January/February 2017 – Vol. 29 No. 4

Clear Straws as Mini-Density Columns

Posted: Tuesday, January 1st, 2013

by Lisa Hegdahl

Even though I received this lab from my Master Teacher 22 years ago, I’ve never seen it presented at any conference or seminar I’ve attended.  The lab itself is a little long for a full write up here, but with the basics, you can develop an activity to suit your needs. This lab uses the skill that we all learned as kids: picking up liquids with a straw.  However, in this activity students pick up two different liquids to check relative density.  In a nutshell:

  • Prepare four solutions of different densities with varying amounts of saturated saltwater and tap water.  One container has only saturated saltwater, one container has only water, one container has half of each, and the last container has ¼ saltwater and ¾ tap water.
  • Color the liquids so they can be identified easily.  (TIP: If you use yellow and blue as two of your colors, don’t use green.  I use red, blue, yellow, and I leave one clear.)

  • Ask students to figure out the order of the relative densities of the liquids from least dense to most dense.  They do so by using their clear straw to pick up one liquid, and then a second liquid.  If the liquids stack neatly on top of each other, students know that the liquid on top is less dense than the liquid below it.  If the liquids mix, they know the liquids were not stacked in the correct order.  Those who collect data carefully should be able to layer all four liquids in their straw.
  • Students can develop their own data tables to record the results of their straw test, or teachers can create one for them.

I like this lab because the supplies are inexpensive, the activity demonstrates the intended concepts, and the students enjoy using their knowledge and investigative skills to determine the relative densities of the liquids.  I’m confident your success with this activity will be as great as mine.

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Written by Lisa Hegdahl

Lisa Hegdahl

Lisa Hegdahl is an 8th grade science teacher at McCaffrey Middle School in Galt, CA and is President for CSTA.

2 Responses

  1. Lisa, thank you for this great idea. I love that it is concise, clear and you are right, just the idea is enough to then tailor this for my own students. I’ve lifted it with a credit to you under the title. Sue (8th grade science, Orinda Intermediate School)

  2. I am definitely using this next year as an intro lesson for scientific method and problem solving. Thanks for a great problem solving exercise for my freshmen.

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