Time Required: 3-5 Class Periods

Physical Property: Density

Subject: Science

Grade: 4 & 6

Time Required: 3-5 Class Periods

Content TEKS and Clarifiers:
4.7 Science concepts. The student knows that matter has physical properties. The student is expected to:
(A) observe and record changes in the states of matter caused by the addition or reduction of heat; and
(B) conduct tests, compare data, and draw conclusions about physical properties of matter including states of matter, conduction, density, and buoyancy.
6.7 The student knows that substances have physical and chemical properties.
(B) classify substances by their physical properties and chemical properties
Educational Objective:
What the student must know:
Density is a physical property of substances that describes how much mass an object has per given volume. A high density substance has particles that are packed closely together. A low density substance has particles that are farther apart.
What the student must do:
Develop an operational definition for density based on experiences before calculating the density of various objects and determining the relative density of liquids.
Vocabulary:
/ Mass
Volume
Density
Irregular shape
Regular shape
NOTE: Students should be able to define vocabulary words from their learning experiences. More detailed information is found in the teacher background section.

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Grabber:

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Put vegetables into the graduated cylinder and see where they float: carrot, celery, apple, potato

ENGAGE

Prepare three black canisters for each group. One canister should be filled with cotton balls, one with rice, and the other with pennies. Fill each canister to the top so that each one contains close to the same volume. Label each container A, B, and C.
Engage students with three black film canisters and a 1000 mL beaker with water filled to the 800 mL mark.
Ask students to predict and test what is inside the container without opening it. Rules for canister testing are:

Students may not open the canisters.
Canisters may be tested by shaking.
Canisters may be tested by placing them in water.
Canister mass may be measured with a balance.
All tests and observations must be recorded in journals.

After students have had a chance to test their predictions, have them open each container to check their predictions with the actual contents and record the results in their journals.

Facilitation Questions:

Which container do you think will sink? (Answers will vary.)
Which container do you think will float? (Answers will vary.)
What is in the container that sank? (Pennies)
What is in the container that floated? (Cotton balls)
Why do you think the container floated or sank? (Answers will vary. Pennies are heavier, pennies are denser)
What would happen if you took half the pennies out of the container? (It might not sink as fast)
What other materials would you put in the container to make it sink? (Answers will vary.)

EXPLORE

Each lab group needs at least three different kinds of liquid. Each liquid should have a different density so that when they are combined in the same cup they will form layers. The best way for the teacher to insure the results is to test various liquids ahead of time, slowly pouring them into the same container to see if they form separate layers. If more than one clear liquid is used, food coloring might be added to make them visually distinct.

1. Distribute the materials to the lab groups.

2. Ask the students to predict what will happen if two liquids are slowly poured into the same cup.

3. Demonstrate the method for pouring two liquids slowly into the same cup.

4. Ask students why they think the layers remain separate, one on top of the other.

5. Challenge students to create a cup with separate layers of the same volume of liquids. Remind students to use the same volume (20 mL) of each liquid so they can compare results.

6.Ask students to find the mass of each 20 mL volume liquid sample and record in a chart in their journal.

7. The teacher may wish to display a sample of the completed density column.

Ask students to complete the Lab sheet either on paper or in their journal.

Facilitation Questions:

What property is the same for all of the samples? ( the volume)
What property is different for all of the samples? ( the mass, or possibly color)
Why did the liquids form different layers? (The liquids formed different layers because some have more mass than the others)
Where is the liquid sample with the greatest mass located in your cup? (The20 mL liquid sample with the most mass is on the bottom.)
Where is the liquid with the least mass located in your cup? (The20 mL liquid sample with the least mass is floating on the top.)
What happened to the 20 mL liquid sample that had more mass than another 20 liquid sample? (The liquid with more mass will sink below a lighter liquid.)
What happens to liquids that have less mass than another liquid? (A liquid with less mass will float on top of a liquid with greater mass.)
If you have exactly 20 mL of two different liquids and one sinks and the other floats, what can you say about the mass of the sinking liquid? (The sinking liquid must have more closely packed matter in the same volume than the other liquid, which means the same volume of liquid will have more mass.)
What happens to the particles when they have the same volume but greater mass? (The particles are packed closely together making the mass greater for the same volume.)
What happens to the particles when they have the same volume but less mass? (The particles are packed farther apart, making the mass less for the same volume.)
We can list the liquids in order, from highest to lowest density based on where they are in the column. (Answers will vary depending on the liquids used in class.)

Density

Introduction:

By comparing the behavior of different liquids, people are able to determine relative densities of the liquids. Density is a physical property that can be used to help describe different materials and substances.

Purpose:

To classify and sequence liquids based upon their physical properties.

Procedures:

Your teacher will provide you with various liquids to use.
Clean up after each step of the procedure to maintain a clean work area.
Measure equal volumes of the three liquids and place each one in a separate cup.
Measure and record the mass of each of the three sample liquids.
Pay close attention to your teacher’s demonstration of how to safely and neatly combine the liquids so they do not mix, because you will receive only one set of liquids.
Once your teacher has completed the demonstration, make a prediction of the order your three liquids will layer in the cup. Draw a picture in your journal to show your prediction.

Your challenge is to create a cup where all three liquids are clearly in order from most mass to least mass.
If your teacher allows, you may try different liquids to see how they behave.

Data:

Liquid Name / Volume (mL) / Mass (g) / Observations (What did it look like? How did it behave?)

Conclusions: (USE COMPLETE SENTENCES)

What was the sequence of your prediction from greatest to least mass?

Did your results match your prediction? What is the correct sequence of your liquids from greatest to least mass?

What did you notice about liquids that have more mass? Do they have anything in common?

Did any of the liquids combine? If so, why do you think they did that?

If you were to able to look at the really tiny molecules that make up the liquid, how will they be arranged in the liquid with the most mass compared to the liquid with the least mass? Draw a picture if it helps you explain.

Define density in your own words. What does it mean to you?

Compare your results to the class. Did your results match others in your class?

If you were to take all the liquids your teacher provided, how would they be sequenced based on the class data?

EXPLAIN

Density is a physical property that can be used from time to time to help determine one substance from another. Liquids of different densities behave differently when combined. If a liquid is denser, it will sink when carefully combined. Just as you float in the lake, less dense liquids float on top of denser liquids. When the density is high, the tiny particles are packed closer together. When the density is low, the tiny particles are farther apart. For example, water is less dense than air. The molecules in the air are much farther apart than the molecules in water.

If groups of students had different liquids, the class can make a master data table of how the liquids compare. Each group will put the order of their three liquids from least to most dense.

Group / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9
Least Dense
Most Dense

Ask student groups to sequence all of the liquids from the whole class using this data table. An example may be needed for them to understand the puzzle. For example, a portion of a data table is completed below. Notice that all three groups have water. Oil is less dense than water, corn syrup is less dense than molasses but denser than salt water, and so on. Determining he most dense substances will have to be more of an inference bases on their experiences with the substances.

Group / 1 / 2 / 3
Least Dense / Oil / Water / Water
/ Water / Salt water / Corn syrup
Most Dense / Honey / Corn syrup / Molasses

Provide students with a piece of Styrofoam and a piece of wood or a block. Ask students to look at both objects and describe them in their journals. Also have them draw what they see.
Ask students for their observations. Guide them to see the Styrofoam has loosely packed particles with pockets of air, while the block/wood does not does not have pockets of air.
Draw two rectangles of the same size (to the best of your ability) on the board. Ask students to do the same.
Have students draw circles to represent the particles in each of the objects.

StyrofoamWood/block

Point out the difference in the number of particles in each sample, even though they have the same volume.
Remind students that volume is the length times height times width.

Facilitation Questions:

Did all the liquids behave the same? (No.)
How can you identify the least dense liquid? (Least dense floats on top.)
How can you identify the densest liquid? (Most dense sinks to the bottom.)
What do you think would happen if you dropped a quarter in the liquids? (It will sink to the bottom of all the liquids.)
What is density? (The amount of mass in a given amount of space.)
What did you notice different about the Styrofoam and wood/block? (It has holes in it and the wood doesn’t. The wood is heavier, and the Styrofoam is lighter.)
How is the particle location different between the Styrofoam and wood/block? (The particles are farther apart in the Styrofoam since there are pockets of air and the wood particles are more closely packed together.)
If you had a bigger piece of Styrofoam, would the particles be located any differently? (The particles would still be packed the same, only there would be more because the piece is bigger.)
How does the closeness of the particles affect the density of the material? (The more closely packed the particles, the more dense the material.)

ELABORATE – 1 Calculating Density

Students will practice calculating the density of given objects using story problems.
Provide each student with the practice sheet and calculator, if available.
Several examples are provided to model the density calculation for the class.
Allow students adequate time to complete the other problems, assisting as needed.
Go over the questions and answers to make sure they understand the process.

Answers:

Sample 1.2 g/cm3

1.2 g/cm3
0.5 g/cm3
0.8 g/cm3
0.8 g/cm3
1.11 g/cm3

ELABORATE – 2 Calculating Density of Objects

Provide students with the materials and tools needed to calculate density, including the lab sheet.
Discuss with students the objects they will be using. Also discuss the difference between regular shaped objects (shaped in squares or rectangles that a ruler can be used to measure the volume) and irregular shaped objects (no specific shape and the displacement method should be used to find the volume).
Demonstrate the proper method of measuring the volume using a ruler. In addition, demonstrate the displacement method to find the volume of irregular solids.
Allow students to determine the densities of the objects you provided.
In addition, demonstrate that density does not change when an object is cut in half, using a bar of soap or candy bar to determine the volume and mass.
Have the students calculate the density of the demo.
Cut/break the object in half and repeat the process so students will observe that the density of the soap does not change.

Facilitation Questions:

How do you calculate the density of an object? (Divide the object’s mass by its volume.)
If you could look at the individual particles in an object, how would the particles be arranged in a very dense object compared to some object that is not very dense? (Objects that are denser have particles packed closely together. Objects that are less dense have particles spaced farther apart.)
If an object is cut in half, does the particle arrangement change? (No, the particles do not change arrangement. The mass is cut in half and the volume is cut in half also.)
If you cut an object in half, does the density change? (No, the density remains the same.)

Density of Solids

Introduction:

Density is a physical property that describes the amount of matter in a given space. In other words, it is the mass divided by the volume. When the density is high, the tiny particles are packed closer together. When the density is low, the tiny particles are farther apart. For example, water is less dense than air. The molecules in the air are much farther apart than the molecules in water.

Purpose:

To calculate the density of regular shaped solids.

Procedures:

Gather the materials provided by your teacher.
In order to determine the volume of a regular shaped solid, you must calculate the volume by taking the measurements necessary. Use the ruler and determine the volume. Record your results.

Measure the mass of the object and record your results.
Use the mass and volume to calculate the density of the object.
Repeat these steps for each regular shaped solid.

Data:

Object / Mass /

Length

(cm) / Width
(cm) / Height
(cm) / Total Volume
(cm3) / Density (g/cm3)

Not all solids are regular shaped where the volume can be measured using a ruler. Sometimes the solids are irregularly shaped and you will have to use the displacement method with a graduated cylinder to measure the volume.

Measure the mass of the object and record in the data table.
Place 30 mL of water in the graduated cylinder.
Carefully place the irregularly shaped object in the graduated cylinder without spilling or splashing any of the water out.
Record the volume of the water after placing the object in the water.
Carefully pour the water out without letting the object go down the drain.
Dry the object and return it to the materials area.
Calculate the density of the object.

Object / Mass (g) / Before Volume
(mL) / After Volume (mL) / Total Volume (mL) / Density (g/mL)

Conclusions: (USE COMPLETE SENTENCES)

Which solid has particles that are packed very closely together?
Which solid has particles that are packed more loosely?
Sequence all the solids from least dense to most dense.
If you cut one of the regular shaped objects in half, would the density change? Why or why not?
If you had two objects, one regular shaped and one irregular shaped, that were made of the exact same material, how would their densities compare?
Does the arrangement of the particles change if the shape of the material changes? Do they become more closely packed if you cut it in half?

Name: Class:

Calculating Density

Density is the measure of the amount of mass in a given volume. Water is a substance often used to compare the density to other substances and objects. If an object has a density less than 1 g/cm3, the object will float in water. If the object has a density greater than 1 g/cm3, the object will sink in water. We use a formula to calculate the density of an object. The formula for density is