In this lesson, students will investigate the properties of magic sand and learn about the concept of hydrophobic and hydrophilic molecules. It also introduced students to the field of nanotechnology.
By the end of this lesson, students should be able to
- differentiate the terms hydrophobic and hydrophilic.
- explain how shifting the properties of substances on a nano-scale can result in drastic changes of chemical and physical properties.
- create a data chart and bar graph based on their observations of magic sand.
This lesson supports students’ understanding of the following topics in chemistry:
- Physical changes
Teacher Preparation: 10-15 minutes
Lesson: 40-60 minutes
- For teacher demonstration and material prep:
- Clear small aquarium or plastic cube (must be see-through)
- One container of magic sand (can be purchased)
- One can of Scotch Guard or other fabric protector (spray samples of regular sand down with this prior to class twice over, let dry)
For each group:
- 50 g (or more) of magic sand
- 50 g of regular sand
- 50 g of sand sprayed with Scotch Guard
- Cups and containers to hold the types of sand
- Markers (to label the cups)
- Graduated cylinder
- Paper towels
- Students should be warned to not eat the magic sand.
- Safety goggles should always be worn when carrying out lab activities.
Polarity, nanotechnology, magic sand, hydrophobic, hydrophilic, nonpolar
- A brief background on magic sand can be seen here
- To maintain students’ attention, it may be helpful to have time set aside for them to play with the magic sand aside from during the Enhance section
- Keep the magic sand (and really, any sand) away from students until it comes time for the activity to minimize distractions.
- Clearly label all cups, or dye the Scotch Guard covered sand to differentiate it from the magic sand and normal sand
For the Student
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.
- Explain to students the difference between hydrophobic and hydrophilic substances. Use the Latin prefixes and suffixes to help (hydro-, -philic, -phobic)
- Ask students: Is the sand in the aquarium hydrophobic or hydrophilic? Why? [hydrophobic, it repels water]
- Ask students: What are some other examples of hydrophobic substances? [coating of rain jackets, oil]
- Tell students that they will test how hydrophobic or hydrophilic three substances are—regular sand, sand covered with a fabric protector, and magic sand
- Split students into groups of 3–4 and have each group obtain the materials above.
- Have students label the cups Regular Sand, Protected Sand, and Magic Sand.
- 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.
- Students should take the mass of the sand with water.
- Remove the extra water by pouring the mixture into another cup through a paper towel. The paper towel should not let the sand through.
- Measure the mass of the regular sand and record results in the data chart.
- Repeat steps 7-9 for the other types of sand.
|Type of Sand||Mass of Sand Before Water||Mass of Sand With Water||Mass of Sand After Water is Removed||How wet does the sand look/feel? Give evidence!||Hydrophobic or hydrophilic?|
|Regular Sand||50 g|
|Protected Sand||50 g|
|Magic Sand||50 g|
- Once complete, students should clean up and use the information above to create a bar graph of their results.
- 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.]
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]
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)
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
- 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
- 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
- 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.
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.]
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
- Cause and Effect: Mechanism and Explanation
- Scale, Proportion, and Quantity
- Structure and Function
Disciplinary Core Ideas, Grades 6-8
- 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)
- 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)
- 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)
- 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)