Will The Density Of A Material Always Be The Same, Regardless Of It Size Or How Much Of It You Have?

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Lesson 3.1

What is Density?

Central Concepts

Density is a characteristic holding of a substance.
The density of a substance is the relationship between the mass of the substance and how much infinite it takes up (book).
The mass of atoms, their size, and how they are bundled make up one's mind the density of a substance.
Density equals the mass of the substance divided by its volume; D = m/five.
Objects with the same volume but different mass accept different densities.

Summary

Students will discover a copper and an aluminum cube of the aforementioned book placed on a balance. They will meet that the copper has a greater mass. Students volition try to develop an explanation, on the molecular level, for how this tin be. Students are then given cubes of dissimilar materials that all take the same volume. Students determine the density of each cube and identify the substance the cube is made from.

Objective

Students will exist able to calculate the density of different cubes and employ these values to identify the substance each cube is fabricated of. Students will be able to explicate that the size, mass, and arrangement of the atoms or molecules of a substance determines its density.

Evaluation

Download the student activity canvass, and distribute 1 per student when specified in the activity. The action sail will serve as the "Evaluate" component of each v-Due east lesson programme.

Condom

Brand certain you and your students habiliment properly fitting goggles.

Materials for Each Group

Cubes marked A–H that yous will share with other groups
Balance that can measure in grams
Calculator

Materials for the Sit-in

Copper cube and aluminum cube of the same volume
Balance

Notes about the materials

Cubes

For this lesson, you will need a ready of cubes of different materials that are all the same book. These sets of cubes are available from a variety of suppliers. Flinn Scientific sells a Density Cube Ready, Production #AP6058. This prepare comes with ten cubes—iv metal, 3 plastic, and 3 forest. Information technology is easier for students if you lot reduce the number to 8 by using all the samples of metal simply but 2 wood and two plastic cubes. Nosotros suggest using the nylon (fair, to the lowest degree dense) plastic cube and the PVC (greyness, nigh dense) plastic cube. For the woods, nosotros suggest using the oak (darker and almost dumbo) and either the pine or poplar (paler, less dense). In the activeness, each group will demand to measure out the mass of each of the eight cubes. Groups will need to measure and record their data for a cube and laissez passer it along to another group until each group has used each of the cubes.

Balances

Use a unproblematic, plastic, 2-sided residuum that looks like a see-saw for the demonstration. One of the to the lowest degree expensive is Delta Education Primary Balance (21-inch) Product #WW020-0452. Have students employ any balance that tin measure in grams.

Metric ruler

Students will use a metric ruler in the appoint portion of the action when they measure the length, width, and tiptop of a cube forth with you lot.

Most this Lesson

This is the start lesson in which students see models of molecules that are more complex than a h2o molecule. Some of these molecules may look a lilliputian intimidating. Let students know that they practise not need to memorize or draw these molecules. For the purpose of this affiliate, students only need to think well-nigh the size and mass of the atoms that make upwardly the molecule and how they are arranged in the substance.

Do a sit-in to prove that cubes of the same volume but fabricated of unlike metals have dissimilar masses.

Question to investigate

Practise cubes of exactly the aforementioned size and shape, take the same mass?

Materials for the sit-in
- Copper cube and aluminum cube of the same volume
- Balance
Procedure

Place the copper and aluminum cube on contrary sides of a simple balance.

Expected results

The copper cube will have a greater mass than the aluminum cube.
Pb a give-and-take well-nigh why the copper cube has a greater mass than the aluminum cube.

Tell students that both cubes are exactly the same size and both are solid with no hollow spots. Explicate that the aluminum cube is fabricated of only aluminum atoms and the copper cube is made of just copper atoms.

Ask students:

How can two objects, which are exactly the same size and shape, take a different mass?

Help students understand that the divergence in mass must have something to do with the atoms in each cube. There are three possible explanations well-nigh the copper and aluminum atoms in the cubes that could explain the difference in mass.
- Copper atoms might have more than mass than aluminum atoms.
- Copper atoms might be smaller and then more than tin fit in the aforementioned volume.
- Copper and aluminum atoms might be bundled differently so more than copper atoms fit in the aforementioned size cube.
Explain that any i of these explanations alone, or two or three together, could be the reason why the copper cube has more mass.

Give each student an activeness canvas.

Students will record their observations and answer questions nearly the action on the activity canvass. The Explicate It with Atoms & Molecules and Take It Farther sections of the action sheet volition either be completed equally a class, in groups, or individually, depending on your instructions. Wait at the teacher version of the activity canvass to find the questions and answers.
Project an analogy and use the pictures of the copper and aluminum atoms to introduce the concept of density.

Have students plough to the illustration of copper and aluminum cubes and their atoms on their action sheet.

Bear witness students the image Aluminum and Copper Atoms

Signal out that the copper atoms are slightly smaller than aluminum atoms. This smaller size ways that more copper atoms tin can fit in the aforementioned amount of space. So, the copper cube contains more atoms than the aluminum cube. Although they are smaller, private copper atoms actually have more mass than private aluminum atoms. The combination of more than atoms, each with a greater mass, makes a copper cube weigh more than than an aluminum cube of the same size and shape.

Explicate to students that this idea of how heavy something is compared to the amount of space it takes up is called density. The density of an object is the mass of the object compared to its book. The equation for density is: Density = mass/book or D = g/v. Each substance has its own feature density because of the size, mass, and arrangement of its atoms or molecules.
Show animations and demonstrate how to measure volume and mass of a cube.

Explain to students that volume is a mensurate of the amount of space an object takes upwards. It is e'er in three dimensions. To find the volume of an object like a cube or a box, you measure the length, width, and height and and so multiply them (5 = l × west × h). If measured in centimeters, the answer will be in cubic centimeters (cmⁱⁱⁱ).

Note: Students oftentimes confuse book and expanse. Check their understanding to make certain they know the difference. Make sure they sympathize that expanse is measured in ii dimensions (length × width) with an answer in cm². Area is a measure out of the corporeality of surface. Just book is measured in 3 dimensions (length × width × top) with an answer in cm³. Volume is a measure of the unabridged object, including the surface and all the space the object takes upwards.

Testify the blitheness Cube.

While the blitheness is playing, you lot tin demonstrate the measuring process with a cube and ruler. Have students measure forth with yous to ostend the volume of the cubes.

Volume

The cubes are two.five centimeters on each side. Show students that in gild to calculate the book, you multiply the length (ii.5 cm) × width (2.5 cm) × top (two.5 cm) to get 15.625 cm³. Rounding this number to xv.half-dozen cm³ is accurate plenty and will brand the density calculations easier. Record the volume of the cube in cubic centimeters (cm³).

Mass

Demonstrate how to use the remainder that students will be using to measure the mass of the cube. Record the mass of the cube in grams (g).

Density

Show students how to calculate density past dividing the mass by the book. Point out that the answer will be in grams per cubic centimeter (g/cm^three).

Have students calculate the density of viii different cubes and apply the characteristic property of density to correctly place them.

Student groups will not need to measure out the volume of the cubes. The book of each cube is the same, 15.six cm³, and is given in their chart on the activity sheet. They volition need to measure the mass of each of the viii dissimilar cubes and summate their densities. Students volition utilise their values for density to identify each cube.

Note: The densities students summate may non exist exactly the same as the given densities in this chart. Even so, their calculations will be close plenty that they should be able to place most of the cubes.

Question to investigate

Can you lot use density to identify eight cubes made of different materials?

Materials for the grade

Set of viii cubes of equal volume
Calculator

Teacher preparation

Use a piece of masking tape and a permanent marker to mark the eight cubes with the messages A–H.

Materials for each group

Cubes marked A–H that you volition share with other groups
Rest that can measure in grams
Calculator

Process

The book of each cube is given in the chart. It is 15.6 cm³.
Find the mass in grams of each cube using a scale or balance. Record this mass in the chart.
Merchandise cubes with other groups until you lot have measured the mass of all eight cubes.

Calculate the density using the formula D = m/5 and tape information technology in the chart.

Table 1. Book, mass, and density for unknowns A–H
Sample	Volume (cm³)	Mass (g)	Density (g/cm³)	Fabric
A	15.6
B	xv.half dozen
C	xv.6
D	fifteen.half dozen
E	15.6
F	xv.6
G	fifteen.6
H	xv.6

Table 2. Approximate densities for various materials.
Textile	Approximate density (yard/cm³)
Aluminum	2.9
Brass	8.8
Copper	9.three
Steel	viii.2
PVC	1.3
Nylon	1.two
Oak	0.7–0.9
Pine or poplar	0.iv–0.6

Compare the value you establish for density with the given value in the chart below to place which cube is made out of which cloth. Write the proper name of the fabric in your chart for cubes A–H.

Expected results: Student values for density for each cube volition not be exact, merely volition be close enough that they should be able to place each of the cubes. You may notice that the approximate densities given for each cube in this lesson are slightly unlike than those given in the cube gear up. About of this difference is probably due to the value for the volume of each cube. Since it is likely that these are 1-inch cubes, each side should be ii.54 cm. We rounded to 2.five cm because students tin can make this measurement more easily.

Hash out how the mass, size, and organisation of atoms and molecules touch the densities of metal, plastic, and wood

Explain to students that each substance has its own density because of the atoms and molecules it is made from. The metal, plastic, and wood cubes that students measured each have their own unique density. In full general, the density of metallic, plastic, and woods can be explained by looking at the size and mass of the atoms and how they are arranged.

Metallic

Project the prototype Metal

Well-nigh common metals like aluminum, copper, and fe are more dumbo than plastic or woods. The atoms that make up metals are generally heavier than the atoms in plastic and woods and they are packed closer together. The departure in density between different metals is unremarkably bsed on the size and the mass of the atoms only the arrangement of the atoms in almost metals is by and large the same.

Plastic

Project the image Plastic

Virtually plastics are less dense than metal but can accept similar density to wood. Plastics are made from individual molecules bonded together into long chains called polymers. These polymer chains are bundled and packed together to brand the plastic. One common plastic, polyethylene, is made upward of many individual molecules called ethylene which bonded together to make the long polymer chains. Like near plastics, the polymers in polyethylene are fabricated of carbon and hydrogen atoms.

The carbon and hydrogen atoms are very lite, which helps requite plastics their relatively depression density. Plastics tin have different densities considering different atoms can be attached to the carbon-hydrogen chains. The density of unlike plastics besides depends on the closeness of packing of these polymer chains.

Wood

Project the image Wood

Woods is made mostly from carbon, hydrogen, and oxygen atoms bonded together into a molecule called glucose. These glucose molecules are bonded together to form long chains called cellulose. Many cellulose molecules stacked together requite wood its construction and density.

In general, the density of wood and plastic are similar considering they are fabricated of similar atoms arranged in long chains. The difference in density is mostly based on the arrangement and packing of the polymer chains. Too, since wood is from a living thing, its density is afflicted by the structure of institute cells and other substances that brand up wood.

Ask students:

The size, mass, and arrangement of atoms affect the density of a substance.

How might these factors piece of work together to cause a substance to have a high density?

A substance with smaller more massive atoms that are close together is going to have a higher density.

How might these factors work together to cause a substance to have a depression density?

A substance with larger, lighter atoms that are farther apart is going to accept a lower density.
Have students explain on the molecular level why two blocks of dissimilar materials that take the same mass can have different densities.

Remind students that they looked at cubes that had the same volume merely dissimilar masses. Signal out that their activity canvass has drawings of two blocks (Sample A and Sample B) made of different substances that both accept the same mass, but different volumes.

Enquire students:
What is the density of Sample A?
- Book = v × 5 × 4 = 100 cm³
- Mass = 200 k
- Density = 200 one thousand/100 cm^three = 2g/cm³
What is the density of Sample B?
- Volume = 5 × 5 × 2 = l cm³
- Mass = 200 g
- Density = 200 thousand/50 cm^three = 4g/ cm³
Give two possible explanations for why one sample is more than dumbo than the other.

Hint: The size, mass, and arrangement of molecules affect the density of a substance. There are several possible answers for why sample B is more dense than sample A.
- Sample B atoms might have more than mass than Sample A atoms.
- Sample B atoms might be smaller than Sample A atoms and then more tin can fit in the same volume.
- Sample B atoms might be arranged differently so more Sample B atoms than Sample A atoms fit in the same size cube.
Whatever ane of these explanations alone, or any combination, could exist the reason why Sample B is more dense than Sample A.