Primary Type: Lesson Plan
Status: Published
This is a resource from CPALMS (www.cpalms.org) where all educators go for bright ideas!
Resource ID#: 126017
Rainbow Density Lab
Students make salt water solutions varying in density to create a rainbow in a 10 mL graduated cylinder. Students apply their knowledge of solutes,
solvents, solutions, and the properties of density.
Subject(s): Science
Grade Level(s): 8
Intended Audience: Educators
Instructional Time: 1 Hour(s) 30 Minute(s)
Keywords: Density Lab
Resource Collection: FCR-STEMLearn Physical Sciences
ATTACHMENTS
Rainbow Cylinder Density Lab.doc
RainbowCylinderDensityLabKEYrev.doc
Rainbow Density Quiz and Key.docx
LESSON CONTENT
Lesson Plan Template: General Lesson Plan
Learning Objectives: What should students know and be able to do as a result of this lesson?
Hypothesize how the density of a substance can be changed to create stratification (layered column)
Plan and conduct a simple investigation
Demonstrate differences in density through investigation
Create a multi-layered rainbow column using the property of density
Describe how salt changed the density of water
Prior Knowledge: What prior knowledge should students have for this lesson?
Prior knowledge will elicited by having students review relevant vocabulary terms covered earlier in the week, including mass, volume, density, buoyancy, solution,
solvent, and solute.
Students should have an understanding of density as the "concentration" of matter in a given amount of space, or mass per unit volume.
Also, students should be aware of factors that can change the density of an object such as changes in temperature and/or pressure or as in a solution by increasing
the mass (by introducing a solute) with a fixed amount of volume.
The Concept Map on page two of this resource from the University of Maine is helpful to review as a lecture topic before moving on to this lab activity. This discussion
can be conducted after reviewing vocabulary terms. Topics reviewed are buoyancy and how the layers in the ocean are created by differences in density and are
essential for currents. Salinity need not be mentioned, as student will need to investigate how changing the salinity of their solutions will affect the density.
Guiding Questions: What are the guiding questions for this lesson?
What are some factors that may affect density? (Increasing the salt concentration so that there is more mass in the same volume of solution; temperature changes
page 1 of 3 may affect density as well - the same mass in a larger volume, for example - but this will not be an observable effect with this activity since temperature is not a focus
here.)
How does the density of the ocean change with depth? (The denser parts of the ocean are deeper and the less parts of the ocean are on top. Solutions of different
densities do not mix. Cold water is denser than warm water; this plays a role in ocean currents.)
Teaching Phase: How will the teacher present the concept or skill to students?
I Do (Teacher):
The teacher will have a model lab station at his/her lab sink with all materials students will be using set up. All lab materials should be prepared before students
enter the room.
Ensure that each lab group has the following materials:
Triple-beam balance or digital scale
1 – 10 mL graduated cylinder
5 – 80 mL beakers
5 – pipettes
Sheet of paper, white
Large container filled with salt (they will determine how many grams is added to each layer and record the amounts on the data table)
Food coloring (red, yellow, and blue)
Water
Weigh trays/boats if available for massing salt
The teacher should remind students to calibrate/tare the balances before measuring the mass of their substances.
Next, the teacher reminds students that this is an guided-inquiry lab activity. Materials have been provided along with a testable question, but they must hypothesize,
identify variables, create a data chart, and collect data.
The teacher will read the question: How can you create a rainbow cylinder using the property of density?
The teacher prompts students to also take a moment to identify the test and outcome variables of this experiment.
We Do (Teacher and Students):
The teacher will circulate the room while students to write their plan as to how they will test this question to ensure hypothesis is written in an "If, then, because"
format. Also, the teacher should clarify any instructions if students have questions about them. The teacher should be sure that students have first identified density as
the variable they wish to change. The mass of salt dissolved in the water should be stated as the means by which students will change the density. The teacher should
check that students have a reasonable plan that includes the idea that changing the salt concentration (salinity) will change the density.
As students conduct the lab, the teacher will circulate around to each lab station to monitor progress, offer suggestions (if necessary), and to answer any other
questions.
You Do (Independent Practice):
After students collect data, they will work independently to analyze the data. Once students finish, the class will share their data and conclusions and review analysis
questions.
Guided Practice: What activities or exercises will the students complete with teacher guidance?
The teacher and students discuss vocabulary terms assigned prior to the lab and discuss guiding questions.
The teacher will continue to facilitate throughout the lab and review graphing instructions.
Independent Practice: What activities or exercises will students complete to reinforce the concepts and skills developed in the
lesson?
Students conduct the lab investigation to create solutions with different densities and use these solutions (after adding food coloring) to create a rainbow cylinder from
layers of different densities. Students must first determine the densities of the various solutions before attempting the rainbow column.
Students will answer analysis questions after data collection and draw an illustration of their rainbow cylinder.
Closure: How will the teacher assist students in organizing the knowledge gained in the lesson?
The teacher will review the analysis questions and clarify any questions or misconceptions students still have. Students will also take a five-question quiz to measure
whether or not the learning goals have been mastered (see Summative Assessment).
Summative Assessment
Students will submit their worksheet (see attachments for lab and key).
A quiz (see attachments for quiz and key) based on the analysis questions can be given at the end of the week or activity to ensure mastery.
Formative Assessment
Students conduct the lab activity using their prior knowledge of salinity and its affects on density to create the rainbow cylinder. The teacher measures mastery of their
understanding based on the correct layering of the different colored layers. This does depend on the order they choose, so if they choose to start with red as the
bottom and work their way to blue/violet, then red must be the most dense containing the highest concentration of salt, while blue/violet will contain no salt. If they
choose to start with blue/violet on the bottom of the column, it must be the most dense with the highest concentration of salt, and the red layer will be on the top with
no salt.
Feedback to Students
The teacher provides feedback to students on the cylinder produced in the lab and/or illustrations created by students, as well as while students are creating the
rainbow cylinder.
page 2 of 3 ACCOMMODATIONS & RECOMMENDATIONS
Accommodations:
Allow advanced students to determine the amount of salt needed to change the density of the solutions and record the amount in the data table.
For ESL students, you can review terms such as density, mass, volume, and solution, and monitor each procedure to ensure complete understanding of the
instructions. Also, you may have students use vocabulary cards and/or have visual step-by-step procedures as well.
Extensions:
Students may be provided mystery samples of liquids other than water, and based on density calculations, determine the order in which they will be layered.
Special Materials Needed:
Materials for each station (5-6 stations):
Triple-beam balance or digital scale
1 – 10 mL graduated cylinder
5 – 80 mL beakers
5 – pipettes
Sheet of paper, white
Large container filled with salt (they will determine how many grams is added to each layer and record the amounts on the data table)
Food coloring (red, yellow, and blue)
Water
Weigh trays/boats if available for massing salt
Further Recommendations:
When allowing students to create their own solutions, it may take them several trials to get each layer to the right density to make the rainbow. All lab materials need
to be set up at each station to ensure students have the most amount of time to complete data collection. This may turn into a two-day lab activity.
SOURCE AND ACCESS INFORMATION
Contributed by: Maria Jose Briones
Name of Author/Source: Maria Jose Briones
District/Organization of Contributor(s): Broward
Access Privileges: Public
License: CPALMS License - no distribution - non commercial
Related Standards
Name
SC.8.P.8.3:
Description
Explore and describe the densities of various materials through measurement of their masses and volumes.
Remarks/Examples:
Florida Standards Connections: MAFS.K12.MP.5: Use appropriate tools strategically and, MAFS.K12.MP.6: Attend to
precision.
Classify and compare substances on the basis of characteristic physical properties that can be demonstrated or
measured; for example, density, thermal or electrical conductivity, solubility, magnetic properties, melting and boiling
points, and know that these properties are independent of the amount of the sample.
SC.8.P.8.4:
Remarks/Examples:
Florida Standards Connections: MAFS.K12.MP.5: Use appropriate tools strategically and, MAFS.K12.MP.6: Attend to
precision.
page 3 of 3