September 2016 – Vol. 29 No. 1

Density Lesson

Posted: Tuesday, September 3rd, 2013

by Jeff Orlinsky

Chemistry and physical science teachers, here is a lesson on density.  It can be used with grades 10 to 12, but with some modifications it may also work with 8th or 9th grade.  This is a modification of a lab from West Catholic High School Archdiocese of Philadelphia, with references from Kenneth E. Kolb and Doris K. Kolb, Bradley University, Peoria, IL 61625 Journal of Chemical Education.

Grades: 10 – 12

Subjects: Chemistry, Earth Sciences, Physics, Physical Science, Environmental Science

Topics: Density, polymers recycling, solution preparation.

Duration: 20 min Prep + 1 hour Activity + 1 hour Post

Setting: Classroom


  • Appropriate glassware for mixing and sharing solutions
    • Seven (7) 250-mL beakers, graduated cylinders, stirring rod, long forceps
  • NaCl 90% Ethanol, 70% isopropanol, Karo syrup, monosodium phosphate, H2O
  • Different types of plastics (see below).
  • Hole punch


On TV, plastics from milk, soda and other food containers are shown recycled into park benches and plastic posts. However, for some uses the recycled plastic must all be the same type of material. Many municipalities have days when they pick up scrap metal, glass and plastics and some communities are urged to put the three types of materials in separate containers, but sometimes consumers sort the objects into the wrong category of waste. So, how is the waste accurately separated for recycling? Magnets can remove some metals from a moving conveyer belt.  Other metals and glass of various colors are sorted by hand.



And, how can the plastics be separated? Magnets cannot be used. Visual inspection, even with the aid of recycling codes, is tedious. Can density help?

This lab starts with a demonstration, allows time for students to practice with the materials and apparatus, and ends with the students designing and running an experiment to identify unknown plastics.

This table identifies different polymers and their store-bought products.


Table of different Polymers identified by densities and solution preparation


Teacher Demonstration:

  • Apparatus:  seven (7) 250-mL beakers, graduated cylinders, stirring rod, long forceps.
  • Prepare the seven (7) beakers with the different density solutions according to the chart above.
  • Demonstrate how samples of plastic sink or float in the appropriate liquids.
  • Discuss reasons why the plastics float or sink.

Guided Student Practice:

  • Apparatus: 250-mL beaker, forceps
  • Materials: distilled water, access to beakers previously used in demonstration, two (2) plastic samples (with coded identity) for each group
  • Procedure: (DONE IN GROUPS OF 4)
    • Assign two (2) different types of plastic to each pair in groups of four (4).
    • Examine the plastics and record its code and its appearance.
      • Sample Code __________________ Sample Code __________________
      • Appearance ___________________ Appearance ___________________
    • Using the solutions, observe if the plastic to floats or sinks.
    • Verify that the plastic you have floats or sinks in the correct solution.

Student Independent Practice/Lab:

  • Objective:  Each group must predict and design a way to identify the plastics using only the known density solutions.
  • Instructions for students: Plan how to use the apparatus and materials you have been assigned to identify the pieces of plastic.
  • Students have access to the beakers from the previous demonstration, plus distilled water and normal laboratory equipment.
  • Each team executes the identification plan for the pieces of plastic they have been given.
  • To add a challenge:  all known solutions must be in a single container and students cannot have 7 beakers to test all solutions.

Use of models:

  • Using words, pictures or a physical model, show how a municipality could separate the large volume of waste plastics it collects.

Written by Jeff Orlinsky

Jeff Orlinsky

Jeff Orlinsky teaches science at Warren High School and is CSTA’s High School Director.

Leave a Reply


California Science Assessment Update

Posted: Wednesday, October 12th, 2016

by Jessica Sawko

In June 2016 California submitted a waiver application to discontinue using the old CST (based on 1998 standards) and conduct two years of pilot and field tests (in spring 2017 and 2018, respectively) of the new science assessment designed to support our state’s current science standards (California Next Generation Science Standards (CA-NGSS) adopted in 2013). The waiver was requested because no student scores will be provided as a part of the pilot and field tests. The CDE received a response from the U.S. Department of Education (ED) on September 30, 2016, which provides the CDE the opportunity to resubmit a revised waiver request within 60 days. The CDE will be revising the waiver request and resubmitting as ED suggested.

At its October 2016 North/South Assessment meetings CDE confirmed that there will be no administration of the old CST in the spring of 2017. (An archive of the meeting is available at Learn More…

Written by California Science Teachers Association

California Science Teachers Association

CSTA represents science educators statewide—in every science discipline at every grade level, Kindergarten through University.

Some ways to celebrate the 100th anniversary of the National Park Service in your classroom

Posted: Thursday, September 22nd, 2016

by Carol Peterson

1) To celebrate the 100th anniversary of the National Park Service, Google has put together a collection of virtual tours combining 360-degree video, panoramic photos and expert narration. It’s called “The Hidden Worlds of the National Parks” and is accessible right from the browser. You can choose from one of five different locales, including the Kenai Fjords in Alaska and Bryce Canyon in Utah, and get a guided “tour” from a local park ranger. Each one has a few virtual vistas to explore, with documentary-style voiceovers and extra media hidden behind clickable thumbnails. Ideas are included for use in classrooms. Learn More…

Written by California Science Teachers Association

California Science Teachers Association

CSTA represents science educators statewide—in every science discipline at every grade level, Kindergarten through University.

2016 Award Recipients – Join CSTA in Honoring Their Accomplishments

Posted: Thursday, September 22nd, 2016

CSTA is pleased to announce the winners of the 2016 CSTA Awards for Distinguished Contributions, Margaret Nicholson Distinguished Service Award, 2014 and 2015 PAEMST-Science recipients from California, and the 2016 California PAEMST Finalists. The following individuals and organizations will be honored during the 2016 California Science Education Conference  on October 21- 23 in Palm Springs. This year’s group of awardees are truly outstanding. Please join us in congratulating them!

Margaret Nicholson Distinguished Service Award

John Keller

John Keller

The Margaret Nicholson Distinguished Service Award honors an individual who has made a significant contribution to science education in the state and who, through years of leadership and service, has truly made a positive impact on the quality of science teaching. This year’s recipient is John Keller, Ph.D. Dr. Keller is Associate Professor, Cal Poly San Luis Obispo and Co-Director, Center for Engineering, Science, and Mathematics Education, Cal Poly San Luis Obispo. In her letter of recommendation, SDSU science education faculty and former CSTA board member Donna Ross wrote: “He brings people together who share the desire to make a difference in the development and implementation of programs for science teaching. Examples of these projects include the Math and Science Teaching Initiative (MSTI), Noyce Scholars Program, Western Regional Noyce Initiative, and the Science Teacher and Researcher (STAR) program.” Through his work, he has had a dramatic impact on science teacher education, both preservice and in-service, in California, the region, and the country. He developed and implemented the STEM Teacher and Researcher Program which aims to produce excellent K-12 STEM teachers by providing aspiring teachers with opportunities to do authentic research while helping them translate their research experience into classroom practice. SFSU faculty member Larry Horvath said it best in his letter:“John Keller exemplifies the best aspects of a scientist, science educator, and mentor. His contributions to science education in the state of California are varied, significant, and I am sure will continue well into the future.” Learn More…

Written by California Science Teachers Association

California Science Teachers Association

CSTA represents science educators statewide—in every science discipline at every grade level, Kindergarten through University.

NGSS: Making Your Life Easier

Posted: Tuesday, September 20th, 2016

by Peter A’hearn

Wait… What?

NGSS is a big shift. Teachers need to learn new content, figure out how this whole engineering thing relates to science, and develop new unit and lesson plans. How could NGSS possibly make life easier?

The idea that NGSS could make our lives easier came to me during the California State NGSS Rollout #1 Classroom Example lesson on chromatography. I have since done this lesson with high school chemistry students and it made me think back to having my own students do chromatography. I spent lots of time preparing to make sure the experiment went well and achieved the “correct” result. I pre-prepared the solutions and organized and prepped the materials. I re-wrote and re-wrote again the procedure so there was no way a kid could get it wrong. I spent 20 minutes before the lab modeling all of the steps in class, so there was no way to do it wrong. Except that it turns out there were many. Learn More…

Powered By DT Author Box

Written by Peter AHearn

Peter AHearn

Peter A’Hearn is the K-12 science specialist in the Palm Springs Unified School District and is Region 4 Director for CSTA.

Celestial Highlights, September 2016

Posted: Tuesday, September 20th, 2016

by Robert C. Victor. Twilight sky maps by Robert D. Miller. Graph of evening planet setting times by Dr. Jeffrey L. Hunt 

Our evening twilight chart for September, depicting the sky about 40 minutes after sunset from SoCal, shows brilliant Venus remaining low, creeping from W to WSW and gaining a little altitude as the month progresses. Its close encounter within 2.5° N of Spica on Sept. 18 is best seen with binoculars to catch the star low in bright twilight. The brightest stars in the evening sky are golden Arcturus descending in the west, and blue-white Vega passing just north of overhead. Look for Altair and Deneb completing the Summer Triangle with Vega. The triangle of Mars-Saturn-Antares expands as Mars seems to hold nearly stationary in SSW as the month progresses, while Saturn and Antares slink off to the SW. Learn More…

Powered By DT Author Box

Written by Robert Victor

Robert Victor

Robert C. Victor was Staff Astronomer at Abrams Planetarium, Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs, CA. Robert is a member of CSTA.