Polymer Shrinking Madness! Exploring Shrinking Properties and Chemical Makeup through Mass Spectrometry
Author: Michael Owen
Source: 1. Wayne Goates- Goddard Middle School, Goddard KS- published lesson on determination of percentage of polystyrene shrinkage. 2. Interpretation of mass spectrums and production of polystyrene and polyethylene samples of certain area with cost analysis is original.
Students will then conduct a lab activity to produce a polystyrene and polyethylene sample of a certain area after shrinking the sample in a drying oven. Cost analysis of the two shapes will be calculated. Students will also discuss mass spectrometry as an analytical technique and interpret different polymer mass spectrums.
What should students know as a result of this lesson?
- Students should know that polymers are repeating units of monomers, and are useful to everyday life.
- Students should know that mass spectrometry is an analytical technique that can determine the types of elements and bonds that are in a compound.
What should the students be able to do as a result of this lesson?
- Students should be able to design a simple experiment to create a polystyrene and polyethylene sample of a certain area after shrinking it in a drying oven.
- Students should be able to interpret a mass spectrum of a polymer and identify the molar mass of the repeating unit.
- Students should be able to conduct a cost analysis to determine the price of each shape that was produced.
- For the shrinking lab activity: Shrinkable polystyrene sheets, disposable salad containers (polyethylene), scissors, centimeter rulers, permanent markers (for decorating polymer samples), heat resistant gloves, forceps
- For the analysis of the polystyrene standard: Access to a mass spectrometer (Knight Chemical Laboratory- University of Akron) OR copies of the attached mass spectrum of polystyrene. A mass spectrum of PDMS is also attached to use during the lecture/introduction portion of the activity.
- Students will be presented with power point notes and online video clips explaining the concept of mass spectrometry and how it relates to the properties of polymers.
- Students will go on a field trip to the Knight Chemical Laboratory/University of Akron Mass Spectrometry lab (mass spectrum of polystyrene is attached if this is impractical).
Assessment: formative assessments will be made during the notes and field trip with Q and A sessions.
- Students will work in pairs in the lab to create a polystyrene and polyethylene sample of a certain area after they have shrunk in a drying oven. Students will have to test several pieces to determine the percentage of shrinkage before shrinking their final sample.
- Students will be able to observe the analysis of a polymer using the mass spectrometer OR students will interpret the polystyrene mass spectrum after reviewing a PDMS (polydimethylsiloxane) mass spectrum in class.
Assessment: formative assessments will be made in the lab while the students are experimenting with their polystyrene and polyethylene samples.
- The concept of polymers being composed of repeating monomer units will be reinforced.
- Analysis of a mass spectrum will be explained with a spectrum of PDMS (polydimethylsiloxane) and students will be taught how to determine the molar mass of the repeating monomer unit.
Assessment: formative assessments will be taken as the lab groups analyze the mass spectrum of polystyrene.
Throughout the class, mass spectrometry will be referred to as an analytical technique that can determine what elements and bonds are in a certain compound. Mass spectrometry as a technique to determine isotopic abundance and average atomic mass will also be explained and assessed on a traditional end of course exam. Summative assessments will also be made through student lab reports (rubric included on student activity page).
- Basic carbon chemistry- naming alkanes, alkenes, alkynes
- The mole concept and the calculation of molar mass
- Unit conversions (cost analysis)
Best Teaching Practices
- Hands-on, Minds-on Learning
- Conceptual Understanding of Problem Solving
- Authentic Issue Based Learning
Alignment with Standards
*Essential knowledge 1.D.2: (from AP Chemistry course description at collegeboard.org)
b. Data from mass spectrometry can also demonstrate direct evidence of different isotopes from the same element.
*HS-ETS1-3 Engineering Design (From Next Generation Science Standards)
Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.
*From Ohio’s New Learning Standards: Science-Chemistry pg 298-299
Molecules, ionic lattices and network covalent structures have different, yet predictable, properties that depend on the identity of the elements and the types of bonds formed.
Students will need to have knowledge of basic carbon chemistry and its ability to form long repeating chains. Students will also need access to the internet to confirm the formula of the polystyrene and polyethylene repeating units in order to select the correct mass spectrum. Internet access will also be necessary to do basic research into structure and uses of PDMS, polystyrene, and polyethylene.
Goggles should be worn at all times in the mass spectrometry lab when analyzing the polystyrene standard if a field trip is practical. Students should use heat resistant gloves and forceps to remove their polystyrene and polyethylene samples from the drying oven after shrinking.
Students will know that mass spectrometry is an analytical technique that can identify the types of elements and bonds in a sample. This knowledge can be applied commercially to prevent trademark infringement, or in areas of forensics. Students will also be able to relate their sample production of a certain area to manufacturing processes where definite amounts of end products are desired.
- Students will communicate their findings in their lab notebooks when explaining how they determined the percentage shrinkage of their polystyrene and polyethylene samples, and the cost to produce each sample.
- Students will be assessed on their ability to interpret a polymer’s mass spectrum on an end of unit summative assessment.
- Students should work in groups of 2 in the lab.
- Day 1: Students experiment in the lab to create their polystyrene and polyethylene sample of a certain area.
- Day 2: Lecture on organic monomers and polymers. Students explore history and general makeup of different polymer samples using online resources.
- Day 3: Students will take a field trip to the University of Akron- Knight Chemical Laboratory to visit the mass spectrometry lab and analyze a polystyrene mass spectrum (if practical). OR Day 3: Teacher will distribute copies of the attached mass spectrum of PDMS and help students to determine the molar mass of the repeating monomer unit. Students will then interpret the “mystery” mass spectrum and determine if it is the MS of polystyrene or polyethylene.
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