Key Concepts

Density is a characteristic residential or commercial property of a substance.The density of a substance is the relationship in between the mass of the substance and how much room it takes up (volume).The fixed of atoms, their size, and also how they are arranged identify the density of a substance.Density equates to the mass of the substance split by that volume; D = m/v.Objects v the same volume yet different mass have different densities.

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Summary

Students will observe a copper and an aluminum cube that the exact same volume inserted on a balance. Castle will watch that the copper has a greater mass. College student will shot to construct an explanation, on the molecular level, for exactly how this deserve to be. Students space then offered cubes of various materials that all have actually the exact same volume. Students recognize the density of every cube and identify the problem the cube is do from.

Objective

Students will be able to calculate the thickness of various cubes and also use these values to determine the substance every cube is make of. College student will be able to explain the the size, mass, and also arrangement of the atom or molecule of a substance determines the density.

Evaluation

Download the student activity sheet, and distribute one per student once specified in the activity. The task sheet will certainly serve as the “Evaluate” ingredient of each 5-E lesson plan.

Safety

Make certain you and also your student wear effectively fitting goggles.

Materials because that Each Group

Cubes marked A–H that you will certainly share with other groupsBalance that deserve to measure in gramsCalculator

Materials for the Demonstration

Copper cube and also aluminum cube the the exact same volumeBalance

Notes about the materials

Cubes

For this lesson, friend will require a collection of cubes of various materials that space all the very same volume. These sets that cubes are accessible from a range of suppliers. Flinn scientific sells a density Cube Set, Product #AP6058. This collection comes through 10 cubes—4 metal, 3 plastic, and also 3 wood. The is less complicated for college student if you alleviate the number to 8 by using all the samples that metal yet only 2 wood and two plastic cubes. We suggest using the nylon (off-white, least dense) plastic cube and the PVC (gray, many dense) plastic cube. For the wood, we indicate using the oak (darker and also most dense) and also either the pine or poplar (paler, much less dense). In the activity, each team will should measure the mass of each of the eight cubes. Teams will should measure and also record your data for a cube and also pass it follow me to one more group till each group has provided each that the cubes.

Balances

Use a simple, plastic, two-sided balance the looks choose a see-saw because that the demonstration. Among the least expensive is Delta education and learning Primary Balance (21-inch) Product #WW020-0452. Have actually students use any balance that can measure in grams.

Metric ruler

Students will use a metric leader in the engage section of the task when they measure the length, width, and also height of a cube in addition to you.

About this Lesson

This is the very first lesson in i beg your pardon students see models of molecules that space more facility than a water molecule. Few of these molecules might look a little intimidating. Allow students understand that they carry out not should memorize or draw these molecules. Because that the purpose of this chapter, college student only should think about the size and also mass the the atoms that comprise the molecule and also how they are arranged in the substance.


Engage

Do a demonstrate to present that cubes the the same volume yet made of various metals have different masses.

Question come investigate

Do cubes of specifically the same size and also shape, have the very same mass?

Materials because that the demonstration

Copper cube and also aluminum cube of the same volumeBalance

Procedure

Place the copper and also aluminum cube on opposite sides of a basic balance.

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Expected results

The copper cube will have actually a greater mass than the aluminum cube.

Lead a discussion about why the copper cube has a greater mass 보다 the aluminum cube.

Tell students the both cubes are precisely the exact same size and also both are solid through no hole spots. Describe that the aluminum cube is do of just aluminum atoms and the copper cube is make of just copper atoms.

Ask students:

How deserve to two objects, which are specifically the exact same size and shape, have a different mass?Help students recognize that the distinction in massive must have actually something to do with the atoms in every cube. There room three feasible explanations about the copper and aluminum atoms in the cubes that can explain the distinction in mass. Copper atoms might have an ext mass 보다 aluminum atoms. Copper atoms can be smaller sized so much more can to the right in the same volume. Explore

Have students calculate the thickness of eight different cubes and use the characteristic residential or commercial property of density to correctly identify them.

Student teams will not have to measure the volume the the cubes. The volume of every cube is the same, 15.6 cm3, and also is offered in your chart top top the activity sheet. Castle will must measure the massive of each of the eight various cubes and calculate their densities. Students will use their values for density to identify each cube.

Note: The densities students calculate might not be precisely the exact same as the provided densities in this chart. However, your calculations will be close sufficient that castle should be able to identify many of the cubes.

Question to investigate

Can you use thickness to recognize eight cubes do of various materials?

Materials because that the class

Set of eight cubes of equal volumeCalculator

Teacher preparation

Use a item of masking tape and a irreversible marker to mark the eight cubes through the letters A–H.

Materials because that each group

Cubes significant A–H the you will certainly share with various other groupsBalance that have the right to measure in gramsCalculator

Procedure

The volume of each cube is provided in the chart. It is 15.6 cm3.Find the fixed in grams of every cube using a scale or balance. Document this massive in the chart. Trade cubes v other groups until you have measured the mass of all eight cubes.Calculate the thickness using the formula D = m/v and also record it in the chart.Table 1. Volume, mass, and also density for unknowns A–HSampleVolume (cm3)Mass (g)Density (g/cm3)MaterialABCDEFGH
15.6
15.6
15.6
15.6
15.6
15.6
15.6
15.6
Table 2. Approximate densities for various materials.MaterialApproximate thickness (g/cm3)AluminumBrassCopperSteelPVCNylonOakPine or poplar
2.9
8.8
9.3
8.2
1.3
1.2
0.7–0.9
0.4–0.6
Compare the value you found for thickness with the offered value in the chart below to recognize which cube is made the end of which material. Compose the name of the product in her chart because that cubes A–H.

Expected results: Student worths for thickness for each cube will certainly not be exact, however will be close enough that lock should be able to identify every of the cubes. Friend may notification that the almost right densities offered for every cube in this lesson space slightly various than those given in the cube set. Most of this difference is probably because of the worth for the volume of every cube. Because it is most likely that these space 1-inch cubes, every side must be 2.54 cm. We rounded to 2.5 cm because students deserve to make this measurement much more easily.

Extend

Have students define on the molecule level why two blocks of various materials that have actually the very same mass can have different densities.

Remind students that they looked at cubes that had actually the same volume however different masses. Allude out the their activity sheet has illustrations of two blocks (Sample A and Sample B) make of various substances that both have actually the exact same mass, but different volumes.

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Ask students:

What is the thickness of Sample A?Volume = 5 × 5 × 4 = 100 cm3Mass = 200 gDensity = 200 g/100 cm3 = 2g/cm3What is the density of Sample B?Volume = 5 × 5 × 2 = 50 cm3Mass = 200 g density = 200 g/50 cm3 = 4g/ cm3

Give two feasible explanations because that why one sample is an ext dense than the other.

Hint: The size, mass, and also arrangement that molecules influence the thickness of a substance. There are several feasible answers because that why sample B is much more dense than sample A.

Sample B atoms could have more mass than Sample A atoms. Sample B atoms could be smaller than Sample A atom so much more can right in the very same volume. Sample B atoms might be arranged differently so more Sample B atoms 보다 Sample A atoms fit in the exact same size cube.

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Any among these explanations alone, or any combination, could be the reason why Sample B is more dense than Sample A.