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Whelmer #64: Liquid Rainbow
 Description:
Students are challenged to layer five liquids of different density in
a drinking straw.
Science process skills:
- observation
- classification
- measurement
- space/time relations
- interpreting data
Complex reasoning strategies:
- comparison
- classification
- abstracting
- problem solving
Standards:
K-4:
- Plan and conduct a simple investigation (Standard A.1.2).
- Employ simple equipment and tools to gather data and extend the senses
(Standard A.1.3).
- Objects have many observable properties, including size, weight, shape,
color, temperature, and the ability to react with other substances (Standard
B.1.1).
5-8:
- Design and conduct a scientific investigation (Standard A.1.2).
- A substances has characteristic properties, such as density, all of
which are independent of the amount of the sample (Standard B.1.1).
9-12:
- Design and conduct scientific investigations (Standard A.1.2).
- The physical properties of compounds reflect the nature of the interactions
among its molecules (Standard B.2.4).
Above Standards from the National
Science Education Standards.
Content topics:
- density
- solubility
You will need:
- five pitchers, milk jugs, or other large containers
- food coloring; 4 colors
- transparent drinking straws
- pickling salt
- 6 vials or test tubes for each student or group
Instructions:
Prepare five salt solutions, each with a different density. Use the following
recipe:
Pitcher #1: 1 gallon water + 0 cups of salt + bottle of yellow coloring.
Pitcher #2: 1 gallon water + 1/2 cups of salt + bottle of green coloring.
Pitcher #3: 1 gallon water + 1 cups of salt + no coloring (clear).
Pitcher #4: 1 gallon water + 1 1/2 cups of salt + bottle of red food coloring.
Pitcher #5: 1 gallon water + 2 cups of salt + bottle of blue food coloring.
Mix the solutions thoroughly, until all salt is dissolved. The solutions
must be heavily colored. Use the entire contents of one of the small bottles
usually sold in sets of four at the grocery store. Pickling salt is preferred
for this activity because it does not have any additives and will not make
cloudy solutions. Clear or translucent drinking straws must be used so that
the colors of the different solutions can be observed when in the straw.
Each student or group of students will need six small vials or test tubes;
five to hold the solutions and one to be used as a waste container.
Presentation:
Do not allow students to see how much salt is in the solutions. Do not place
the five pitchers in order, or in any other manner divulge the relative
density of the solutions.
Distribute a sample of each of the five solutions to students. Allow them
to practice placing a finger over the end of a straw and "picking up"
a sample of a solution.
Direct them to select two of the solutions at random. Draw a small portion
of the first solution into the straw. While holding the solution in the
straw, lower the end of the straw into the second liquid. Draw a sample
of the second solution into the straw. If the first solution floats on the
second, the first is less dense. If the first mixes or falls through the
second; the first is more dense.
By making comparisons of all five liquids and making record of each trial,
student will establish an order of density for the five liquids. As a extension,
challenge students to get all five solutions layered in the straw.
Content:
Analytical thinking is a skill which is important to all scientists. While
developing their own scheme to order the densities of the five solutions,
students will experience analytical thinking; perhaps, without realizing
it.
Students will also develop their own technique for drawing a small sample
of the solutions into the straw (holding their thumb over the end of the
straw, using it as a air valve). They will be challenged to determine a
technique to get all five solutions in the straw. They will learn to lower
the straw progressively lower into each solution.
Assessment:
Type: small group.
Content/Process: density.
Age/Level: all.
This Whelmer is an assessment for Whelmer #49: Potato
Float. Follow the directions for the activity. Assess students on their
accurate assessment of the relative densities of the solutions. Challenge
students to create a patriotic column...red, white, and blue...or one that
shows their school colors.
Notes:
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