Lesson

Engage

Before class, the teacher should create a sand castle 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

1. Explain to students the difference between hydrophobic and hydrophilic substances. Use the Latin prefixes and suffixes to help (hydro-, -philic, -phobic)
2. Ask students: Is the sand in the aquarium hydrophobic or hydrophilic? Why? [hydrophobic, it repels water]
3. Ask students: What are some other examples of hydrophobic substances? [coating of rain jackets, oil]
4. Tell students that they will test how hydrophobic or hydrophilic three substances are—regular sand, sand covered with a fabric protector, and magic sand
5. Split students into groups of 3–4 and have each group obtain the materials above.
6. Have students label the cups Regular Sand, Protected Sand, and Magic Sand.
7. Groups should start by testing the regular sand. Put 50 g of regular sand into the cups and mix with 50 mL of water. Swirl for 30 seconds.
8. Students should take the mass of the sand with water.
9. Remove the extra water by pouring the mixture into another cup through a paper towel. The paper towel should not let the sand through.
10. Measure the mass of the regular sand and record results in the data chart.
11. Repeat steps 7-9 for the other types of sand.

12. Once complete, students should clean up and use the information above to create a bar graph of their results.
13. Have students hypothesize: Why makes this magic sand repel water? [Potential answers: made of different material, has a coating around it, it’s not attracted to water, etc.]

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. The molecular formula for sand is SiO₂ and it is also a polar molecule.

Ask students: If both molecules are polar and thus have charges, what do you think happens when they mix? [they are attracted to one another]

Magic sand is a bit different because it is treated on a nanoscale level to bond with another substance, trimethylhydroxysilane. (At this point, show this website to help students understand how small the nanoscale is: http://htwins.net/scale2/). On a nano-level, these two substances react and make the sand particles nonpolar, which means they have no imbalance of charge.

Ask students: If one molecule is no longer polar, do you think they will attract one another any more? [No]

Elaborate

This can be translated to a discussion of hydrophobic and hydrophilic molecules are seen in other areas of science, particularly capillary action or cell membranes.

This is also a chance to look at other examples of nanotechnology or talk about scientific notation when dealing with nanoscale. (Resource: http://www.nano.gov/education-training/teacher-resources)

Evaluate

Discussion Questions

Do you think molecules can be both hydrophobic and hydrophilic? Why?

Watch this video. 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?

Multiple Choice Items

1. What is the difference between hydrophobic and hydrophilic substances?
   a. Hydrophilic substances attract water, hydrophobic substances repel water*
   b. Hydrophilic substances bond to themselves, hydrophobic do not
   c. Hydrophilic substances repel water, hydrophobic substances attract water
   d. There is no difference
2. Which of these is an example of a hydrophobic substance?
   a. Salt mixes with water and dissolves
   b.Oil is mixed with vinegar but the oil floats to the top
   c.A rain jacket repels water*
   d.A drop of water sits on the side of a glass
3. A correct relationship between polarity and hydrophobic molecules is:
   a.A hydrophobic molecule is nonpolar, so polar water isn’t attracted to it and the substances don’t mix.*
   b.If a molecule is very polar, a hydrophobic molecule will be attracted to it.
   c.A polar molecule will be hydrophobic to a water molecule.
   d.A hydrophobic molecule is nonpolar, so polar water causes charges to attract and water will be attracted to the molecule.

Open-Ended Questions

When washing dishes, many of the items being rinsed off of plates are hydrophobic particles. How do you think a large molecule with hydrophobic and hydrophilic parts might help to clean the dishes? [Usually oils and fats left from food or other substances are hydrophobic. Soap must do something to make these particles more hydrophilic, enabling them to be carried away by rushing water]

Nontechnology calls for scientists to manipulate materials at a nanoscopic level to change the properties of a substance. What practical possibilities could exist for uses of nanotechnology? [making substances more/less resistant to heat/cold/extreme temperatures, strengthening materials’ electrical capacity, strengthening materials for protection, etc.]

Cross-Disciplinary Extensions

Connect to Math

Discuss how scientific notation is constructed in regards to scale.

Connect to Social Studies

Connect the use of magic sand to oil spill cleanup (in the past) and its use in the Arctic by companies.

Next Generation Science Standards

This lesson supports the following:

• Practices of Science and Engineering
• Planning and carrying out investigations
• Analyzing and interpreting data
• Constructing explanations and designing solutions
• Obtaining, evaluating, and communicating information

Crosscutting Concepts

• Cause and Effect: Mechanism and Explanation
• Scale, Proportion, and Quantity
• Structure and Function

Disciplinary Core Ideas, Grades 6-8

Physical science

• Substances are made from different types of atoms, which combine with one another in various ways. Atoms form molecules that range in size from two to thousands of atoms. (MS-PS1-1)
• Solids may be formed from molecules, or they may be extended structures with repeating subunits (e.g., crystals). (MS-PS1-1)
• Each pure substance has characteristic physical and chemical properties (for any bulk quantity under given conditions) that can be used to identify it. (MS-PS1-2),(MS-PS1-3)
• Substances react chemically in characteristic ways. In a chemical process, the atoms that make up the original substances are regrouped into different molecules, and these new substances have different properties from those of the reactants. (MS-PS1-2),(MS-PS1-3),(MS-PS1-5)

Earth science

• Typically as human populations and per-capita consumption of natural resources increase, so do the negative impacts on Earth unless the activities and technologies involved are engineered otherwise. (MS-ESS3-3),(MS-ESS3-4)

Life science

• Within cells, special structures are responsible for particular functions, and the cell membrane forms the boundary that controls what enters and leaves the cell. (MS-LS1-2)

Engineering Design

• The more precisely a design task’s criteria and constraints can be defined, the more likely it is that the designed solution will be successful. Specification of constraints includes consideration of scientific principles and other relevant knowledge that are likely to limit possible solutions. (MS-ETS1-1)