Core Unit: Chemicals and Reactions

1. Understand that all substances and organisms are composed of chemicals.
2. Categorize substances as pure substances or as mixtures.
3. Identify components of various types of mixtures.

1. Observe or measure some physical properties of chemical elements and compounds.
2. Demonstrate safe handling of chemicals.
3. Investigate the chemical properties of chemical compounds.
4. Design some ways to monitor the progress of chemical reactions.
5. Devise some process which makes use of the products or effects of a chemical reaction.
6. Understand how symbols and equations are used to communicate chemical information.

1. Gradually incorporate the vocabulary used to describe chemicals and reactions into written and spoken language.
2. Recognize symbols used to represent chemicals.

1. Generate, classify, and explore rules underlying categories of chemicals.
2. Propose generalizations which explain relationships.
3. Describe how patterns and regularities are useful in understanding chemicals.

Ask each student group to place a variety of substances in water and observe how they behave. Remind them to record all observations .
(Note: Always add the substances to water. Not only does this aid mixing of powders but it may be an important safety precaution. Some acids react violently when water is added to them, but when they are added to water, since they are more dense than water, they mix more easily.)

Some examples of things they might add to the water include: candle wax, steel wool, rubbing alcohol, laundry soap, vinegar, baking soda, corn starch, flour, sugar, paint thinner (use this in a well ventilated area), Alka Seltzerþ tablets, cooking oil, salt crystals, Tangþ crystals. Most of these are commonly available household substances.

Emphasize safety precautions whenever chemicals are used.

After each substance has been tested, the container used for testing should be rinsed out thoroughly before the next test. Proper disposal methods should be used for each of the substances tested. The disposal method varies, depending on the substance used. For example, the candle wax should not be poured down the drain, but can be placed in ordinary waste containers. A guide for disposal of chemicals, A Guide to Laboratory Safety and Chemical Management in School Science Activities, is available from Saskatchewan Environment and Public Safety in Regina.

Once all of the substances have been tested, students should discuss which tests might have involved a chemical reaction. A class discussion could be held as part of the follow-up to reach a consensus on those conclusions. During the discussion, students should be prepared to support their opinions, indicating what things were observed which lead them to believe that chemical changes had or had not taken place in each test.

In many cases, the difference between a chemical reaction and a physical change is not obvious. In these instances, a distinction between these two different types of phenomena need not be made.

Ensure that both girls and boys are encouraged to be involved in these activities.

Repeat, mixing egg whites and water. Shake well. Observe, record, and compare with the control. Try using egg yolks and water. Compare this with the results obtained using egg whites.

Repeat, adding some liquid detergent to an oil and water mixture. Shake and observe. Repeat again, adding egg white to the oil and water mixture. Compare all results.

The tests can be repeated using crayon, pencil, or marking pen impressions on the paper towel. For each test performed, students should observe the way the liquid interacts with the mark on the paper towel. Evidence which indicates that a chemical reaction might have occurred should be noted.

A colour change in this activity does not necessarily indicate that a chemical change has taken place. Different substances may be migrating at different rates through the paper. This is similar to what happens in paper chromatography. Dilution may also be responsible for the change in colour.

Obtain a small sample of phenolphthalein indicator. A little bit goes a long way. It can be obtained from a chemistry lab. Ex-laxþ is another source. Add Ex-lax to water and filter to obtain a phenolphthalein solution.

Use a fountain pen or pen nibs to write with the phenolphthalein solution on a sheet of paper. Allow the liquid to dry. Mist the sheet of paper with an ammonia solution from an atomizer. The indicator will turn pink in a basic solution.

Take four samples of steel wool. Soak two in alcohol. Remove the samples and allow them to dry. Place one original and one alcohol-soaked sample in separate containers of water. Repeat with the other two samples, using salt water. Label all containers. Have students predict what will happen to each sample.

Allow all samples to remain in the water for three days. Observe and compare the results. Make generalizations about the factors that contribute to the corrosion of iron.

Twin with a Secondary Level class. Arrange to have students in the senior class take slides of evidence of corrosion in the community. They can receive credit for their projects based on criteria established by their teacher at the Secondary Level. Use the slides to observe how metals corrode. Make some generalizations about things that contribute to the corrosion of metals.

Repeat, replacing epsom salts with alum. Add vinegar to the precipitate. Evaporate and compare the product to the powder produced when an alum solution is allowed to evaporate.

Hang a weighted string in the salt solutions. As evaporation occurs, top up by adding more saturated salt solution. Once the crystals have grown for several weeks, remove and dry them. Observe them carefully with a hand magnifier. Draw the shape of the crystals. Have students discuss the observations.

Add some baking soda to hot water and dissolve. Pour the mixture into an aluminum tray. Put a tarnished piece of silverware into the tray and let it stand for about an hour. Remove the silverware, rinse with tap water, and dry it. Compare it to another tarnished piece of silverware which did not receive this treatment.

Many commercial processes involve chemical reactions. Products can be purchased for cleaning copper and removing tarnish from silver. Most of these products have been developed using an understanding of chemistry. The products have important applications in our lives.

This activity takes some of the mystery out of how these products work. It also helps to show students that inexpensive alternatives can sometimes be found to replace expensive products which essentially do the same thing. This helps to develop a sense of consumer awareness to help the environment.

Pour about 30 mL of vinegar into a pop bottle. Put some baking powder in a balloon. Tap the baking powder so that it goes down to the bottom of the balloon.

Fit the opening of the balloon over the mouth of the pop bottle. Lift the balloon and shake the contents into the pop bottle. When the baking powder and the vinegar mix, a chemical reaction takes place. Gas is released. The balloon expands. Do this on a mass balance to show that mass is conserved during a chemical reaction.

Limewater (saturated calcium hydroxide solution, available from a chemistry lab) can be used to test the gas. Remove the balloon without allowing the gas to escape. Place a straw over the end of the balloon. Then place the straw in the limewater to allow the carbon dioxide gas from the balloon to mix with the limewater. Limewater turns cloudy in the presence of carbon dioxide gas.

Using a straw, exhale into the limewater. Where does the carbon dioxide in the exhaled breath come from? (Extend this into Health, discussing human respiration.)

Collect samples of chemical elements. Some should be easy to find - copper, iron, aluminum - and others more difficult. Some periodic tables have pictures of the elements. One such item is #60451 from

Boreal Laboratories
1820 Mattawa Avenue
Mississauga, ON
L4X 1K6

Have each group of students select one of the elements to research. They should try to find out: its symbol; when it was discovered; the name of the scientist who first discovered or identified it; the physical and chemical properties of the element; the uses of the element; the names of other elements that have similar chemical properties.

Groups could prepare a poster summarizing the results of their findings or report their findings in a story or poem, a song, or an interview with a group member playing the part of the element.

Have the entire class attempt to develop a classification scheme for the elements that have been investigated, based on their physical and chemical properties. Because only a small number of elements were researched, the classification extension of this activity is analogous to early attempts at classifying elements based on their periodicity.

The public nature of science is revealed through the activity. Many scientific findings have been published in a variety of resources and are available for people to use. Everyone benefits when scientific information is disclosed in this way.

Correlate this activity with the display of the table of elements at the Saskatchewan Science Centre in Regina.

Develop the connection of the symbols used and the elements they represent. Explain that some symbols are used to simplify notation. Write down the names of a few chemical compounds. Show how symbols are used to represent them. Establish that using symbols makes it easier for people to communicate in written form. To reinforce this, show how two 4-digit numbers would be expressed in Arabic and Roman numerals. (Some methods for expressing things in written form are more cumbersome to use than others.)
Write the following descriptive sentence down on the blackboard:

Magnesium metal reacts with oxygen gas to produce magnesium oxide and heat.

Write the chemical equation for this underneath the sentence:

2Mg + O2 ---> 2MgO + heat

Compare the written description of the chemical reaction with its symbolic description as a chemical equation. Note: To demonstrate this chemical reaction in class, obtain a small piece of magnesium ribbon. Hold one end of the magnesium ribbon with metal tongs. Light the free end of the ribbon. A bright flame will result. The magnesium ribbon will change to a fine white powder. Caution: This reaction produces heat. If the burning magnesium falls, it could severely burn anything it touches. Perform this demonstration over a protective mat.

Science relies heavily on the use of symbols and symbolic representations in order to convey information. Chemical and mathematical equations are common examples. Browsing through an advanced science textbook reveals the use of a wide variety of other symbols. Without the use of these symbols, communicating scientific information in written form would be very awkward and time- consuming.

Repeat a second time, using a glass of cold water and a glass of hot water. Simultaneously drop a sugar cube in each. Observe and record all changes that take place. Discuss the differences between how the sugar cube behaves in cold water and in hot water. Have students make inferences about why the sugar cube behaves differently depending on the temperature of the water.

This activity helps to reinforce ideas about how molecules behave. The rate at which the sugar cube dissolves can also be related to collisions. The average water molecule is moving more rapidly in hot water than in cold water. This allows the sugar cube to dissolve faster in hot water. The fact that water and sugar "combine" easily implies the existence of attractive forces between them.

Some students may find that recording all observations in this activity is tedious. So many different things are happening, and it is not easy to record these events descriptively. Emphasize the importance of careful recording. Certain observations should not be dismissed as being less significant than others. One never knows which observations may turn out to be the critical ones in a scientific investigation.

Working in groups, have students perform experiments in order to try to develop and test an hypothesis about what might be inside each container. The first test they do would serve to establish an hypothesis. Predictions can then be made about how the can might behave when subjected to another test. The second and any subsequent tests help to refine or replace that hypothesis, based on the new evidence. If the predictions are an accurate reflection of what takes place, then the initial hypothesis has been further substantiated.

Some examples of the types of tests that they might decide to use could be: shake the can; tip the can upside down; roll the can down an inclined plane; roll the can along the floor. Emphasize that all of the tests should be nondestructive -- that is, the containers cannot be opened or damaged when tests are performed on them.

Make sure that each group gets to test all of the numbered containers. Once this has been done, hold a "symposium," at which representatives from each group present their findings. See if consensus can be reached regarding the most likely contents of each can. Whether or not consensus is reached, have students discuss what they have learned about how investigations are carried out, and how results are shared.

Discuss the use of nondestructive observation in science. There are many examples that can be used to illustrate this. The use of exploratory techniques in medicine, such as ultrasound, x-rays, CAT scans, or fibrescopes, serve as good illustrations. Emphasize some of the reasons why the need exists for nondestructive testing.

Beneath the pendulum-magnet, place a few disk magnets in an irregular pattern on the floor. Cover those magnets with a piece of cloth or a large piece of paper.

With the students watching, swing the pendulum back and release it. Observe the motion of the pendulum. See if they can suggest what is causing the pendulum to behave erratically. If they are able to propose that other magnets under the cloth or paper might be causing the interaction, have them consider the system further to determine if similar or opposite magnetic poles are influencing the motion of the magnet.

This is an example of making inferences about unseen objects and forces from observations. Similar inferences must be made about atoms, since although we can't see them, we make assumptions about where they are and how they act based on chemical reactions.

Use the observations to make inferences about what might be different at the molecular level in the water in order to cause the drop of food colouring to diffuse more rapidly in the warm water.

A variation of this activity is to use tea bags in equal amounts of hot and cold water. Gently place the bag on the surface of each. Do not stir. Observe each for a period of about 10 minutes. Compare what happens.