• During the guided instruction portion of the lab, listen carefully to student responses as they brainstorm potential physical properties. Guide students to use everyday experience with water to form proper conclusions regarding water’s properties.

• The Physical Properties Lab provides an opportunity to assess students’ understanding of the guided instruction. During the lab, rotate between student teams and use the following questions as a guide in determining student understanding:

• “You determined the mass and volume of Unknown 1. Do you think mass and volume are physical properties? Why or why not?”

• “If you increased the amount of Unknown 1, would the density change? Why or why not?”

• “If you were to smell Unknown 2, is that a function of how well it evaporates? Why or why not?”

• “What are some other physical property tests you could perform to aid in identifying the unknowns?”

Fill a large glass with water even to the rim. Ask students, “Is this glass of water full? How many paper clips do you think I could add to this glass of water, before the water overflows?” Students will see that you can add many more paper clips to the glass than they thought.

Follow this demonstration with another quick example:

1. Give a penny, pipette, and a small jar of water to every fourth student.

2. Have groups of four (at their desks) first estimate how many drops of water the surface of the penny will hold before the water spills over the sides, and then perform the experiment.

3. Have students place the penny on the desk and begin to place as many drops of water as they can on the coin until water runs off the surface of the penny.

For an extension, students could try this same demonstration with isopropyl alcohol or an alkane, such as hexane, instead of water.

Part 1

Ask students, “Why do you think you can add several more paper clips to the already full glass of water? Why could you add more drops of water to the penny than you could with alcohol or hexane?” Let students make educated guesses. Some may offer answers such as, the water is denser or it sticks together more. Tell them, “All of the substances that we looked have unique physical properties. The physical property you just explored is called surface tension, which allowed the water molecules to cling to the side of the glass and the penny.”

Let this answer guide you into a discussion of physical properties. Put the definition of physical properties on the board, overhead or interactive white board. Working with water, ask students to brainstorm other physical properties of water. On the board, make a list of their answers. When you feel that they have exhausted their guesses, circle the ones that are correct and then add properties that were not yet guessed. Define each. Below is a list of some physical properties. You may add to or remove from the list any properties you want.

• Viscosity: Viscosity describes a liquid’s resistance to flow. Greater resistance is higher viscosity.

• Density: Density is a physical property that describes how much mass is in a specific volume. D = m/v.

• Conductivity: Describes how well something conducts electricity.

• Magnetism: Describes how matter responds to a magnetic field.

• Boiling/Melting/Freezing Point: The temperature at which a substance boils/melts/freezes.

• Thermal Expansion/Contraction: Describes the change in volume as a substance is heated or cooled.

• Malleability: How easily a substance can be molded, bent, and shaped.

• Ductility: the extent to which a material can be deformed plastically without fracturing.

• Surface Tension: The cohesive forces between liquid molecules.

• Volatility: A measure of the tendency of a substance to evaporate.

Part 2

Demonstrate some of water’s physical properties.

Demonstration 1(Boiling Point)

Set up a distillation apparatus on the front counter. Add tap water and food coloring to the round bottom flask. Let the water distill for a few minutes. Explain that distillation “is a method of physically separating a mixture based on the boiling points of the components in the mixture. The mixture is made from water and food coloring. Water has a specific boiling point (at a given pressure), which is 100ºC. Food coloring has a higher boiling point than water. You will see the water boil first, vaporize into a gas, and then condense back into liquid water (because of the cool water running around the outermost channel). Eventually, you will be left with just dye in the round bottom flask and pure water in the beaker.” If you do not have access to a distillation apparatus, you can show students a distillation animation, such as this one: http://www.saskschools.ca/curr_content/science10/unita/redon18.html

Demonstration 2 (Thermal Contraction/Expansion)

Ask students, “Has anyone left a can of soda in the freezer or in a cold car too long?” Most students have had experience with this and will acknowledge that the can exploded. Then ask, “Of what is soda mainly made?” Students might say sugar, bubbles, and water. Focus on water, which is over 90% of soda’s volume. “Soda is mainly water, which, unlike most liquids, expands when it freezes! This is a physical property of water, called thermal expansion.”

If you have access to liquid nitrogen, you could fill a balloon with helium and place it in the liquid nitrogen to see that helium contracts when it is cooled, unlike water. If you do not have access to liquid nitrogen, you could demonstrate the same thing by placing the balloon in the freezer for about an hour.

Demonstration 3 (Density)

Introduce this next physical property with a glass of ice water sitting on the front table. Ask students what they notice about the glass. Lead them to thinking about why the ice cubes are floating on the liquid water. Remind them that the solid ice and liquid water are the same thing, just in different states. Explain, “Solid water is less dense than liquid water. As water freezes, it expands, creating more volume. Since density is a function of volume, solid water is less dense. Less dense substances will float!” Do a follow up demonstration using isopropyl alcohol (rubbing alcohol). Fill a graduated cylinder with the alcohol and place ice cubes in the cylinder. The ice will sink because it has a greater density than isopropyl alcohol.

In a clear tank (an empty aquarium would work) place several liters of water. In front of students, place a can of cola and a can of diet cola into the tank. Explain, “There is considerably more mass per unit volume in the regular cola than the diet cola, causing it to be denser and sink.”

Demonstration 4 (Conductivity)

Place a sample of distilled water that you purchased from the store (or use the distilled water from Demonstration 1) in a beaker. Use a conductivity set with a light bulb to show that distilled water is a poor conductor of electricity. Do the same with salt water, which will be a better conductor.

Demonstration 5 (Viscosity)

Pour a small amount of honey from a high height (so students can see) into a jar. Do the same with water. Ask, “which substance has a higher viscosity, remembering that viscosity is resistance to flow?”

Lab Activity

Use the Physical Properties Lab–Teacher Version sheet (S-8-5-1_Physical Properties Lab Teacher Version.doc) to set up the Physical Properties lab and to correct and assess students’ work when they have finished the lab. Assign students to teams. Hand out Physical Properties Lab–Student Version (S-8-5-1_Physical Properties Lab Student Version.doc) to students. In their groups, they should complete the information tables on the unknown substances and answer the analysis questions.

Extension:

• For students performing above and beyond the standards, consider discussing fractional distillation, used in the petroleum industry. For details and an animation of this process, go to: http://www.howstuffworks.com/oil-refining4.htm

• If you have access to dry ice (CO₂), you can place about 3 cups of it in an aquarium. Let it sublimate for 10 to 15 minutes. Light a candle. Take a beaker and “scoop” out some of the CO₂ vapor. It will look to students as if you are not removing anything. Quickly pour the vapor over the burning candle. The flame will extinguish due to the density of CO₂. Relate this to fire extinguishers.