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Wacky Water

Grades: 9-12
Author: Jennifer Tumlin
Source: This material is based upon work supported by the National Science Foundation under Grant No. EEC- 1542358. This lesson is inspired by teachengineering.org's Curricular Unit: Surface Tension

Abstract

The polar nature of water allows this molecule to carry out many important functions in living systems and the geochemistry of Earth. In this activity students will closely observe the behavior of water droplets to understand cohesion, adhesion, surface tension, and capillary action. Students will conduct contact angle measurements to quantify the wettability (hydrophilic, hydrophobic, or superhydrophilic nature) of surfaces. Through these investigations students will extend their understanding biomimicry and how the properties of water can be used to solve real-life problems.

Objectives

What should students know as a result of this lesson?

  • Define the following characteristics of water:
    • Adhesion
    • Cohesion
    • Capillary action
    • Surface tension
  • Describe how water’s characteristics impact living systems.
  • Describe the wettability of surfaces as hydrophilic, hydrophobic, superhydrophobic based on the contact angle.
  • Identify the factors which cause the difference in the behavior of water drops on surfaces.

What should the students be able to do as a result of this lesson?

  • Follow directions and carry out a scientific investigation.
  • Use inquiry to learn how alterations and variations of surfaces impact adhesion and cohesion of water.
  • Measure contact angle of water droplets.
  • Construct explanations based on observations.

Materials

  • Sand and aquarium gravel
  • Capillary tube demonstration apparatus (optional)
  • Waxed paper
  • Glass microscope slides
  • Disposable plastic pipettes
  • Protractors
  • Rulers
  • Digital camera for quantitative version of lab
  • Superhydrophobic leaves: Caution! Washing and touching the leaves can degrade the hydrophobic surfaces.
    • Common garden plants: iris, some milkweed, mullein, columbine, lady's mantle, many succulents, elephant ear (taro), lotus, some hosta.
    • Grocery store items: cabbage, kale, broccoli leaves (and flowers), nasturtium.

Procedures

Engagement

The teacher could wear a shirt with a comically conspicuous stain, one that students would comment on. Alternatively, just ask students what would happen if you poured a beverage or dropped your lunch on your clothing.

  • How do you know that my shirt is not stain/waterproof? (The offending substance has soaked in.)
  • What are some hints that a surface is waterproof? (Water beads up or doesn’t soak in.)
  • Are there degrees of waterproof? What happens if you dribble water down the front of your sweater, can you shake the drops off before they soak in? Why is that?

Tell students that in this lab activity they will learn about how to determine if a surface is waterproof or hydrophobic.

Show pre-lab instructions for measuring contact angle.

Exploration

Students will conduct the lab activity with a partner.

Modifications: This activity can be conducted qualitatively. Students observe the drops by eye or with hand lenses to make a qualitative sketch of the drops. They can compare the shape of the drop to those illustrated in the pre-lab powerpoint instead of calculating the contact angle.

Teacher will conduct a formative assessment of students, making sure students are properly carrying out contact angle measurements and answering questions, ideally without the help of internet search engines.

Explanation

Students will use observations and data collected during the activity to construct written, scientific explanations of the characteristics of water and surface chemistry.

Elaboration

Teacher will follow up lab with the post lab discussion powerpoint. This includes a review of the vocabulary and extension topic.

Extension discussion topics related to this can include: adaptations and natural selection, biomimicry, and engineering applications.

Extension activities could include testing commercially available coatings (Rustoleum Never Wet, car polishes, floor wax, silicone sprays, and hair cosmetics (anti-frizz and glossing serums) on glass slides, sandpaper, or Teflon tape or other materials. See images of these products and the contact angle data in the post lab powerpoint for teacher reference.

Prerequisites

  • Students should be introduced to the molecular structure of a water molecule, the polar nature of water, hydrogen bonding, and the properties of water.
  • An excellent pre-lab is the POGIL worksheet Properties of Water. (Process oriented guided inquiry learning) POGIL Activities for High School Biology. Trout, L. ed. Batavia, IL: Flinn Scientific, 2012. ISBN 978-1-933709-35-2

Best Teaching Practices

  • Questioning
  • Scientific Literacy
  • Inquiry Approaches
  • Hands On/Minds On

Alignment with Standards

NGSS Standards:

HS-PS2-6 Motion and Stability: Forces and Interactions

Communicate scientific and technical information about why the molecular-level structure is important in the functioning of designed materials.

HS-PS1-3 Matter and Its Interactions

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.

Ohio Standards:

  • Intermolecular chemical bonding. Types and strengths
  • Bonding and compounds

Biology

  • The essential functions of cells involve chemical reactions that involve water and carbohydrates, proteins, lipids and nucleic acids. A special group of proteins, enzymes, enables chemical reactions to occur within living systems.

Content Knowledge

N/A

Safety

  • Classroom safety guidelines should be followed. Students should carefully handle all glassware. Students should not eat any laboratory materials.

Applications

Having an understanding of how water interacts in the environment (gardening, cleaning, etc.) and the use of everyday products that are hydrophobic.

Engineers are taking inspiration from nature (biomimetic thinking) to solve problems in the real world.

Assessment

  • The completion of the lab worksheet is the summative assessment.

Other Considerations

Grouping Suggestions:

  • The teacher may want to require students to get a teacher check of their first contact angle photograph to verify that it is taken correctly.
  • The questions in this guided inquiry are constructed to be completed sequentially. Students should not skip questions!

Pacing/Suggested Time:

  • The lab activity could be completed in two periods or one 80 minute block.

Printable PDF Worksheets

Teacher Resources:

Student Resources:

Safety Disclaimer