Introduction: (Initial Observation)
Mixing one or more substance is an important step in producing foods, detergents, paints, medicine and many other products.
For example soda manufacturers mix water, sugar, food coloring, CO2 gas and some flavor in order to produce their soda drinks. Paint manufacturers mix some glue and some pigments (color powder) in order to make paint. In making a model volcano, I mixed vinegar and baking soda. In order to make green color, I mixed yellow and blue colors. Almost in all cases, the result of such mixtures is a new product that does not look like the original ingredients. Are these chemical changes?
In this project you will investigate to determine which products are the result of a chemical change and which products are the result of a physical change?
Objectives: This project is an opportunity to learn more about chemical reactions and be able to distinguish a chemical change from a physical change.
Project Plan: Following is a list of activities that I am planning to do in this project.
Learn about the definition of chemical changes and physical changes by searching the Internet, encyclopedia and chemistry books.
Learn about methods that can be used to test physical and chemical properties of material.
Learn about separation methods if two or more substance are mixed.
Designing experiments that can be used to classify a change as a chemical change or physical change.
Adult supervision and support is required in this project
Find out about chemical changes and physical changes. Why do we need to know which is which? Read books, magazines or ask professionals who might know in order to learn about the effects of chemical change . Keep track of where you got your information from.
Following are samples of information that you may find.
Light up a candle to observe one of the most widely known chemical changes called burning.
While burning, wax from the candle and Oxygen from the air disappear and two new products are produced. These two products are Carbon Dioxide and water. This reaction also produces heat and light.
Definition: A chemical change occurs whenever compounds are formed or decomposed.reactants disappear as chemical change occurs.products appear as chemical change occurs.catalysts speed up the reaction, but aren’t produced or consumed.
Select one of the following experiments for your project:
- Reaction of Sulfuric acid and Iron
- Reaction of Silver Nitrate and Sodium Chloride
- Reaction of Hydrogen gas and Oxygen
A Physical Change is a change in state only. The original component(s) remains. (For example water may be in different states such as solid, liquid and gas. Solid water is called ice. Gas water is called water vapor. Ice, liquid water and water vapor have the same chemical composition)
A Chemical Change is a reaction occurring. A new component(s) is formed. (For example when you burn a paper, it reacts with oxygen and produces new substances including water, carbon dioxide, carbon and ash)
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 identify samples of chemical changes and physical changes. Find out what are the factors that affect the rate of a chemical change? Factors such as heat, agitation and catalyst can be studied.
The specific question that will be studied in our examples is:
How does the temperature affect the rate of a chemical change?
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.
Independent variable (manipulated variable) is the temperature. Possible values are cold, room temperature, warm and hot.
Dependent variable is the rate of reaction or the time it takes for a certain reaction to complete.
Controlled variables are agitation and wind. These are two other factors that may affect the rate of reaction.
Constants are the type and the concentration of reactants as well as experiment method and 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 for the effect of heat on the rate of chemical change.
Heat does increase the rate of chemical changes. My hypothesis is based on my gathered information and my personal observation of metal water pipes. I have noticed that hot water pipes rust and erode more than cold water pipes. Since rusting is a chemical change, then heat could possibly have something to do with higher rate of rusting.
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.”
Select the experiment of your choice from the following experiments.
Experiment 1: Reaction of Sulfuric Acid and Iron
Iron Sulfate is in the form of greenish or yellow-brown crystals and is used for water and sewage treatment, animal feed additive, fertilizer, herbicide, wood preservative and flour enrichment. To make Iron Sulfate, manufacturers simply add some diluted sulfuric acid over scrap iron. Is making iron sulfate a chemical reaction? Is iron sulfate resulted from a chemical change? In this experiment you will first observe and record the physical properties of ingredients (iron and sulfuric acid) and then compare the properties of iron sulfate with the original ingredients. Can you separate iron sulfate to iron and sulfuric acid?
(This experiment demonstrates a chemical change)
- Goggles, rubber gloves and protective clothing is required.
- Adult supervision and support are required.
- Gather about 100 grams common nails or iron filings for your experiment.
- Use a magnet to test the magnetic ability of iron.
- Obtain some sulfuric acid. Sulfuric acid 35% is available from auto part dealers as Battery fluid. Dilute your acid to about 15% to 20%. To make diluted sulfuric acid, never add water to acid, instead add acid to the water. The reason is that acid is heavier than water and it safely goes under water. Diluting sulfuric acid creates a lot of heat and hot acid is very dangerous.
- Wash the iron with warm water and detergent solution to remove any oil from the surface of iron.
- Place the washed iron pieces in a glass beaker (or any strong plastic container) and then add some diluted sulfuric acid to cover the iron pieces. Reaction must start immediately and you will see Hydrogen bubbles being released. For 100 gram iron, you will need about 175 grams sulfuric acid 100% or 875 grams sulfuric acid 20%. There are no problems if you use less sulfuric acid. If the amount of sulfuric acid is not enough, some iron will remain.
- Record the time that you start the experiment and the time that reaction stops and you see no more bubbles coming off iron pieces. The reaction may take up to a day or even more.
- Separate the green liquid and let it crystallize. Some crystals may have formed on the iron pieces. You can manually separate them. These crystals are iron sulfate.
- Can you use a magnet to separate iron from iron sulfate crystals? What happened to the hydrogen gas coming off the iron?
A few recommendations for your safety and the best result are:
- Don’t fill up your container, always keep it less than half full.
- If you are using a very strong sulfuric acid (90% or more), you may fill a beaker to 1/3rd with water, put the irons in water and then use a transfer pipette to add drops of sulfuric acid to the water.
- Always wear safety goggles and gloves and perform your experiments in a ventilated room.
Experiment 2: How does the temperature affect the rate of a chemical change (in reaction of sulfuric acid and iron)?
If temperature is able to increase the rate of chemical change, then by increasing the temperature, we should get more iron sulfate and lose more iron in a certain period of time.
Mass four identical common nails and place them in 4 different test tubes. Label the tubes as “Cold”, “Normal”, “Warm” and “Hot”.
Keep another nail outside as control. That will be a prove that loss of mass in other nails was caused by an acid reaction.
Add diluted sulfuric acid (10% up to 30%) in all tubes to cover all nails.
Place the test tube labeled “cold” in an ice water bath.
keep the test tube labeled “normal” at room temperature.
Place the test tube labeled “Warm” in a warm water bath. It can be a beaker, half filled with water, placed over a hot radiator or or any other warm heat source.
Place the test tube labeled “Hot” in a hot water bath. It can be a beaker, half filled with water, placed over a hot plate of flame of an alcohol burner.
Make initial observations and record which test tube is producing the highest amount of hydrogen gas bubbles.
After certain period of time (at least 10 hours, but you may extend it up to 24 hours or 48 hours) remove the nails one by one, wash them, dry them and record their mass. Your results table may look like this:
|Reaction Temperature||Initial mass of nail||Final mass of nail||Loss of mass||Rate of mass loss|
* Subtract final mass from initial mass to calculate the loss of mass.
* Divide loss of mass by initial mass to calculate the rate of mass loss.
You may use the above results table to draw a bar graph. Each bar represents a different reaction temperature (Cold, Normal, Warm, Hot). The height of each bar may represent the rate of mass loss. (The rate of chemical change)
Note: Instead of calculating the loss of mass in nails, you could collect, dry and mass the amount of produced iron sulfate.
Additional experiments to demonstrate physical change:
- You can mix some iron nails or iron filings with wood glue and show that the result can still be attracted to a magnet. This can be an experiment to demonstrate physical change.
- You can mix some iron filings with some wood dust and then separate wood from iron by transferring the mixture to a cup of water. Iron filings go down and wood dust stays on the surface. This is another example of physical change.
- You can mix some salt and some water. You can later evaporate the water and get the salt back. This is another example of physical change.
Additional experiments to demonstrate Chemical change:
- Mix baking soda and vinegar
- Let Iron nail rust in a test tube
- Light up a candle and show that wax from the candle and oxygen from the air are producing water. Holding a cold plate over the burning candle can condense and reveal water vapors. In this reaction, carbon dioxide gas is being produced too.
Materials and Equipment:
Iron nail can be purchased from hardware stores and sulfuric acid (also known as battery acid) from auto parts stores.
Test tubes may be purchased online or from a local scientific supplier. MiniScience.com part#TT16150_1
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.
* Subtract final mass from initial mass to calculate the loss of mass.
* Divide loss of mass by initial mass to calculate the rate of mass loss.
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.
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.
Decide if the following are chemical or physical changes.
- Frying an egg
- Vaporization of Dry ice
- Boiling water
- Burning Gasoline
- Breaking Glass
- Souring Milk
- Compression of a spring
Some more chemical changes in our daily lives:
- Examine the cupcake mix before and after it was cooked. How did it look? Did it change? The baking powder is what caused the cupcakes to rise. Is it still flour? Is is still baking powder? Is it still water? (Their response should be no.) Therefore, this is a chemical change because we have a new substance formed.
- Fill a glass 1/2 full of water and the other half with orange juice. Add 1/2 teaspoon of baking soda and 1/2 teaspoon of sugar. Is this a chemical change? (The bubbles formed carbon dioxide which was caused by a chemical reaction.)
- Observe the difference between a piece of toast and a plain slice of bread. If you scrape the brown material from the bread can you make the brown material white again? Try and see if it can be done. Since we can not do this, it is a chemical change.
- Demonstrate the procedure for making glue. Put a pint of skim milk and six tablespoons of vinegar into a glass sauce pan and heat slowly, stirring continually. When the milk forms small curds, remove it from the heat. Pour off the liquid. Dry the curds. Then add 1/4 cup of water and a level tablespoon of baking soda and stir. What did you notice? You should have noticed some bubbles. Is it still milk? Is it still baking soda? Is it still vinegar? Is it still water? Since we do not have the same materials we began with, this is called a chemical change.
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.
Visit your local library and find chemistry books that discuss the chemical change and physical changes.
Also search the Internet for “Chemical Change” to find additional information.