Lab Report - Eva Varga

Chemistry is great for making many useful products. It’s also good for making stuff that’s just fun to play with. One of my favorite chemistry units is on polymers.

A polymer is a large molecule, or macromolecule, composed of many repeated subunits. In other words, they are made up of many, many molecules all strung together to form really long chains.

In Greek, Poly- means “many” and -mer means “part” or “segment”. Mono means “one”. So, monomers are the individual molecules that can join together to make a long polymer chain.

A single polymer molecule is made out of hundreds of thousands (or even millions!) of monomers. Not all molecules can link up in this way to form polymers, however.

The atoms that make up a polymer chain essentially line up and repeat all along the length of the polymer chain. For example, look at polypropylene:

Polypropylene is made up of just two carbon atoms repeated over and over again. One carbon atom has two hydrogen atoms attached to it, and the other carbon atom has one hydrogen atom and one pendant methyl group (CH₃).

In this example, the pendant group hangs from the carbon atom in the chain backbone. As you can see from the example, pendant groups usually repeat along the length of the chain as well.

But enough of the mumbo jumbo. Let’s get to the fun stuff. What is better than reading about chemistry? Doing the labs, of course! Here are three tried and true recipes for polymers you can use in the classroom.

Polymer Recipes ~ Get Messy!

Basic Polymer Putty

This is a fun and easy polymer to make (and the one featured in the photographs).

Materials

Elmer’s white glue
Borax (find in the laundry detergent aisle of the store)
Water
Two bowls
Food coloring (just for fun)

Procedure

In one bowl mix 1/2 cup (4 oz) glue and 1/2 cup water. Add food coloring if you want colored slime.
In the other bowl, slowly mix borax into 1 cup of water until the borax will no longer dissolve (this is a saturated solution).
Add the glue mixture to the borax solution, stirring slowly.
The slime will begin to form immediately; stir as much as you can, then dig in and knead it with your hands until it gets less sticky. Don’t worry about any leftover water in the bowl; just pour it out.

The glue has an ingredient called polyvinyl acetate, which is a liquid polymer. The borax links the polyvinyl acetate molecules to each other, creating one large, flexible polymer. It will get stiffer and more like putty the more you play with it.

Store it in a plastic bag in the fridge, to keep it from growing mold.

A Firmer Polymer

This recipe makes a firmer, dryer slime that will even bounce if it is kneaded enough.

Mix 4 tsp. (20 ml) water with 5 tsp. (25 ml) Elmer’s or other white glue in a small bowl.
Add 1 tsp. (5 ml) talcum powder and stir until thoroughly mixed.
Add 1 or 2 tsp. (5 or 10 ml) saturated borax and water solution. Stir four a few minutes.
Remove the glob from the bowl and stirrer. Knead it for a while and it will become drier.

You will probably need to wipe off some of the excess moisture from your hands with a paper towel from time to time. Don’t be tempted to wipe the glob with a paper towel as it will only stick. You can add a little talcum to the surface if you are having trouble getting it dry enough. Store in a zip lock in the fridge.

Take a closer look at plastics & polymers

Super Slime

This slime is similar to the one above, but creates a less rubbery and more transparent slime. This is the real gooey deal! (This slime is non-toxic, but still keep these chemicals away from unsupervised children and wash your hands after playing with the slime.)

Materials

Polyvinyl Alcohol (PVA)
Borax
Water
Graduated cylinder or measuring cups and spoons
Food coloring (just for fun)

Procedure

Make a 4% solution of polyvinyl alcohol: Stir 1.5 teaspoons (approx. 4g) of PVA into 1/2 C (approx 100 ml) of water in a large microwave-safe bowl. Cover the bowl and microwave for 1 minute, then stir. Microwave another 30 seconds and stir. Continue until all the PVA is dissolved. A slight film may have formed on top; you can remove that with a spoon. You can add food coloring if you want colored slime. Allow the solution to cool.
Make a 4% borax solution by stirring a little less than 2 teaspoons (approx. 4g) of Borax into 1/2 cup of water.
Pour the cooled PVA solution into a ziplock bag and add 2 teaspoons (10ml) of the borax solution.
Zip the bag and knead it until the chemicals are mixed into slime. Then scoop it out and play with it.

While water is a liquid made up of individual H2O molecules, polyvinyl alcohol is formed of long chains of connected molecules, making it a liquid polymer. The borax acts as a “cross-linker,” linking the individual PVA chains to each other. The borax molecules form hydrogen bonds with molecules present in the PVA chains. The partial positive charge of hydrogen atoms attracts the partial negative charge of oxygen atoms. Since hydrogen bonds are weak, they can break and reform as you play with the slime or let it ooze on a flat surface.

Your slime will last for a while if you seal it in a plastic bag and keep it in the fridge.

Learn how to dispel children’s Misconceptions in Chemistry & Physics.

Helpful Hints for Success with Polymers

Gel type glues

Over the past few years several brands of gel type glues have been introduced. Most of these make excellent slimes which are very elastic and have a nice color and consistency. I have personally experimented with Elmer’s School Glue Gel, but there are several similar products available from other manufacturers. Try substituting a gel glue in the Basic Polymer recipe, above.

Slime overly sticky or runny?

If your white glue or gel glue based slime is too sticky or runny, first try kneading it for a while. Working it in your hands will help to mix things up better, as well as remove some of the moisture. If it is still not quite right, mix 1 part borax with 10 parts water. Dunk the slime into this solution, remove and knead.

Precautions

Polymers can wreak havoc with plumbing, so don’t throw them down the drain.
Always wear a mask when mixing PVA.
Use distilled water for all solutions for best results.
Keep polymers away from anything they could damage. They can dry into fabric and the dyes can stain surfaces, including wood.
Supervise small children when playing with polymers so they do not ingest any.
Some people are allergic to Borax powder. Wearing rubber gloves when mixing should help.
Polymers using Borax solutions work best if you pour the Borax solution into the other solution, rather than the other way around. Coloring should be added before the Borax.
Use metric measurements whenever possible. This will make it simpler to experiment with different concentrations and ratios.

For more hands-on chemistry lessons like this one, check out Cool Chemistry is a ten-week multidisciplinary, hands-on physical science curriculum that incorporates scientific inquiry and a long-term project. Available today!

Last year, for the first time, we took part in Physics Quest, a story-based activity that aims to teach middle school students physics concepts and give them a positive experience with physics. When the kit arrived, we jumped right in!

Physics Quest began as a World Year of Physics 2005 project with a kit based on Albert Einstein. The American Physical Society (APS) sent out nearly 10,000 free kits that year, to classes across the country. Teacher feedback from the initial PhysicsQuest indicated that it successfully met a need for fun and accessible physics material at the middle school level, therefore APS decided to continue the program.

Spectra: High Intensity

In celebration of the International Year of Light, the 2015 kit, Spectra: High Intensity, provided the equipment needed to teach students about bending light, spherical lenses, how color and energy are related, and how the sun’s light also carries heat. We spent an entire day reading the story and exploring these physics concepts.

In Spectra: High Intensity, the storyline begins with the students learning that Miss Alignment had broken out of jail and was on the loose hatching evil plans. “Armed with a high IQ, an inferiority complex, and a secret lair, she will try yet again to control the town.”

Working together as a team, my kiddos completed the activities outlined in the book. In doing so, they applied the skills they need to help Spectra and her gang prevent Miss Alignment’s attempted town domination. It was great fun and the hands-on activities were perfectly designed for their age.

Sign Up Today

APS provides a free Physics Quest kit to registered 6-9th grade physical science classes, home school groups, science clubs, and after-school programs. The kit includes a user’s manual and materials for four physics experiments. This program focuses on middle school students because these grades have been identified as the point when many students lose interest in math and science.

Registration is now open for the 2016 PhysicsQuest, Spectra’s Current Crisis.

Whenever I teach introductory chemistry, one of my favorite activities is to create rock candy. Rock candy is formed by allowing a supersaturated solution of sugar and water to crystallize onto a surface suitable for crystal nucleation, such as a string or stick.

STEM Club kids were delighted the day I told them we were making rock candy in class. Sadly, our “experiment” didn’t turn out as expected.

Words to Know

Mixture :: A mixture is simply a combination of two or more substances that do not react to form something new. For example, mud, cake batter, milk, salad, latex paint, black top (asphalt and gravel). Mixtures are combinations of compounds that can be separated by mechanical or physical processes. If the atoms can only be separated with chemical reactions, they are complex molecules, not mixtures.

Solution :: A special kind of mixture called a solution is where mixing occurs at the molecular level. Examples are sea water, Kool-Aid, antifreeze, seltzer water, and gasoline.

In a solution, one or more substances are dissolved into another substance. In the example of Kool-Aid, the sugar and mix are dissolved into water. The substance that gets dissolved is referred to as the solute. The substance that dissolves a solute is referred to as the solvent. A solvent is usually a liquid but can also be a solid or a gas. In this example, Kool-Aid is the solute and water is the solvent.

All solutions are mixtures, but not all mixtures are solutions. Solutions are homogeneous mixtures (uniform in composition or character).

Saturated Solution :: A saturated solution is one in which no more solute can be dissolved.

Supersaturated Solution :: The physical properties of a compound can change when other substances or compounds are added. The melting or boiling point can increase or in some cases decrease. Raising the temperature of a compound (water for example) will enable you to dissolve more sugar into the solution. This creates a super-saturated solution.

How to Make Rock Candy

Materials

2 cups water
4 cups granulated sugar
1/2-1 tsp flavoring extract or oil (optional)
food coloring (optional)
glass jar
wooden skewer and a clothespin

Procedure

1. Wash a glass jar thoroughly with hot water to clean it. Wet the skewer, and roll it in granulated sugar. This base layer will give the sugar crystals something to “grab” when they start forming. Set the skewer aside to dry while you prepare your sugar syrup.

2. Place the water in a medium-sized pan and bring it to a boil. Begin adding the sugar, one cup at a time, stirring after each addition. Heating the water before adding the sugar allows more sugar to dissolve thus producing larger crystals.

You will notice that it takes longer for the sugar to dissolve after each addition. Continue to stir and boil the syrup until all of the sugar has been added and it is all dissolved. Remove the pan from the heat.

3. If you are using colors or flavorings, add them at this point. If you are using an extract, add 1 tsp of extract, but if you are using flavoring oils, only add ½ tsp. Add 2-3 drops of food coloring and stir to ensure even, smooth color.

4. Allow the sugar syrup to cool for approximately 10 minutes, then pour it into the prepared jar. Suspend the skewer into the solution about 1 inch from the bottom.

5. Carefully place your jar in a cool place, away from harsh lights, where it can sit undisturbed. Cover the top loosely with plastic wrap or paper towel.

7. You should start to see sugar crystals forming within 2-4 hours. If you have seen no change to your skewer or thread after 24 hours, try boiling the sugar syrup again and dissolve another cup of sugar into it, then pour it back into the jar and insert the string or skewer again.

8. Allow the rock candy to grow until it is the size you want. Once it has reached the size you want, remove it and allow it to dry for a few minutes, then enjoy or wrap in plastic wrap to save it for later.

Our Results & What We Learned

As we were underway, my thought was, “I don’t want a dozen jars of sticky sugar syrup on my counter for the next week or so. We may as well put all the skewers into the same jar – one for every student.”

I clearly didn’t think this through. As the water evaporated, the crystals grew and expanded. Eventually, they merged and even began to grow onto the sides of the jar. I was unable to remove the skewers and a few even broke off from the tension as I tried to pull them out.

I tried using a knife to break apart the crystals. I even placed the jar into a water bath in an attempt to reheat the solution and melt the crystals. Can you guess what happened?

Yep! The jar broke!! Even though it was a pressurized Kerr canning jar. Yikes!

We thereby learned it is best to suspend a single skewer into a glass of sugar solution to avoid crystal conglomeration. Keep an eye on the progress – don’t let it grow too large. You don’t want the crystals to reach the bottom or you’ll have difficulty removing the skewer.

Cultural Notes

Rock candy is a common ingredient in Chinese cooking, and many households have rock candy available to marinate meats and add to stir fry. It is used to sweeten Chrysanthemum tea and Cantonese dessert soups. It is also an important part of the tea culture of East Frisia and Tamil cuisine in India.

If you enjoyed this activity and would like to expand on the concepts introduced here, I encourage you to check out my 10-weekmultidisciplinary, hands-on chemistry curriculum, Physics Logic: Cool Chemistry.

Mud, or sediment, is an active part of aquatic ecosystems. Sediment varies widely within and among ecosystems in its biotic and abiotic characteristics.

Biotic factors are the living components of a community or larger ecosystem.

Abiotic factors are essentially non-living components that effect the living organisms of a community.

In many ecosystems sediment can release excess phosphorus (a common aquatic pollutant) into the water column causing internal eutrophication.

When studying aquatic ecosystems, people often think about the water and things that live in the water. However, the mud at the bottom of lakes and wetlands – the sediment – is an active part of these ecosystems. A wide diversity of organisms, both macroscopic and microscopic, live in sediments.

Sediments can often be a source of nutrients, especially nitrogen and phosphorus. Nutrients released from sediments are part of an ecosystem’s internal load (as opposed to the external load, which consists of nutrients that come from outside the ecosystems).

Most commonly, sediments release large amounts of phosphorus as phosphate, sometimes causing excessive algal growth, harmful algal blooms (growth by algae that produce toxins), and even fish kills (as dead algae fall to the bottom of an ecosystem, fuel bacterial decomposition, and consume oxygen). These negative effects caused by sediment release of phosphorus are called internal eutrophication.

Life in the Mud

Gather around a picnic table at a local pond or wetland area. Lead the class in a discussion about how the abiotic and biotic components of the pond could interact. Use what the students have said to link the nutrient content of the sediment and water to the activity of living things in the water. For example, nutrients released from the sediment can enhance growth of algae in the water.

Ask students to hypothesize about what they expect to see in the mud. What makes up the sediment? What makes up the pond water? Describe some possible interactions between the sediment and the water column.

Materials

2 quart jars with lids for each group
Mud from a pond (enough for about 1/3 of each of the jars)
Water from a pond–algae WILL be there (enough to fill the other 2/3 of each of the jars)
Shovel (one for each group)
Water quality kits for measuring nutrients for each group
Compound microscope (for each pair of students)
Microscope slides
Optional Materials: Dissolved oxygen meter, dissecting microscope, thermometer, conductivity meter, funnel

Experimental Set Up

Split into small groups and distribute materials evenly. Each group should disperse to a different area around the pond perimeter to begin the experimental set up.
Each group should utilize the water quality kit to test the pond water and record the data in their journals.
Each group sets up the jars: one with nothing but pond water in it (control group) and another jar with 1/3 pond sediment and 2/3 water in it (treatment).
After collecting mud samples, return to the table. Lead students through the process of developing a hypothesis with the guiding questions: What differences do you expect to see in the treatment group and control group in about a week? Why do you think those differences might occur? Possible hypothesis: There will be a greater number of algae in jar with sediment and pond water compared to the jar with only pond water.
Check the jars after one week. If you do not see obvious responses, check them again after two weeks as it may take some time for visible algal growth to occur.

Data Collection

Qualitative Observations: appearance of the water and sediment, look for evidence of algae growth—cloudy water and green “slime” on the sediment; any bubbles coming from the sediment, smell, layers in sediment evidenced by color difference or texture changes; macroscopic organisms in either sediment or water; bacterial growth (slime).
Quantitative Observations: use a microscope to count the algal cells in the water in each jar; if available, test the water in each jar with any available nutrient water testing kit (nitrogen and/or phosphorus), depth of water and sediment over time, water temperature, conductivity and dissolved oxygen, pH.

If you would like to do undertake this outdoor lab activity with you students, I’ve created a free printable student page, Life in the Mud, for your use. If you download it, please leave a little note in the comments.

Soil is rarely devoid of life. Soil which supports plant life is teeming with many soil organisms, the majority of which are too small to see. Some examples of soil organisms are fungi, bacteria, nematodes, diatoms (algae), earthworms, ants, centipedes, millipedes, beetles, snails, and slugs. All these soil creatures and more make up the soil community. In STEM Club, we sought to discover for ourselves, what lives in our soils?

Most fungi and bacteria are supported by relationships with plant roots, so they stay close to plants. Any creatures that live on fungi and bacteria also stay close to the roots. Other larger herbivores, like beetles, ants, centipedes, and termites, feed closer to the surface where more plant debris is located.Therefore most soil creatures live within a few inches of soil closest to their food sources.

This community of organisms is deeply involved in the soil food web. It’s basically a recycling program, where plant and animal residues are broken down by a chain of soil consumers (nematodes, bacteria, fungi, mites, earthworms, etc), who are then consumed by birds and other mammals, cycling carbon and essential nutrients.

Soil protects soil organisms from harsh sun, wind and, rain, while still providing air, water, and nutrients essential to life. When soil organisms break down plant and animal debris they change the structure of the soil. Creatures like earthworms break down larger vegetative clumps into smaller clumps of organic matter, making the soil structure finer. In a good plant debris-based soil, the actions of earthworm, as well as the amount of organic matter, greatly increases the soil’s ability to hold nutrients and water, as well as structure (pores).

Soil lacking in oxygen, water, and organic matter would be very bare and devoid of biodiversity. The area would consist only of a few, very specific kinds of soil organisms and specific plants that could tolerate these challenging environmental conditions.

What Lives in Our Soil?

Can you think of any other examples of food webs? What are some reasons why a soil would not have a layer of organic matter or humus near the surface? What would be some environmental strategies to remedy such a soil? What would happen if a group from the soil food web (fungi, animals, plants, insects, earthworms) suddenly disappeared?

The goal of this activity is to discover what lives in soil. Students will select a location to collect a soil sample, return to the classroom, and thereby note a variety of characteristics of the soil (moisture content, texture, color, etc.).

Materials

Small shovel(s) or trowel(s)
1-liter plastic freezer bags
Plastic jars
Magnifying glasses
Permanent marker
Journals
Map of school grounds, town, or county (geographically and by elevation)

Procedure

1. Preparation :: Take note of locations that the students would be interested in taking samples from. Be sure to have a variety of locations:

Garden or flower bed
Wooded area
Near a parking lot
Near a sidewalk
Turf (grassy area)

Have a table in the classroom or other open space ready for observing soils. If students will be drying soil, you’ll need a place where soils can be left for several days
Have students draw a map of the school grounds.

2. Digging Soil :: At each selected area, have students:

Observe location and vegetation
Describe location and vegetation orally
Write about location and vegetation in journals
Use trowel or shovel to collect several clumps of soil
Place soil in freezer bags

3. Observations :: Place soil samples on table or other open space. Divide students into groups and distribute one soil sample bag per group. Observe characteristics of the soil
which may include:

Gravel
Rocks
Sand
Earthworms
Ants
Other soil creatures
Color
Moisture
Texture

4. Record observations by location on chart (sample below). Predict from chart which soils might be best for growing crops.

Extension Activities

Develop an inquiry project to further investigate your prediction in step 4.
Choose a soil organism and write an expository paragraph (include: name, appearance, role, supporting details, and conclusion).
Think of three animals that live in the soil and the homes they build. Students draw a soil community that includes small creatures, creatures above the soil, and plants.
Create an informative poster to illustrate the soil food webs (include at least five trophic levels).

You can learn more about the activities we undertook in STEM Club here:

Soil Ecology Activities for Middle School

Cycles and Ecosystems {Free Printable}

Rain Gardens & Composting

Soils Support Agriculture: Ideas to Integrate Writing

Let’s Get Dirty: Soil Horizons & Particle Size

Let’s Get Dirty: Life in the Mud

Soil is the part of the ground where plants grow. Soil is a mixture of tiny particles of rock and rotting plant and animal material, with water and air between them. Soils help plants grow in two ways. First, soil holds the plants into place. Second, soil contains nutrients that plants need in order to survive. These nutrients include water, phosphorous, nitrogen, and potassium.

Over the course of the next few weeks, STEM Club will be investigating soil ecology as a part of the Year of Soils. I’ve shared a few of our past endeavors relating to soils here:

Soil Ecology Activities for Middle School

Cycles and Ecosystems {Free Printable}

Soils Support Urban Life: Rain Gardens & Composting

Soils Support Agriculture: Ideas to Integrate Writing

STEM Club: Let's Get Dirty (Soil Ecology) @EvaVarga.net

Today, I share a lesson on soil horizons and particle size.

Soil Horizons

Soil particles vary greatly in size. The largest particles settle to the bottom first. The fine particles settle slowly; some are suspended indefinitely. The amount of open space between the particles has much to do with how easily water moves through the soil. This also determines how much water the soil will hold, which has a major effect on the type of plants that can grow in the soil.

Things to look for in soil are color, texture, structure, depth, and pH. A general soil profile is made up of a litter layer, A horizon, B horizon and C horizon. A soil sampling device (pictured in the collage above) allows you to gather data on the soil makeup on any site.

Soil Particle Size

Soil scientists classify soil particles into sand, silt, and clay. Scientists use these three components and the calculated percentages on the texture triangle to determine the textural class of the soil at a given site.

A soil’s texture depends on the size of its particles and living things depend on the right texture to thrive in the soil. Every soil type is a mixture of sand (2mm – 0.05mm; feels gritty), silt (0.05 – 0.002mm; feels like flour), clay (Smaller than 0.002; feels sticky when wet), and organic matter. Squeeze some soil between your fingers. Is it crumbly? Sticky?

Let’s Get Dirty ~ Terrestrial Soils

One of the best activities to engage kids in the study of soil ecology is the sample the soils around your home or school yard. Begin by asking the following questions:

1. Are there different types of soil near your home?

2. What texture class is this soil?

3. What is the particle size make-up of this soil?

The answers generated prior to the investigation are part of your hypothesis. Record your ideas in your science notebook before you begin and give reasons. Why do you suppose the soil in your yard is predominately sand? What experience or prior knowledge do you have to help you make this statement?

Materials

1 Soil probe
1 Metric ruler
1 Quart jar with lid
1 Set index cards for diagrams

Procedure

Use the soil probe to collect soil cores as deep as possible from a predetermined site.
Diagram and measure the depth of each layer or horizon in your sample.
Fill the quart jar at least half and no more than two thirds full.
Fill the rest of the jar with water, seal tightly and shake vigorously for 10 minutes. Let the jar stand for 24 hrs.
The next day, mark the soil layers of each sample on an index card placed behind the bottle. Mark the top of the soil and the points where the layers change. Calculate the percent of sand, silt and clay in your sample. To do this, measure the following marks you made on the card: entire height, sand (bottom) layer, silt (middle) layer, and clay (top) layer. Then take the height of each layer by the total height and multiple by 100. Record the figures on the data sheet.

Analysis of Results

At which site was the soil the most sandy? silty? mostly clay?
Do you think that this is a trend and would be found at other sites? Explain.
What are some factors that may change the results of this experiment? Explain.

Conclusions

Did you achieve your hypothesis? Explain.
What did you learn by doing this exercise?
Do you think the soil will be the same at other sites (park, forest, meadow, near the shore of a lake or river, etc.)? Design an inquiry project to learn more.