session 1 – introducing molecules and atoms
periodic table, what have you heard of, any others – various metals, oxygen etc, then h2o, co2 etc and make a variety with marshmallows/ sweets on sticks. look at structure of atoms. some children proton, neutron and electrons.
session 2 – reactions!
1. volcano – bicarb vinegar
http://chemistry.about.com/cs/howtos/ht/buildavolcano.htm
The experiment baking soda and vinegar is one of the most popular. However, it is deceptively simple: what appears to be one reaction is actually two, happening in quick succession. This reaction is an example of a multi-step reaction.
What actually happens is this: the acetic acid (that’s what makes vinegar sour) reacts with sodium bicarbonate (a compound that’s in baking soda) to form carbonic acid. It’s really a double replacement reaction. Carbonic acid is unstable, and it immediately falls apart into carbon dioxide and water (it’s a decomposition reaction). The bubbles you see from the reaction come from the carbon dioxide escaping the solution that is left. Carbon dioxide is heavier than air, so, it flows almost like water when it overflows the container. It is a gas that you exhale (though in small amounts), because it is a product of the reactions that keep your body going.
What’s left is a dilute solution of sodium acetate in water.
2. volcano lava lamp
dilute vinegar and 1/3 fill jar, oil on top and add food colouring. then sprinkle teaspoon of soda and enjoy…
session 3 extracting dna
sessions 4 and 5 polymers
A polymer is a large molecule, often containing many thousands of small molecules joined together chemically to form one giant macromolecule. While the terms macromolecule and polymer are used synonymously, you will see the word polymer used more often.
Amazing Polymers
In the flubber experiment, borax starts out as a solid but creates a mixture with the glue and water. The glue is also a liquid. When they are combined, they create a colloid polymer.
diagram of a polymer colloidA colloid is a mixture where the particles are too large to dissolve but small enough to remain suspended in the liquid. A polymer is a long chain of molecules that look something like strands of cooked spaghetti. With a polymer colloid, the suspended particles are long polymer strands.
diagram of a polymer colloid with linksIf the polymer chains slide past each other easily, then the substance acts like a liquid, because the molecules flow. If the molecules hook together at a few places along the strand, then the substance behaves like a rubbery solid. Borax is responsible for hooking the glue’s polymer molecules together to form the putty-like material (picture 2 shows the borax linking the long polymer glue chains).
When you stretch the putty, it stretches without breaking, but can be “snapped off” cleanly. It bounces higher than a rubber ball, with a rebound of 80%. If you hit it with a hammer, it keeps its shape, but pushing it with light pressure flattens it easily.
If you just let the putty sit or squish it with your fingers, the molecules slide over each other and the material flows. When you drop it like a rubber ball, the impact tries to make the molecules move past each other very fast. It doesn’t work. They’re too tangled.
Review of Scientific Principles:
If a substance springs back to its original shape after being twisted, pulled, or compressed it is a type of polymer called an elastomer. The elastomer has elastic properties. It will recover its original size and shape after being deformed.
The liquid latex used contains small globules of hydrocarbons suspended in water. Joining these globules forms the mass with which the students will be working. The covalent bonds along the chain are strong, but the bonds between chains are normally weak. However, additives such as borax allow the formation of strong “cross-links” between chains, such as C-B-C. As the number of cross-links increases, the material becomes more rigid and strong.
If the rigidity of a polymer is noticed to decrease when a critical temperature is reached, the polymer is called a thermoplastic. If the bonds between polymer molecules are very strong, the material decomposes before any softening occurs. Such a material is called a thermoset plastic.
Natural sources of this liquid latex are milkweed, rubber trees, pine trees, aloe plants, and many desert plants. This latex is used to quickly mend and repair any damage to the outer covering of the plant.
Procedure for Making a Polymer Ball from White Elmer’s® Glue-All and Borax Powder:
1. Measure 30 mL (2 tbsp) of glue into a plastic cup with the 30 mL level marked.*
2. Add approximately 1 gram (1/2 tsp) of Borax powder to the glue.
3. Stir vigorously until the mixture clumps and sticks to the stirring rod or stick.
4. Remove the clump of polymer from the stick. Hold it under running water and shape into a ball.
5. Pat the ball dry and bounce it on the table top.
6. Save for activities.
*Prior to use, the 30 mL mark can be determined by adding 30 mL of water, (measured in a graduated cylinder) to the cup. The level can be marked, and the cup emptied and dried.
Instructions on How to Make a Polymer Ball from Liquid Latex and Vinegar:
NOTE: This procedure should be done under a fume hood or in a well-ventilated area.
1. Measure approximately 15 mL (1 tbsp) of liquid latex rubber into a marked plastic cup.*
2. Pour 15 mL (1 tbsp) of water into the liquid rubber and stir to mix.
3. Using a dropper, slowly add 15 mL (1 tbsp) of 5% acetic acid solution (household vinegar) to the latex, while continuously stirring.
4. When the mixture takes on the consistency of “rubber,” remove it from the cup. Hold it under running water and shape into a ball.
5. Pat the ball dry and bounce it on the table top.
6. Save for activities.
*Prior to use, the 15 mL mark can be determined by adding 15 mL of water, (measured in a graduated cylinder) to the cup. The level can be marked, and the cup emptied and dried.
Physical Appearance: Describe the texture, color, smell, and other observable characteristics.
Comparisons: Compare the different types of balls, OR compare the same type of ball made by different students.
Bounce: Bounce the ball and observe its bounce height and the sound it makes. Also try bouncing ball on different surfaces.
Measurements: Find the circumference, radius, diameter, and mass of the sphere.
natural polymer experiments
Polymers are very large molecules, formed by repeated patterns of chemical units strung together. Although “polymer” might bring to mind rubber or slime, did you know that there are polymers all around us, including inside our bodies? The protein DNA, which is the “blueprint” for cellular reproduction, is a naturally-occurring polymer. The protein casein, in cow’s milk, is a polymer as well. Other natural polymers are cellulose and starch. Bone, horn, cotton, silk, rubber, paper, and leather all come from naturally-occurring polymers!
There are manmade polymers, as well. Fabrics such as rayon and polyester, polystyrene (used in styrofoam coffee cups), and PVC (used in pipes) are common examples of these artificially-occurring polymers.
You can use the following recipes to learn more about non-edible, naturally-occurring polymers. (Adult supervision recommended.)
Homemade Glue
Materials
* A tall, clear glass
* Non-fat or skim milk
* White vinegar
* Coffee filters or paper towels
Procedure
1. Did you know you can make glue using the polymers in milk protein? In a glass, put seven tablespoons of non-fat or skim milk €”whole milk contains more fat, which can change the experiment results.
2. Add a tablespoon of white vinegar to the milk; you should see solids begin to form that are suspended in the liquid. The solids will have a grainy appearance. Allow them to settle toward the bottom of the glass, then drain the liquid off, using a coffee filter or paper towel.
3. Now, pat the solids with a paper towel to absorb any excess liquid. You can use the resulting slimy substance as glue–coat two pieces of paper with it, stick them together, and let it dry. How well does your homemade glue work compared to other glues?
When you added the vinegar to the milk, it caused the milk’s protein, the polymer casein, to separate from the liquid part of the milk and clump together to form solids. Casein is used in adhesives, paints, and even plastics.
Polymer Slime
1. You can make a slimy substance using milk, vinegar, and baking soda. Form solids like you did in the glue project, using seven tablespoons of milk and one tablespoon of white vinegar. After the solids have formed within the liquid, use a coffee filter or paper towel to drain off the remaining milk.
2. Gently squeeze the filter or paper towel to wring as much liquid out as possible, and then use a paper towel to soak up any remaining liquid from the clump of solids. Next, mix baking soda with the solids; start with 1/4 teaspoon and then add more if necessary to pull the solids together. Make sure you mix the substance well! The end result should have the consistency and appearance of custard or thick vanilla pudding. Now you have a slime made from the polymers in milk protein!
For a different kind of slime, mix white glue (like Elmer’s) with cornstarch and water. (White glue contains polyvinyl alcohol, a polymer.) Use four parts glue to one part cornstarch mixed with one part water: combine the water and cornstarch, and then add the glue gradually, stirring well. You’ll need to let the mixture stand for several minutes before it turns to a solid putty-like slime.
starch experiment
You will Need:
1 cup cornstarch
1 cup measuring cup
1/2 cup size measuring cup
3-4 cup disposable plastic container with lid (Ziploc, Hefty or Glad make several sizes)
Food coloring (optional)
Plastic spoon
Water (4-8 ounces per group)
Old newspaper to cover your work surface
Step #1
Spread out the newspaper on the work surface
Obtain a large plastic bowl
Measure and pour in 1 cup of dry cornstarch
Add one drop of food coloring (if you wish)
Slowly add 1/2 cup of water
Use your fingers to mix until all the powder is wet
Keep adding water until the “Ookey Oozey” feels like a liquid
Now, try tapping on the surface with your finger or the back of a plastic spoon. When you have your “Ookey Oozey” made correctly, it won’t splash. It will feel solid. If your “Ookey Oozey” is too powdery, add a little more water. If “Ookey Oozey” feels too wet, add cornstarch.
Step #2
Pick up a handful. Is it easy or hard?
Next, squeeze it. What happens?
Stop squeezing. What happens?
Slowly lower your fingers on the surface of the “Ookey Oozey”
Let your fingers rest on the surface
Slowly sink your fingers into the “Ookey Oozey”
Now, try to quickly pull your fingers out. What happens?
Next, take a blob in your hands, roll it between your hands and try to make a ball. What happens when you stop rolling it
session 6 nappy experiment
You can experiment with this superabsorbent powder at home. This is what you need:
* 3 “superabsorbent” disposable diapers (e. g. Ultra Pampers)
* 5-gallon plastic bag, with twist-tie sealer
* kitchen sieve
* 2 water glasses
* table salt
* spoon
First extract the superabsorbent powder from the diaper as follows:
* Cut open the superabosrbent diapers and place the cotton-like filling into the plastic bag. (The filling will feel gritty; the grittiness results from the superabosrbent powder.)
* Seal the bag with a twist-tie.
* By manipulating through the bag, shred the diaper filling until it is in small pieces.
* Rub the filling against itself.
* Shake the bag to loosen the powder from the filling. The powder will settle to the bottom of the bag.
* Open the bag and feel the filling. If it still feels gritty, close the bag and rub the filling again. When the filling no longer feels gritty, gently shake the bag to settle the powder to the bottom of the bag.
* Open the bag and remove the filling. (Take care not to inhale dust of fibers from the filling.) The powder on the bottom of the bag can be separated from most of the remaining pieces of filling by passing it through the kitchen sieve.
* Place the powder in an empty, dry drinking glass and examine it.
o What color is it?
o Is it fine or coarse?
* Fill the second drinking glass with water.
* Pour the water from this glass into the one containing the powder from the diapers.
* Pour the mixture back and forth from one glass to the other. As you pour, the mixture will thicken, and eventually become so thick that it will no longer pour.
o How long does this take?
o What does the thickened mixture look like?
Pouring the thick polymer mixture Sprinkle about a teaspoon of table salt on top of the thickened mixture. Stir the salt into the mixture with a spoon.
*
o What happens as you stir?
o Does the mixture become thin enough to pour again?
o Add more salt and stir some more. Does the mixture become more fluid?
Depending on the size of the particles in the diaper, it may be possible to remove the salt from the superabsorbent material.
Pour the mixture of powder, water, and salt into a sieve lined with a paper towel and slowly run water through sieve. The flowing water will gradually remove the salt. As the salt is washed away, the mixture will thicken. When it has become almost as thick as it was before the salt was added, stop rinsing it and use another paper towel to press the excess water out of the contents of the sieve. If the thickened material in the sieve is placed in an open dish for several days, the water will evaporate from the mixture, leaving the original material from the diaper. This material can be used again to absorb more water.
The powder you extracted from the diapers is a “superabosorbent polymer.” A polymer is a material whose molecules (smallest particles) are a long chain of repeating units. In the superabsorbent polymer, each of these units has a portion that holds an electrical charge. The electrical charges on the polymer attract water molecules and bind them to the polymer. Each charge binds several water molecules and each molecule of polymer can bind a large volume of water. When salt is added to the mixture of water and polymer, the polymer releases the water. This occurs because salt also contains electrical charges. The charges in salt also attract water molecules, and water molecules bind to the salt instead of the polymer. Furthermore, the charges in salt are attracted to the charged parts of trhe polymer and displace of the molecules of water from the polymer.
Technical notes
1 The water crystals are available from garden centres and are sold under various names including Phostrogen Swellgel. Each group needs about a teaspoonful.
2 For the strong tea use two tea bags per litre, pour on boiling water and leave to brew overnight. This tea stains some containers.
3 If distilled water is not available, tap water can be used but the results are not as spectacular.
Procedure
HEALTH & SAFETY: Wear eye protection
Part 1
a Estimate the volume of the water crystals.
b Put about 500 cm3 of tea, tap water or water coloured with a few drops of food colouring into the beaker or tub. Add one teaspoonful of water crystals, stir gently and leave on one side for at least half an hour, or overnight.
Part 2
a Sieve the water crystal mixture. It is best to do this over a large tub rather than the sink in case you drop it. Wash the gel crystals carefully once or twice in water to remove any excess tea or food colouring if you used it. Estimate the new volume of your crystals.
b Stand the three 250 cm3 beakers on a piece of white paper.
c Put two dessert spoons of the gel crystals into each beaker, estimate their volume and then add about 200 cm3 of salt solution to one and 200 cm3 of distilled water to each of the others. Add a spoonful of sugar to one of the beakers with water in it. Label the beakers.
d Stir the mixtures gently – using a separate stirring rod for each one so that the solutions do not become cross-contaminated. Leave for 10–15 mins, stirring occasionally.
e If you used tea, pour some of the solution from each beaker into a petri dish placed on the white paper. Use a tea strainer to prevent any crystals getting onto the petri dish. Note carefully the colour of each liquid.
f Sieve the remaining mixtures, discarding the excess liquid and returning the crystals to the beakers. Estimate their new volumes.
Teaching notes
This activity can be used to enhance the teaching of ionic and covalent bonding, or hydrogels can be considered as an interesting polymer as well as an example of a smart material. Hydrogels are smart materials because they change shape when there is a change in their environment – in this case it is the change in the concentration of ions.
Students need to have some knowledge and understanding of ionic and covalent bonding, reversible reactions, and acids and bases to understand what is happening.
Hydrogels are polymers that can retain many times their own weight in water. They are often polymers of carboxylic acids that ionise in water, leaving the polymer with several negative charges down its length. This has two effects. First, the negative charges repel each other and the polymer is forced to expand. Secondly, polar water molecules are attracted to the negative charges. This increases the viscosity of the resulting mixture still further as the polymer chain now takes up more space and resists the flow of the solvent molecules around it.
hydrogels Plant Water
The polymer is in equilibrium with the water around it, but that equilibrium can be disturbed in a number of ways. If the the ionic concentration of the solution is increased – eg by adding salt – the positive ions attach themselves to the negative sites on the polymer, effectively neutralising the charges. This causes the polymer to collapse in on itself again. Adding alkali removes the acid ions and moves the equilibrium to the right; adding acid has the opposite effect.
There are a large number of hydrogels and they are sensitive to different pHs, temperatures and ionic concentrations. By using a mix of monomers to create the polymer these characteristics can be fine-tuned.
The hydrogels that are commonly available and are used in this practical activity are sensitive to salt concentration, but do not show much change across the pH range that can be readily investigated in the classroom. However, they do lend themselves very well to a range of investigative practical work. For example, their volume in different amounts of water or in different salt concentrations can be measured. For this type of investigation it is best to use either plant water crystals or to order sodium polyacrylate (Low hazard) from Sigma Aldrich – this has a smaller crystal size and gives faster results.
Students should make detailed notes on their experiments, noting changes in volume, colour and any other observations. Some expected observations could include:
The crystals swell up from about 5 cm3 to about 500–600 cm3. They take on the colour of the tea (or food colouring), showing that the tea has also been absorbed.
When distilled water is added to the hydrated crystals, they swell up further. The tea remains absorbed in the crystals and the water does not change colour. When salt water is added to the hydrated crystals, they begin to shrink and the water changes colour as the tea is released. It is possible to measure the aproximate size of individual pieces of the hydrogel too, and to show that the pieces have swollen or shrunk. The hydrated crystals in the sugar solution have the same volume as the ones in the distilled water. If they are left for up to 15 mins the tea is not released. (After this time, the water in the hydrated crystals is in equilibrium with the water in the beaker and some tea may begin to be observed.)
These observations show that the hydrogel responds to changes in the ionic concentration of the solution – the salt, which is ionic, causes the hydrogel to collapse but the covalent sugar does not.
Research is currently being done to see if it is possible to use hydrogels and similar materials as a drug delivery system – a way to get drugs and medicines to where they are required in the body. The experiment with tea and the hydrogel is a model of this type of drug delivery system. The drug is first loaded onto the carrier and then it is released at the right location. The tea represents the drug and the hydrogel is the carrier.
Health & Safety checked, February 2008
session 7 supermolecules