Summary

In this lab, students will design a procedure to test and compare the water resistance ability of several unidentified fabric samples. Students will then attempt to identify each of the unknown fabric samples by analyzing the polarity of each molecular structure in combination with the data collected in their test.  

Grade Level

High School

NGSS Alignment

This lab will help prepare your students to meet the performance expectations in the following standards:

• HS-PS1-3: Plan and conduct an investigation to gather evidence to compare the structure of substances at the bulk scale to infer the strength of electrical forces between particles
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Planning and Carrying Out Investigations
  • Constructing Explanations and Designing Solutions
  • Engaging in Argument from Evidence
• Cross-Cutting Concepts:
  • Patterns
  • Structure and Function

Objectives

By the end of this lab, students should be able to:

• Interpret a molecular structure to determine polarity.
• Explain how polarity of a molecule that makes up a fabric affects water resistance.

Chemistry Topics

This lab supports students’ understanding of:

• Polarity
• Intermolecular Forces
• Molecular Structure
• Hydrophobic and Hydrophilic Molecules
• Identification of an Unknown

Time

Teacher Preparation: 30 minutes
Lesson: ~1 hour

Materials

• Clothing samples or fabric swatches made of:
  • Polyester
  • Cotton
  • Nylon
  • Rayon
  • Others (optional)
• Spray bottles filled with water

Safety

• No safety considerations for this activity.

Teacher Notes

• This lesson was created for the 2022 National Chemistry Week celebration: Fabulous Fibers: The Chemistry of Fabrics

Background:

• A water-resistant fabric will dry quickly because it doesn’t absorb moisture well.  The molecules that make up the fabric determine water resistance. If the molecules are nonpolar, the fabric will be water-resistant. Nonpolar molecules are hydrophobic, meaning they repel water. This concept is the basis of the activity.
• A lot of water-resistant clothing materials are made of a combination of different fabric types (for example, a pair of leggings that is 60% polyester and 40% cotton) to make them breathable as well. This allows the fabric to have multiple properties—such as limiting water absorption while also allowing sweat to escape.
• Polyester as a material, for example, is hydrophobic and is very water resistant. But, because of this, it doesn’t allow sweat to escape very well. You can find polyester used in rain jackets, as well as water bottles, sails, and insulation.

Teacher Preparation:

• Obtain four (or more) articles of clothing or fabric swatches made of different materials (nylon, polyester, rayon, cotton, etc.). If possible, cut the fabric into 10cm x 10cm squares. You will need enough squares for each student group to have their own samples.
• Consider visiting a thrift store or asking for donations from students for the activity. Alternatively, fabric by the yard can be purchased at a craft store.
• If the fabric samples are each a different color, it would be helpful in keeping track of the identity of each sample. If not, teachers should label the fabric samples with numbers. Be sure that students are not told the type of each sample of fabric, since they will be using critical thinking skills to identify each fabric type based on data collected in combination with its molecular structure.

Activity Overview:

• This activity will begin with a discussion. Ask students to share ideas about clothes they might wear during rainy or snowy weather and compile their responses on the student worksheet. They may suggest items such as raincoats, snow boots, and hats.
• Ask students how they could test whether a certain piece of fabric would be suitable for rainy or snowy weather and again compile their ideas on the student worksheet.
• In the pre-lab students are tasked with determining the polarity of the four molecules that make up the fabrics used in the activity. Help guide students to first make basic observations about the structures if they are overwhelmed—they probably are not used to molecules this big. Students should determine polarity, with teacher assistance as needed.
  • Teachers can build 3-D models of the molecules if you have the kit available (optional).

• Note that if different fabric types are used then the student handout should be updated to reflect the change. Currently the student handout is designed for cotton, nylon, rayon and polyester.
• Reviewing the polarity of each molecule as a class might be beneficial since the structures are much bigger than a typical structure chemistry students might encounter. Students may need guidance visualizing symmetry/opposite dipoles. Also helping students draw the carbon atoms in the structure can be helpful for their understanding.
• Students will then design a procedure with their lab group (3-4 students recommended) to test the water resistance of the different fabric samples.
  • Show the materials that are available for testing.
  • As groups develop a plan, remind them that their procedure should include variables that stay constant, such as amount of water to be sprayed on each piece of clothing, etc.
  • They may decide to record data such as how wet the fabric sample feels, the appearance of the fabric sample, how long it takes the fabric sample to feel dry, etc.
  • If your class meetings are short make sure students are testing with very small quantities of water so they don’t run out of time.
  • Encourage students to include multiple points of data collection (ex: 0 minutes, 5 minutes, etc.)

• For the investigation each group will receive 4 unknown samples of fabrics. Students will follow the procedures that their group designed to investigate water resistance.
• After the investigation, it might be helpful to ask students how chemistry could prevent water from being absorbed by clothes. A few students will probably bring up the word hydrophobic. You can explain that nonpolar molecules are hydrophobic, or based on the level of understanding by students you may or may not want to direct them to this connection right away.
• Students will then need to evaluate their pre-lab assignment and compare it with the data collected from testing to attempt to identify each fabric sample. Note that they will need to justify their answer for each identification.
• An Answer Key document has been provided for teacher reference.
• Note that the molecular structures used in the student handout are from the following sources:
  • Cotton: ChemMatters Magazine, October 2022. Used with permission.
  • Nylon: ChemMatters Magazine, October 2022. Used with permission.
  • Polyester: Wikimedia Commons, attribution: Schippmeister
  • Rayon: Wikimedia Commons, attribution: Berserker79
• As an extension activity, consider having your students read either:
  • “How to Sweat and Not Stay Wet” article from the ACS 2022 National Chemistry Week magazine, Celebrating Chemistry.
  • “Don’t Sweat It: How Moisture-Wicking Fabrics Keep You Cool and Dry” article from the October 2022 issue of ChemMatters Magazine.