Density Lab (Volume by Displacement)

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Objective

Students will be able to calculate the density of irregular shapes by determining the volume by water displacement.

Big Idea

Water displacement is used in this student lab to help calculate the density of irregular shaped objects

NGSS Background

This lesson is based on California's Middle School Integrated Model of NGSS.

MS-PS1: Matter and Its Interactions

PE: MS-PS1-2 - Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred. This lesson is specifically designed to assess the property of density of a substance.

DCI: PS1.A: Structure and Properties of Matter - Each pure substance has characteristic physical and chemical properties.

SP5: Using mathematical and computational think - the students will have to use the formula for the density formula (D=m/V) to calculate the density of different materials using their skills to weigh objects and measure the objects volume through the water displacement technique.

CCC: Patterns - density is a property of matter that can be used to identify a substance. Density is a predictable pattern in science based on the interaction of the molecules contained within any given substance. 

Students must be able to follow precise directions to measure mass and volume in order to calculate an objects density. These procedures gives the students hands-on experience using the density formula in ways that book learning never can.

This activity is designed to complement another lab called: Density Lab (Volume by Formula)

Prelab (Set-up)

25 minutes

Materials

  1. Triple beam balance scale
  2. Displacement tank (paint bucket with an inserted nozzle)
  3. Large beaker
  4. Medium beaker
  5. Small beaker
  6. Graduated cylinder
  7. Calculator

Density Samples

  1. Golf Ball
  2. Rock
  3. Scrap metal
  4. Wood block
  5. Penny stack (15 pennies superglued together)
  6. Acrylic block

Instructions

  1. Set up the Displacement tank as instructed (see directions below).
  2. Determine the mass of each sample. Place the sample on the scale and weigh it. 
  3. Determine the volume of each sample. Place the sample in the displacement tank, capture the overflow in the small beaker. Pour the water into the graduated cylindar and measure the amount of displaced water. 
  4. Divide mass by volume to determine density for each sample (D=m/V). 

Displacement Tank being calibrated for use

I have a set of cheap plastic trays that the laboratory supplies are set in for student use. This tray becomes the sink that catches any stay water. The large beaker is inverted and used as a stage to hold the displacement tank, which is then pushed to one side. The medium beaker is used to add water and the small beaker is used to catch and overflow. The graduated cylinder is used for final volume measurement.

This set-up is based upon commercial kits that sell for more money than they should. I purchased some cheap paint-mixing buckets and attached a nozzle to them for a lot less money. The items that the students use in this lab are items that I found around my house and classroom. I encourage my students, and offer extra credit, if they bring items from home. I have had students bring in toy cars, action figures, dolls, Barbie heads (didn't ask WHY), and old phones. I've even had a student calculate the volume of a working phone in a water proof case.

The tank must be calibrated before it can be used. The students pour water into the displacement tank until it starts to overflow. When the water is at the brim of the displacement tank the rig is now calibrated and ready for use. The small 'catch beaker' is then emptied and the displacement tank is ready for measurement.

Lab (Student Activity)

50 minutes

Pass out Density Lab - Volume by Displacement to every student. This packet includes instructions, data tables, and review questions in order to complete this assignment.

There are five main activities to complete this lab:

  1. Calibrate the displacement tank
  2. Measure mass
  3. Measure volume with water displacement
  4. Measure volume with a graduated cylinder
  5. Calculate density

1) Calibrating the Displacement Tank

2) Measuring Mass

3)  Measuring Volume with Water Displacement

4) Measuring Volume with a Graduated Cylinder 

5) Calculating Density (D=m/V)

 

Student Work Sample

 

 

TIP: In the past I have offered water balloons and ice balloons (frozen water balloons) as objects to calculate. The kids get a real kick finding out that ice is less dense then water. I haven't done it lately because of the added time and expense of making water balloons (45+), storing them for the lab, finding a large enough freezer, and freezing them (I'm not allowed to access to the cafeteria freezers - long story involving a frozen alligator head!). I leave the reference to the water balloons and ice balloons if I ever have extra time and energy (yeah right) to provide these objects. Thus the large X over questions 4 & 8.

Student Work Sample Questions

  1. Describe density in your own words.
  2. How can you use this method of determining volume on floating objects?
  3. Would the sample of wood have the same density as a pine tree? Explain.
  4. What was the density of the ice balloon? Why was the density close to 1 g/cm3?
  5. Will dense objects always weight more then less dense objects? Explain.
  6. How could you use the density of the rock to determine the exact material of the rock?
  7. Why could you not use the formula ‘V=lwh’ to determine the volume of each sample?
  8. What was the difference in density between the water balloon and the ice balloon? Why did they behave differently?

Extension

45 minutes

I created a Powerpoint presentation Density is mass per unit volume to teach how to calculate density.

I teach the density formula as D stands for divorce and divorce leads to a broken heart. I draw it on the board and ask the kids if they see the density formula of D=m/V.