Introduction: (Initial Observation)
We have seen rusted iron that is a red/brown powder and has none of the properties of the original iron any more. Iron rusts when it is exposed to air and moisture. Rusting iron is a chemical change that is happening around us every day. But there is another chemical change that we are causing every second. We inhale oxygen and exhale carbon dioxide. This is a chemical change that happens in our lungs. Produced carbon dioxide has none of the properties of carbon or oxygen and can not be converted back to carbon and oxygen by physical methods such as filtration.
Actually millions of chemicals in the world are made by a chemical change; exceptions are just a few chemicals that can be found pure in the nature. Most medicines, most fabrics and all plastics and most metals are made by chemical change.
This simply means that for your chemical change project, you have millions of experiments to choose from. Your project can be as simple as burning a piece of wood or paper. You like to work more advanced? rusting iron, electrolysis of salt, reaction of acids and alkalis are all possible experiments that you can work on.
Information Gathering:
Find out about chemical change. Read books, magazines or ask professionals who might know in order to learn about the causes of chemical change. Keep track of where you got your information from.
A chemical change is a change in which one or more new substances with new properties is formed. When paper is burned, the ashes formed are entirely different from the original paper that was burned.
A property is a set of identifying characteristics about a substance. Physical properties are easy to identify because they involve your senses of sight, touch, taste, smell and hear. Common examples of physical properties include the color, size and texture of an object. The characteristics, however, are not enough to identify a material. Additional ones such as density, and freezing point are needed.
Any slight change in these physical properties brings about physical changes such as when ice melts. The substance changes size, shape or state, but does not change into a new substance with new properties. One of the most common examples of a physical change is the melting of ice. Ice is solid H20; when it melts, it becomes liquid H20.
Chemical properties are those properties a substance possesses because of its action or lack of action with other substances. Reaction with an acid, or reaction with oxygen (combustion) are just a couple of examples of chemical properties.
Studying chemical properties is usually done when chemical changes are observed.
Chemical and physical properties and changes are characteristic of every substance. See if you can identify the following as physical or chemical by creating a chart and marking each example under the proper category:
1. tearing a piece of paper (Physical)
2. burning wood (Chemical)
3. a candle 5 inches long (Physical)
4. boiling water (Physical)
5. adding hydrochloric acid to zinc (Chemical)
ACTIVITIES:
1. Dissolve a small amount of salt in water. Is this a chemical change or a physical change? (Physical) Allow the solution to evaporate. Is this a chemical or physical change? (physical)
2. Add a small piece of zinc to 5 ml of hydrochloric acid. Is the reaction a chemical or physical change? (Chemical) (This activity is ONLY for higher grades students with access to a chemistry lab and a chemist)
3. Burn a small piece of Mg ribbon by holding it with tongs in a flame until it catches fire. Do not observe directly. Is the change a chemical or physical one? (Chemical)
4. Put a small nail into a bottle of Coke and leave it for one week. Is the change a chemical or physical one? (Chemical)
5. Light a candle and allow it to burn five minutes. Extinguish. Is the change in the candle physical or chemical? (Physical)
There are different types of chemical change, following is a list and some examples.
| Type | Definition | Examples |
| synthesis | a compound forms from simpler reactants | C2H4(g) + H2O(g) =>C2H5OH(g) H2(g) + ½ O2(g) =>H2O(l) |
| decomposition | a compound breaks down into simpler products | CaCO3(s)=>CaO(s) + CO2(g) 2NH4NO3(s)=>2N2(g) + 4H2O(g) + O2(g) 2 H2O(l) =>2 H2(g) + O2(g) |
| displacement | Zn(s) + 2 HCl(aq)=>ZnCl2(aq) + H2(g) Zn(s) + CuCl2(aq)=>ZnCl2(aq) + Cu(s) |
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| neutralization | H+ transfer from acid to base | NaOH(aq) + HCl(aq)=> H2O(l) + NaCl(aq) KOH + HC2H3O2(aq) =>H2O(l) + KC2H3O2(aq) |
| precipitation | a solid product from aqueous reactants | BaCl2(aq) + Na2SO4(aq) => BaSO4(s) + 2 NaCl(aq) AgNO3(aq) + NaCl(aq) => AgCl(s) + NaNO3(aq) |
| redox | electron transfer between reactants | 2 C2H6(g) + 7 O2(g)=> 4 CO2(g) + 6 H2O(g) |
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 project is to demonstrate chemical change caused by chemical reactions. A possible question related to this demonstration is what material will rust in the air (react with the air in room temperature)?
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.
For the demonstration purpose, you don’t need to identify any variables. In future you might be doing research on a specific chemical reaction. Then you may need to identify variables. For example you may be researching on factors affecting the rate of rusting in iron. Then each factor that you study will be one variable. So if you are studying on the effect of temperature on rusting iron, then temperature is a variable.
For the question about material that rust, the type of material is a manipulated variable. (manipulated or independent variable means the variables that you change in order to to see some effects). The result (rust or no rust) is the dependent variable. (means that rusting depends on the type of material)
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.
Among my test samples that include glass, iron, plastic, aluminum and wood, I think only iron will rust.
Experiment Design:
Here we discuss different experiments for different methods of chemical change. You will select only one of these experiments for your project.
Experiment 1: Rusting Experiment:
In this experiment you test different material to see which one will rust in the air and in presence of moisture.
Procedure:
Get a few plastic or glass cups and label them with the name of material that you are going to test. Inside each cup place a sample of the material. For Iron, you can use a few iron nails. Make sure they are all clean and have no rust or grease on them. You may need to wash the nails with soap and warm water before your experiment. For aluminum, you may cut pieces from aluminum foils or aluminum disposable containers. Don’t forget washing. For plastic, use a broken plastic toy or plastic spoon. For wood, use any piece of wood. A short wood dowel can be fine.
Think about any other material that you may want to test. Copper, gold, silver, glass, paper, cotton and stone are among the material that you can test.
Place a few pieces of each material in a cup and spray them with tap water about 4 times a day. (So you need to have a spray bottle too.) It is good if a small amount of water remains in each cup, so the moisture will remain in the cup. You may also cover all cups with a piece of paper.
After 2 weeks, visually inspect all the material that you are testing. Do you see any change. Is any of the material covered with a layer of another new substance?
Check the color of water remained at the bottom of each cup. Do you see any change in the color of the water?
Record your observations in your reports. Use the results of your experiment to decide which material caused a chemical change in air, while moisture is present.
Use your experiment setup as a part of your display.
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Experiment 2: Chemical change caused by burning:
Turn on a candle, hold a cold glass cup above that for a few seconds, you will notice water drops or steam will condense inside the glass.
Where does the water come from?
Hydrogen atoms from the candle wax will react with oxygen from the air and create water. Maybe that is why they call it “Hydro-gen”, because water is generated by its combustion. (Hydro means water). Candle wax is a long chain of carbon atoms with 2 hydrogen attached to each carbon. While candle burns and it’s hydrogens produces water, it’s carbons also produce carbon dioxide. In the following image we display Carbon atoms by black circle, Hydrogen atoms by blue circle and Oxygen atoms by red circle.
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Experiment 3:Chemical change caused by an electric current:
Chemical change caused by an electric current is called electrolysis. Here we try the most commonly known electrolysis experiment that is water electrolysis. In this experiment we use a 12 volts direct electric current from a battery to electrolysis water and produce hydrogen and oxygen.
You can simply connect two wires to the negative and positive poles of a battery and insert the other end of these wires in a cup of water. You will soon see hydrogen bubbles forming around the negative wire and oxygen bubbles forming around positive wire.
There are a few problems though. One is that the process is very slow because pure water is not a good conductive. This can be fixed by adding some electrolyte to the water. A few drops of sulfuric acid can be the answer to this problem. Sulfuric acid is a good electrolyte. The other problem is that your water will become dirty very soon. The reason is that oxygen will also oxidize your positive wire and metal oxides enter the water. If you are using sulfuric acid as an electrolyte and your wires are copper, then you will have copper sulfate in the water. To prevent this problem, use graphite as the electrode. In other words, you connect a piece of graphite rod to your wires and insert the graphite in to the water. So your wire does not get wet. Graphite is conductive, like metals, but does not enter any chemical reaction with oxygen or sulfuric acid. In this way your water will remain clear.
Now it is good if you can collect the produced hydrogen and oxygen in two different container.
To do this make two holes at the bottom of a plastic container. Pass one graphite bar from each hole and seal the holes with a water resistance glue such as hot melt glue or epoxy glue. At this time one end of each graphite bar is inside the container and the other end is outside.
Fill up the container with enough water to cover the graphite bars. Also fill up two test tubes with water, turn them up-side down while covering their top with your finger (or a small piece of paper) and place them upside town over the graphite bars. If you do it right, your test tubes must still be filled with water.
Now you can connect the other end of graphite bars that is outside the container to the poles of a 12 volts battery. The process of electrolysis will start immediately and water molecules will start to break down to hydrogen and oxygen. If the process is slow, add a few drops of sulfuric acid to your water.
Sulfuric acid is used in car batteries and may be purchased from auto-parts store. It is strongly corrosive and when concentrated, can hurt your skin and small drops of that makes holes on your clothes.
To be safe, you can dissolve use a very small amount of copper sulfate in water and add that instead of sulfuric acid. Copper sulfate will be sold at places who sell pull supplies.
Higher grade students who need to do an experimental project related to chemical change, may require to have a question, propose a hypothesis and define variables. These are two sample questions:
Does voltage affect the rate of oxygen and hydrogen production in water hydrolysis?
Does temperature affect the rate of rusting?
Experiment 4: Does voltage affect the rate of oxygen and hydrogen production in water hydrolysis?
Repeat experiment 3 with 3 different voltages (3 Volts, 6 Volts, and 9 volts).
Measure and record the amount of Oxygen gas produced every hour with different voltages. If your apparatus is small and you have to terminate your experiment in less than one hour, then you must do some calculations to calculate the oxygen production per hour. For example if your apparatus makes 7 ml oxygen in 5 minutes, then you can multiply 7 by 12 in order to calculate the hourly production of oxygen. (The number of 5-minutes in each hour is 12)
Your results table may look like this:
| Electrolysis Voltage | Milliliters of oxygen produced each hour |
| 3 | |
| 6 | |
| 9 |
Make a graph:
Use a bar graph to visually present your results. Make one vertical bar for each of the voltages you test and name the bars accordingly. The height of each bar will show the hourly production of oxygen with that specific voltage.
Materials and Equipment:
List of material can be extracted from the experiment section.
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 calculation is required for this project.
Summery 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:
Visit your local library and review some chemistry books (introductory level). See if you can find samples of chemical change reactions.
