Lesson

Engage

Students will be asked to explain what it means to observe. Have students provide several examples of observations that involve using their five senses. Then ask them to explain what it means to infer. Ask students to identify statements such as these to determine if they are observations or inferences;

• The metal turned red-brown on the surface because it rusted.
• The mixture turned blue.
• The solution was clear and colorless.
• The metal was hot because of friction.

Explore

Instruct students to set up a data table for recording qualitative observations over five class periods. In the table, they should record what they see, taking care to avoid drawing any conclusions from their observations. The “Day 0” observations should thoroughly describe the starting materials and the experimental setup, including approximate distances or lengths of the sections in the test tube. They could also measure the mass of the nail before they set up the experiment and after they’ve completed all their observations, but not each day. The data table may be modified by adding an additional row for quantitative observations such as the length and diameter of the nail and widths of the bands of materials in the test tube. But the key is for students to make qualitative observations and draw conclusions about whether a chemical change takes place.

1. Obtain a large test tube (25 x 150 mm).
2. Invert the test tube on a piece of filter paper and trace around the edge with a pencil. Repeat. Cut the two resulting circles from the filter paper. It is helpful to cut just inside the drawn circles as these circles will be inserted into the test tube to help keep layered materials separated.
3. Place approximately 2 cm of copper(II) sulfate in the bottom of the test tube.
4. Add a filter paper circle to the tube to cover the crystals. Use a pencil or stirring rod to position the filter paper if needed.
5. Add about 2 cm of sodium chloride as a second layer.
6. Place the other filter paper circle on top of the crystals.
7. Using a wash bottle, add a small amount of water onto the top layer to help the paper “stick” to the crystals.
8. Sand a small, iron nail with sand paper to remove any corrosion resistant coating material.
9. Gently slide the nail down the side of the test tube until it rests upon the top layer.
10. Gently add water from a wash bottle to completely cover the nail.
11. Cover the test tube with Parafilm or a rubber stopper.
12. Record all observations of appearances of starting materials and the test tube following after assembling the contents in the test tube. Note that sketches are helpful in describing some changes observed over time.

Explain

Students will create a data table that will hold their observations. Students will use their observations to identify chemical and physical changes that occur during the reaction that takes place over the course of five days. Once all observations are complete, students will then use their observations to make predictions about the materials present in the test tube.

Elaborate

Students might explore and suggest alternative materials that could be used in a similar one-tube reaction. What replacements might be possible for the copper(II) sulfate? [Students might suggest other metal sulfates or other salts such as copper(II) chloride. For other metal sulfates to work in place of copper(II) sulfate, the metal involved would have to be less reactive than iron. Lead, tin, nickel, and cobalt sulfates might work.] …the nail? [Other metals such as chromium, zinc, manganese, or magnesium could be used in place of the iron nail.]

What considerations might prevent testing of other materials? [Students might suggest safety/toxicity of some materials or the cost of materials. Other concerns include availability and cost of materials. Iron nails and copper(II) sulfate are readily available and of relatively low toxicity.]

Evaluate

• Have students compare and contrast observations and inferences, providing examples of each that are not related to this experiment.
• Have students explain the difference between chemical and physical change. [dissolving of salt and copper(II) sulfate are examples of physical change, formation of orange/brown copper metal and oxidation of the iron nail are examples of chemical change]
• Have students identify one example of chemical change and one example of physical change that occurred in the test tube.
• Ask students to explain why it is important for scientists to develop good habits of maintaining records of observations in the laboratory.
• Ask students to describe types of evidence that suggest chemical change has occurred.

Discussion Questions

Ask students…

1. What do they think the red-orange material is that develops at the bottom of the test tube?
2. What happened to the blue color over time in the test tube? Why might such a change be observed?
3. What happened to the nail over time? Where might they see something similar happen to nails over time outside of science class?
4. What subatomic particle is transferred during oxidation?
5. Describe the difference between observation and inference.
6. Why do scientists rely on observation rather than inference?

Multiple Choice Items

1. What particles are transferred between the nail and the copper(II) sulfate layers in the test tube?
   a. Protons
   b. Neutrons
   c. Positrons
   d. Electrons*
2. What type of change is evident in the tube over time?
   a. Chemical change*
   b. Physical change
   c. Loss of mass
   d. Evaporation
   e.
3. Which of the following processes explains the change in the nail?
   a. The iron in the nail was reduced.
   b. The iron in the nail was oxidized.*
   c. The salt was reduced.
   d. The copper(II) sulfate was oxidized
4. Which of the following is not an observation?
   a. The solid is red and hot to the touch.
   b. The solution is clear and colorless.
   c. The glass appears to have purple crystalline material attached.*
   d. Water is in the beaker.

Open-Ended Questions

1. What is the likely purpose of the salt layer in the reaction?
   [Examples include: separates the iron and copper(II) sulfate layers, provides a path for the movement of electrons (salt bridge)]
2. What product do you think was formed at the bottom of the test tube? Explain based on your observations and transfer of electrons in the test tube how this might be possible.
   [Since the iron nail got thinner and seemed to disintegrate, it was likely losing electrons as it “rusted” or was oxidized. These electrons seem to have been transferred to the copper(II) sulfate layer, where an orange/red-brown crystalline material formed. It is likely that the copper(II) ions were reduced to copper metal.]

Cross-Disciplinary Extensions

Connect to Math

Students could further explore the connection of the conservation of matter to the loss and gain of electrons in oxidation reduction reactions.

Connect to Reading

Have students read and write about applications of oxidation and reduction in real-life.

Connect to Writing

Students will be writing observations of change over time and will explain in writing evidence of chemical and physical change based upon observations made.

Connect to Social Studies

Disposal of war time materials, such as explosives, often involves powerful oxidation-reduction reactions. After World War I, the government disposed and excess of highly explosive sodium metal. Observe the 1947 video of sodium metal being dropped into Lake Lenore in Washington State. Explain how this disposal has impacted the lake.

Next Generation Science Standards

This lesson supports the following:

Practices of Science and Engineering

• Asking questions and defining problems
• Planning and carrying out investigations
• Constructing explanations and designing solutions

Cross-Cutting Concepts

• Patterns
• Cause and Effect: Mechanism and Explanation
• Energy and Matter: Flows, Cycles, and Conservation
• Structure and Function
• Stability and Change

Disciplinary Core Ideas, Grades 6-8

Physical science

• Substances are made from different types of atoms, which combine with one another in various ways. Atoms form molecules that range in size from two to thousands of atoms. (MS-PS1-1)
• Solids may be formed from molecules, or they may be extended structures with repeating subunits (e.g., crystals). (MS-PS1-1)
• Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it. (MS-PS1-2),(MS-PS1-3)
• Gases and liquids are made of molecules or inert atoms that are moving about relative to each other. (MS-PS1-4)
• In a liquid, the molecules are constantly in contact with others; in a gas, they are widely spaced except when they happen to collide. In a solid, atoms are closely spaced and may vibrate in position but do not change relative locations. (MS-PS1-4)
• Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. (MS-PS1-2),(MS-PS1-3),(MS-PS1-5)
• Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. The total number of each type of atom is conserved, and thus the mass does not change. Some chemical reactions release energy, others store energy. (MS-PS1-2)