Summary

In this activity, students will become familiar with the special properties of water by completing several activities that investigate the following physical properties/phenomena: cohesion, adhesion, surface tension, and capillary action.

Grade Level

Elementary School, Middle School, High School

Objectives

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

• Explain the meaning of the terms cohesion, adhesion, surface tension, and capillary action.
• Describe the unique behaviors of water molecules, and why they are important.

Chemistry Topics

This activity supports students’ understanding of:

• Physical Properties
• Properties of water
• Molecular Structure
• Polarity

Time

Teacher Preparation: 20-30 minutes

Lesson: 45 minutes

Materials (per group)

• 1 penny
• 1 dropper or disposable pipet
• 1 square of wax paper (2 x 2 inch)
• 1 watch glass
• 1 paperclip
• 1 petri dish
• 1 straw
• Water (in a small cup/beaker)

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

• At a high school level, it may be helpful if students have already learned about covalent bonds, polarity, and intermolecular forces (specifically hydrogen bonding), although you can also just introduce the concept of polarity for the purposes of this activity. At younger grade levels, students should understand that water molecules have partial positive and negative ends, or at least that water molecules are “sticky.” The properties/phenomena they will observe in this activity are a result of the attractions between the positive end of one molecule and the negative end of another. Some of the questions may need to be adjusted/deleted for younger grade levels.
• I do the prelab together as a whole group, and then let them do the activities in groups of 3-4.
• If your lab tables have their own sinks, the students can get water from the sink. If you do not have sinks at your lab table, you can provide a cup of water for each lab group.
• For Part 1, you may want to clean the pennies first. There are several ways to do this – one simple way is to soak them for 5-10 minutes in ¼ cup vinegar or lemon juice with a teaspoon of salt mixed in. (But make sure they are rinsed and dried thoroughly before completing the activity!) Alternatively, you could have different student groups compare how many drops of water will fit on a clean penny vs. a dirty penny, or give each group one of each, or compare heads vs. tails.
• For Part 2, it does not have to be a watch glass necessarily – any glass surface will do. For example, you could use a microscope slide, or turn a glass beaker upside down and use the bottom of the beaker. In any case, you should see the edges of the water droplet attract more to the glass surface, in effect flattening out the droplet a bit compared to the rounder water droplet on the wax paper, which has less attraction to the surface (adhesion).
• For Part 3, it may be helpful to bend one end of the paperclip up to use as a sort of handle to help with setting it down carefully onto the water. If students are familiar with the concept of density, they may think it floats because it is less dense than water. You can show that this is not the case by submerging the paper clip so that it sinks.
• For Part 4, use a clear straw so that they can see the water rise up the straw. You could have students compare different width straws – water will reach a higher level in smaller diameter straws than in wider ones!
• There are many possible extensions you can do for this activity! There is one listed for each of the four parts at the end of the student document. You could also do any/all of this activity again with different liquids (soapy water, salt water, isopropyl alcohol, acetone, cooking oils, etc.) or surfaces, conduct a thin layer chromatography demo/lab for capillary action, research real world applications/phenomena that depend on surface tension or capillary action, etc.
• There are so many resources out there for studying water! Here are some good ones you could use to further teach about the properties of water:
• AACT Lab: Abe Goes Swimming
• AACT Demo: Analyzing Mixtures
• AACT Demo: Intermolecular Forces & Physical Properties
• Middle School Chemistry, Chapter 5: The Water Molecule and Dissolving
• The USGS Water Science School, Water Properties