in such a piece, it is gold that is exposed to air and moisture, not copper.
Find out about metals reactivity and how the variations in the reactivity of different metals may affect chemical reactions. Read books, magazines, or ask professionals who might know in order to learn how variations in activity of metals is beneficial for certain chemical reactions. It is also good if you ask or read about electroless plating and see if you find any relation between the activity of metals that are plated and the activity of their base metal. Keep track of where you got your information from.
The following are samples of information that you may find.
activity series of metals
Activity series of metals is a listing of metals (and hydrogen) in order of decreasing activity. The activity or electromotive series of metals is a listing of the metals in decreasing order of their reactivity with hydrogen-ion sources such as water and acids. In the reaction with a hydrogen-ion source, the metal is oxidized to a metal ion, and the hydrogen ion is reduced to H2. The ordering of the activity series can be related to the standard reduction potential of a metal cation.
|Oxides are not reduced to the metal by hydrogen.||Li
|React with cold water liberating hydrogen.||React with steam liberating hydrogen.||React with acids liberating hydrogen.||React with oxygen giving oxides.|
|Oxides are reduced to the metal by hydrogen.||Fe
|Oxides are decomposed by heat alone.||Hg
activity series: also known as the Electromotive Force Series. This is a listing of the elements according to their potential differences and ability to place other elemental ions in solution.
Note: Gathered information shows that Lithium is the most active metal, not potassium as expressed in the project title.
The Activity Series of the metals is an invaluable aid to predicting the products of replacement reactions. It also can be used as an aid in predicting products of some other reactions. Pay attention to the notes below as they are provided to help you make better use of the activity series than just the list of metals by themselves.
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 project is to rank order several metals on the basis of their chemical activity. The metals that will be tested are: Iron, Copper, Zinc and Aluminum.
The above sample metals are selected based on their availability and safety. You can select any other group of metals for your experiment if they are available to you. Find and review some general and safety information for each metal that you are including in your study. If you are a beginner or you don’t have access to sufficient safety and laboratory equipment, please avoid using metals such as sodium, potassium, lithium and calcium that cause flame and explosive reactions with water.
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.
The independent variable is the type of metals that we test (possible values are Iron, Copper, Zinc and Aluminum.)
Dependent variable is the rate at which bubbles of hydrogen are produced.
Controlled variables are temperature, acid concentration, metal surface area and experiment procedures.
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis. Following is a sample hypothesis:
Subject metals can be ranked with Iron as the most active metal followed by copper, zinc, and finally aluminum as the least active metal. My hypothesis is based on my gathered information that the activity of metals increase from right to left and from top to bottom in the periodic table of elements.
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.”
Experiment 1: Compare the activity of Iron, Zinc, Aluminum and Copper
Active metals react with water or acids to produce hydrogen gas. The rate at which bubbles of hydrogen are produced when various metals are placed in water or acid solution can be used to indicate the reactivity of the metals. Metals in the first and second groups of the periodic table can react with water; however the metals that we have selected do not react with water, so we use hydrochloric acid for our experiment.
Material and Equipment:
Iron, Zinc, Copper and Aluminum metal samples
Get identical or very similar metal samples with identical or very similar surface areas. Samples can be from sheet metals, pipes, rods or similar objects. Zinc pieces may be available at MiniScience.com; however if you can not find pure zinc, use galvanized iron instead of zinc. Galvanized iron is coated by zinc and serves the purpose for a quick experiment.
6 M HCl solution (500 mL concentrated HCl solution diluted to 1.00 liter with distilled or deionized water)*
test tubes or small beakers*
*HCl solution is available from a hardware store as muriatic acid, 28% solution; this solution is approximately 8 M and may be substituted for 6 M HCl solution.
Styrofoam cups or small glass jars may be used in place of test tubes or small beakers.
- Wash all samples with warm water, liquid detergent and brush. Avoid touching samples.
- Place a different metal in each of four test tubes and add just enough 6 M HCl solution to cover the metal.
- Record the relative activity of each metal based upon the rate at which hydrogen is released.
- Test the gas released by the galvanized nail with a burning splint to confirm that it is hydrogen.
- Rank the four metals from lowest to highest activity.
Some metals form an oxide coating on the surface that will prevent further oxidation; these should be cleaned with steel wool before testing their reactivity. Even though the metals chosen for this experiment may have an oxide coating, they should give the correct order of activity without cleaning because of the large differences in activity.
Dilute the acid with water and flush down the drain with water. Metal pieces can be discarded 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.
Experiment 2: (Optional) Compare the activity of Magnesium and Calcium
If the metals that you are comparing their activity do react with water, you must perform your experiment using water instead of acid. The purpose of this experiment is to compare the activity of two metals in the same group and infer predictions of the activity of other metal and nonmetal groups. In this experiment we use the chemical phenolphthalein to test if a compound is a base. Phenolphthalein will turn bright pink or fuchsia when placed in a base. You could use other pH indicators instead of phenolphthalein. Metals in group 2 of periodic table of elements are relatively safer than metals in group one; however you should know that metals such as magnesium are used in making fire bombs and fire work displays and extreme cautious is required in storing and handling them. In this experiment also you need to controlled variables such as surface area of sample metals, temperature, amount of water, amount of phenolphthalein and experiment procedures.
- Get two 400 ml beakers and add 200 ml distilled water in each beaker.
- Add a few drops of phenolphthalein solution to each beaker.
- Label each beaker with the name of metal that you are testing in that beaker
- Drop your metal samples (calcium and magnesium) in beakers as labeled.
- Heat up both beakers in a hot water bath.
- Observe the rate of color change caused by formation of hydroxide in beakers.
The reaction of Ca and water produced a base. This was evident because the phenolphthalein reacted with the product to give it a bright pink coloring.
The reaction of Mg and water produced a weak base. The base was not produced until the water reached a boiling temperature and the phenolphthalein turned a faded pink.
Ca is more chemically active than Mg. The Mg was less reactive requiring the water to be boiling to react with it. A similar proportion of phenolphthalein turned the Ca product a bright pink and added a light tinge to the Mg.
The activity of metals in a group is greater for those with a larger number of protons and less for elements with fewer. Nonmetals behave in the opposite way. The most active nonmetal is that with the fewest protons and the least active is the nonmetal containing the most protons.
Materials and Equipment:
List of material can be extracted from the experiment section. Final list of material for your experiment may vary based on the metals that you choose to test and the equipment that you may choose to use. For example you may substitute a beaker with a test tube, a glass cup, a glazed ceramic cup, a plastic cup or even a Styrofoam cup.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Write which metal created hydrogen bubbles at a higher rate.
Not needed for this project.
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.
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. Following is a sample conclusion:
Active metals react with acids to produce hydrogen. In the reaction, the metal is oxidized while the H+ from the acid is reduced to H2(g). The most active metals are the most easily oxidized. In our experiment the rate of hydrogen formation in aluminum was the highest. So, aluminum is the most active, followed by zinc, iron, and copper. My hypothesis was incorrect.
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.
Answer the following questions after completing this experiment:
- What is one problem associated with acid rain that is illustrated by this experiment?
- What other problems are associated with acid rain?
- Some metals are galvanized to prevent “rusting.” If zinc reacts with acid readily, as discovered in this experiment, why is iron coated with zinc?
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.