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Activities of Metals.

Activities of Metals.

Introduction: (Initial Observation)

I started studying this subject when I first saw the magical demonstration of a street vendor who would turn copper pennies to shiny and white silver like coins. He was simply rubbing the pennies with a piece of cloth and a drop of a clear liquid that he was selling.

Later, I learned that this process is called Electroless plating. Possibly the clear liquid was a solution of a silver salt such as silver nitrite. As this solution gets in contact with copper, the silver in the salt becomes substituted by copper and pure silver is released. This pure silver on the surface of the penny is what gives it the metallic shine of silver. Solution will gradually change to copper nitrate when there are no more silvers to be released. Later, I learned that a similar method is used to make mirrors. What you see in the back of mirrors is silver, plated by Electroless plating. Finally, I learned that this method can also be used to extract pure silver from the waste water of photography solutions.

It seems that substitution of one metal by another in a solution has many benefits.

Initial studies shows that any metal in a salt solution may be released by another metal that is more active. More active metals have a stronger bond with anions (Anions are atom or group of atoms carrying a negative charge like Cl- , SO4– , and CH3 COO-, …), so they enter the formula and the less active metal will be released. That is almost like the reaction of metals with acids where Hydrogen gas is released. The only difference is that here, another metal will be released instead of hydrogen.

My question is “which metals are more active than others?”. (Or which metals can free other metals from an ionic solution?) If I know the answer to these questions and I have a list of metals ordered by their activity, I will then be able to determine which metals can release other metals from ionic solutions.

In this project I will test a few metals and compare their activity levels.

Dear

This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out how acids react with metals to release Hydrogen gas. Learn about inactive metals that do not react with acids. For the metals that do react with acids, gather information about their activity or their rate of reaction. Read books, magazines, or ask professionals who might know in order to learn about methods that you may use in order to classify metals based on their activity or their ability to enter reactions. Keep track of where you got your information from.

The following are samples of information that you may find.

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.

Some metals such as gold and platinum, do not react with acids. These are called inactive metals.

Active metals react with acids to produce hydrogen gas. The rate at which bubbles of hydrogen are produced when various metals are placed in acid solution can be used to indicate the reactivity of the metals.


 

 

Activity Series:
An activity series is the ranking of metals according to their reactivity.
In an activity series, metals are arranged in order of decreasing ability to lose electrons.
Generally, the more reactive metals are placed at the top of the list. Any metal above hydrogen will displace hydrogen as H2 gas from an acid, and any metal below hydrogen will not displace hydrogen from an acid.

The list on the right is an activity series. Lithium on the top of the list is the most active metal on the list. Gold, which is on the bottom of the list is the least active metal.

Li
K
Ba
Ca
Na
Mg
Al
Mn
Zn
Cr
Fe
Co
Ni
Sn
Pb
H
Cu
Ag
Hg
Pt
Au

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 objective of this experiment is to order several metals on the basis of their chemical activity. The metals that I am selecting for my experiment are Iron, Copper, Zinc, and Aluminum.

I selected these metals because it was easy for me to find them in my local hardware store.

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 are 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 are the type of metals that you test. Values are (Calcium, Copper, Zinc, Magnesium)

Dependent variable is the reactivity of metal that can be ranked visually by observing the speed of hydrogen release.

Controlled variable is temperature.

Constants are:

  • the surface area of metals in each test
  • the type and concentration of acid being used
  • Preparation of metals and experiment method

Hypothesis:

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.

My hypothesis is that calcium is the most active metal in my samples, followed by magnesium and zinc. Copper may show no activity at all.

My hypothesis is based on the activity series that I found on the Internet.

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.”

Experiment:

Rank metals based on their activity

Introduction:

Active metals react with acids to produce hydrogen gas. The rate at which bubbles of hydrogen are produced when various metals are placed in acid solution can be used to indicate the reactivity of the metals.

Safety Notes:

Concentrated solutions of HCl will burn skin and damage clothing. Fumes from acids can be caustic and/or irritating; do this experiment in a well-ventilated area. Goggles must be worn throughout this experiment.

Procedure:

  1. Prepare your metals by cutting strips of 1/2″ x 1″ of each metal. Wash the pieces with warm water and detergent to remove any oil from their surface.
  2. Place a different metal in each of four test tubes and add just enough 6 M HCl solution to cover the metal.
  3. Record the relative activity of each metal based upon the rate at which hydrogen is released.
  4. Test the gas released by the galvanized nail with a burning splint to confirm that it is hydrogen.
  5. Rank the four metals from lowest to highest activity.

Experiment Notes:

In this experiment, the rate of hydrogen release per unit of surface varies among different metals, so the pieces do not really have to be the same shape or the same size. You will still be able to tell which metal is reacting at a higher rate. If you do not have access to strips of metals, remove the metal size and surface area from your constants.

I got a strip of Zinc and a strip of Copper from a science kit (Make Electricity Science kit, MiniScience.com). I also got a strip of Aluminum and a strip of Iron from a local metal forming shop. If you are doing the same, do not get the ones that are painted.

If you don not have access to Zinc, just by Galvanized bolts from your hardware stores. They may have it labeled as Zinc. These bolts are coated with Zinc and coating will last about a minute in acid solution. This time is more than enough for you to compare the rate of activity.

Disposal:

Dilute the acid with water and flush down the drain with water. Metal pieces can be discarded with solid waste.

Need a data table and graph?

If you need a data table and graph, you cannot visually compare the activity of metals by looking at the hydrogen bubbles; instead, you must have a method of measurement. You must also keep constant values such as the metal surface, size of the test tubes, amount and the type of acid. You must also control the temperature to make sure that all experiments are performed at the same temperature.

One method of measurement is by using balloons.

Immediately after dropping the metal piece in acid, place the balloon on the test tube and start tracking time. Avoid shaking or tapping the test tube because this may affect the production of hydrogen bubbles and bias the readings.

When the balloon is filled with enough oxygen gas, it will stand up straight. Stop the watch and record the time.

Repeat the above procedure for every other metal.

Your results table may look like this:

Metal name Time to fill up the balloon

Make a graph:

You may use the above results table to make a bar graph. Make one vertical bar for each metal. Under or over each bar write the name of the metal it represents. The height of the bar will show the time (minutes or seconds) it took to fill up the balloon. The shortest bar will be for the metal with the highest activity rate.


Another method of collecting data:

The only problem with the previous method is that the metal with highest activity will have the smallest bar. To correct this problem you may try a more complex method in which you measure the amount of released gas for each metal.

Fill a 25-mL or 50-mL graduated cylinder with water to the top, cover, invert, lower into a filled trough, and uncover beneath the water surface.

Place the stopper with the delivery tube (plastic tube) into the test tube. Place delivery tube into the inverted graduated cylinder.

After the setup is ready, temporarily remove the stopper, add acid to the test tube. Drop the metal piece into the test tube and immediately put back the stopper and start to take the time. Hydrogen bubbles will collect in the graduated cylinder.

After a constant period of time (such as 5 minutes) disconnect the stopper and the delivery tube at the same time.

Hold the graduated cylinder perpendicular in the water and read the bottom of the meniscus to determine the amount of water displaced by the gas.

Your new results table may look like this:

Metal name Time to fill up the balloon

If you use this table to draw a bar graph; then the metal with the highest activity rate will have the largest bar.

Materials and Equipment:

Chemicals

iron nail, wire or strips
galvanized nail or a zinc strip
copper tack or copper strip
aluminum nail or aluminum strip
6 M HCl solution (500 mL concentrated HCl solution diluted to 1.00 liter with distilled or deionized water)

Equipment

test tubes or small beakers

Modifications/Substitutions:

  1. HCl solution is available at hardware store as muriatic acid, 28% solution; this solution is approximately 8 M and may be substituted for 6 M HCl solution.
  2. Styrofoam cups or small glass jars may be used in place of test tubes or small beakers.

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.

Calculations:

No calculations is required.

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.

Some related questions that comes to my mind are:

  • If non-active metals do not react with acids, how come there are salts of such metals such as copper sulfate, Silver Nitrate and Gold Chloride?
  • Try to 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? How could this hypothesis be tested in the laboratory?

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.

  1. 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.

References:

Visit your local library and find books in inorganic chemistry. Read the chapters discussing acid/metal reactions. Also try to find a table of metals activity.

http://www.chem.pacificu.edu/Johnson/JohnsonResearch/AgonCu/intro.html

http://www.transene.com/ag.html

http://www.thomasregional.com/IMG/IMGov/0000125889/65585/65585.htm

http://www.omgi.com/industries/mintage.htm

http://swc2.hccs.edu/pahlavan/EXPERIMENT-9(1405).doc