Summary

In this lesson, students will investigate the properties of magic sand and learn about the concept of hydrophobic and hydrophilic molecules. It also introduces students to the field of nanotechnology.

Grade Level

Middle School

NGSS Alignment

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

• MS-PS1-1: Develop models to describe atomic composition of simple molecules and extended structures.
• MS-PS1-3: Gather and make sense of information to describe that synthetic materials come from natural resources and impact society.
• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data
  • Engaging in Argument from Evidence
• Cross-Cutting Concepts
  • Cause and Effect: Mechanism and Explanation
  • Scale, Proportion, and Quantity
  • Structure and Function

Objectives

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

• Define the terms hydrophobic and hydrophilic and explain how these properties relate to polarity.
• Collect, analyze, and graph data based on their observations of magic sand.
• Explain how shifting the properties of substances on a nano-scale can result in drastic changes of chemical and physical properties.

Chemistry Topics

This lesson supports students’ understanding of the following topics in chemistry:

• Polarity
• Matter
• Physical changes

Time

Teacher Preparation: 10-15 minutes
Lesson: 40-60 minutes

Materials

For teacher demonstration and material prep:

• Clear small aquarium or plastic container (must be see-through)
• Water
• One container of magic sand (such as is available through Educational Innovations)
• One can of Scotch Guard or other fabric protector (see teacher notes for further detail)

For each group:

• Balance
• 50 g (or more) of magic sand
• 50 g of regular sand
• 50 g of sand sprayed with Scotch Guard (“protected sand”)
• Cups and containers to hold the types of sand
• Water
• Markers (to label the cups)
• Graduated cylinder
• Paper towels (or filter paper/coffee filters)

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

• Prepare the “protected sand” samples at least a day before doing this lesson in class. For best results, spread sand out in a thin layer, spray thoroughly with Scotch Guard (or other fabric protector), and allow to dry. Then mix the sand up and spread it out again and treat with fabric protector a second time in the same way so as much of the sand as possible has been treated.
• Depending on the maturity of the students, consider reminding them not to eat the sand.
• This video provides some background information on and a demonstration of magic sand.
• To minimize distractions, keep all sand away from students until it comes time for the activity.
  • To maintain students’ attention, it may be helpful to have time set aside for them to play with the magic sand in addition to during the Engage section of the lesson.
• Clearly label all cups, or dye the Scotch Guard-covered sand to differentiate it from the magic sand and normal sand.

Lesson Overview:

Engage: Magic Sandcastle

• Before class, the teacher should create a sandcastle using the magic sand in an aquarium of water. Students should make observations and inferences based on what they see. The teacher may also allow students to reach in to touch the sand, pull it out of the water, and feel its properties. It is important that there is little background given at this stage.

Explore: Water and Sand

• Split students into groups of 3-4, or allow them to select groups if desired.
• Have students complete the prelab questions on the student handout before starting their investigation. You could have this be individual work, group work (within lab groups), or a full class discussion as you see fit. Be sure students know the correct answers to the prelab questions before completing the investigation.
• Explain that they will test how hydrophobic or hydrophilic three substances are: regular sand, sand covered with a fabric protector, and magic sand. Give students a chance to read through the procedures and ask questions and/or go over them together as a class before they obtain their materials.
  • Remind students not to tare the balance between measurements for a given type of sand, since when they tare it, the balance will subtract the mass of the cup for them, but that won’t be the case if they clear it between measurements! You could adjust the procedures so that they record the mass of the empty cup and subtract it later if you prefer.
  • You may want to instruct students on how many paper towels to use when filtering the sand to make sure they use enough that it won’t break under the weight of the sand. Filter paper/coffee filters could also be used and might be sturdier.

Explain

• Discuss with students (if needed) that water is a polar molecule, meaning that because of an unequal sharing of electrons, the molecule has a positive end and a negative end. Sand is a bit more complicated. Depending on the level of your students, you may want to simply tell them that the outside edges of a normal particle of sand are also polar, and so the sand is attracted to water molecules.
  • The more complex explanation is that sand is composed of silicon dioxide, SiO₂, which exists as a covalent network solid – there are no individual molecules or “units” of SiO₂, but rather a large, 3-D structure of interconnected Si and O atoms (see below). On the outer edges of a particle of sand, some of the oxygens bond with hydrogens to form polar –OH groups. These polar groups interact with polar water molecules, so the sand is attracted to the water.

• Question 6 in the student handout has them think about why the magic sand repels water. Once students have had a chance to think about this, explain (if desired) that magic sand is different from regular sand because it is treated on a nanoscale level to bond with a nonpolar substance, trimethylhydroxysilane (see the structure below for teacher reference). Students can simply be told that the nonpolar substance reacts with the sand to make the outside edges of the sand particles nonpolar, which means they have no imbalance of charge. This makes the magic sand particles hydrophobic and they repel water rather than being attracted to it.

Elaborate: Nanotechnology

• Depending on the reading level of students, the ChemMatters article “Magic Sand” could be given to students for further reading, or the teacher could summarize. Of particular interest might be the final section where practical applications of magic sand are discussed, including cleaning up oil spills and protecting underground electric and telephone lines in the Arctic.
  • There is also a follow-up article where student readers submitted their own ideas for practical applications of magic sand!
• Discuss where hydrophobic and hydrophilic molecules are seen in other areas of science, particularly capillary action or cell membranes. The “lotus effect” is a good example of hydrophobicity in nature, and these videos have some good background information on the science behind this effect as well as how humans have studied it to create synthetic hydrophobic materials based on the same principles.
  • Learning from Nature: The Lotus Effect – explains how scientists studied lotus leaves to create hydrophobic paint and why this is beneficial for humans.
  • Zoom Into a Louts Leaf – a video from National Informal STEM Education Network (NISENet) showing a progressively more zoomed-in view of a Lotus leaf with narration explaining why the micro- and nano-structures contribute to its super hydrophobicity.
• This is also a chance to look at other examples of nanotechnology or talk about scientific notation when dealing with nanoscale. The extension section provides students with an opportunity to think about these things further:
  • Explore the Scale of the Universe website to help students understand how small the nanoscale is. This could be done in class or outside of class for homework. (You could also point out that this awesome website was created by young students like them!)
  • Have students brainstorm practical applications of nanotechnology. The following organizations have resources that can be used to teach about nanotechnology in K–12 classrooms:
    • NanoDays Kit from NISENet
    • National Nanotechnology Initiative
    • Nanooze, a nanotechnology magazine for students
    • Frontiers for Young Minds – specifically, a nanotechnology collection
    • National Nanotechnology Coordinated Infrastructure

Evaluate

• Students have various multiple choice and open-ended questions to respond to on the student handout. These can be completed individually or in lab groups and potentially discussed as a class.
• Additional discussion prompts could include:
  • Do you think molecules can be both hydrophobic and hydrophilic? Why?
  • Watch this video on superhydrophobic coatings. How does it relate to what you have learned in class? How can this creation be used in the world?
  • Even though you coated regular sand with Scotch Guard, it still wasn’t able to repel all the water. Why might that be?
  • What do you think would happen if you mixed the magic sand with something hydrophobic, like oil? Why?