ChemShorts for Kids   --   2007
Copyright ^©2007 by the Chicago Section of the American Chemical Society

Please note:  All chemicals and experiments can entail an element of risk, and no experiments should be performed without proper adult supervision.

Kids, what causes the “smoke” from bubbling beakers and flasks in TV shows and movies?  Dry ice is another name for the solid form of carbon dioxide (CO₂).  It is colder than water ice but can be handled safely for short periods of time with insulating gloves. There is a video of the classic dry ice fog demonstration on-line (at http://www.metacafe.com/watch/286601/dry_ice/ ), with a twist.  After water is added to the dry ice to create a smoky fog, hand soap is squirted into the mix.  The resulting cascade of bubbles is fun, but what makes this video really interesting is the bubbles vanishing in a puff of fog when touched.

To try this at home, we recommend an adult partner only for handling the dry ice, using tongs and insulating gloves (such as leather gardening gloves). A double Styrofoam cup makes a good container, and we suggest putting this inside a secondary container (like a dishpan, for example).  A ceramic coffee cup would probably also work.  A single large chunk of dry ice will last longer than a number of smaller chunks, and hot water works better than cold, but just use hot water from the tap.  Boiling hot water could create a hazard in handling.

Dry ice is so called because it does not melt into liquid carbon dioxide before turning into gas. The process of a liquid changing state into gas is called evaporation. When a solid changes directly into gas, the process is called sublimation.

The white cloud that forms is not smoke, but rather condensed water vapor. Tiny droplets of water make the white cloud. The clouds almost immediately disappear because the water droplets warm right back up and re-evaporate back to form invisible water vapor. This is how fog forms: when it is humid enough and the temperature drops enough you get lots of tiny water droplets forming.

Notes

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Reference:

Dr. Anne Marie Helmenstine at
http://chemistry.about.com/library/weekly/aa010603a.htm  
http://chemistry.about.com/b/a/257641.htm
http://chemistry.about.com/cs/howtos/ht/nontoxicsmoke.htm

Kids, did you know that whipping eggwhites in a copper bowl gives different results from beating them in a glass, ceramic, or steel bowl? One common technique used in baking is to whisk egg whites in order to make especially light, airy or fluffy delicacies. When air is whisked into egg whites, the mechanical action starts to “unfold” the proteins in the whites. The scientific term for this is to “denature”. The denatured proteins begin to stick together, (or “coagulate”), stiffening the foam and stabilizing the air bubbles. If the foam is overbeaten in a non-copper bowl, eventually the proteins become completely denatured and coagulate into clumps. This is not a good thing.

In turns out that, in copper bowls, the eggwhites react with the metal in the bowl to produce a complex that gives the egg whites a golden color. Some copper ions migrate from the bowl into the egg whites. They become harder to overbeat and give long-lasting “peaks” (a cooking term used to describe shapes that can stand on their own) . Copper bowls produce a yellowish, creamy foam that is harder to overbeat that the foam produced using glass or stainless steel bowls. The copper ions form a yellow complex with one of the proteins in eggs, conalbumin. The conalbumin-copper complex is more stable than the conalbumin alone, so egg whites whipped in a copper bowl are less likely to denature (unfold).

If a copper bowl is used, then fewer protein molecules are free to denature and coagulate, because some are tied up in conalbumin-copper complexes. In addition to forming complexes with conalbumin, the copper may also react with sulfur-containing groups on other proteins, further stabilizing the egg proteins. Although the iron and zinc found in other metal bowls also form complexes with conalbumin, these complexes don't make the foam more stable. When glass or steel bowls are used, cream of tartar may be added to egg whites to stabilize the whites.

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Reference:

Dr. Anne Marie Helmenstine at 
http://chemistry.about.com/od/howthingsworkfaqs/f/copperbowl.htm

Alka-Seltzer Surface Area

Kids, did you know that the rate of a chemical reaction can be affected by the physical size of the reactants?   When decreasing the size of particles that weigh a certain amount, you will increase the number of particles.  Here you will test the hypothesis that smaller particle size can increase the rate of a reaction because the surface area of the reactant has been increased.  Before beginning, make a prediction that a powdered form of a tablet will react X times faster than a whole tablet (guess at X).

You will need: 3 clear glasses, 3 Alka-Seltzer® tablets (original formula effervescent), a mortar and pestle, and a stopwatch. Here is the procedure:

1. Whole Tablet
   a. Fill a clear glass with exactly 8 oz. of room temperature or lukewarm water.
   b. Drop 1 whole Alka-Seltzer tablet into the water. Measure and record the time to dissolve.
2. Tablet Broken into ~8 Pieces
   a. Place 1 Alka-Seltzer tablet onto a sheet of paper and break into approximately 8 pieces of about equal size.
   b. Fill a clear glass with exactly 8 oz. of room temperature or lukewarm water.
   c. Slide broken tablet into the water from the sheet. Measure and record the time to dissolve.
3. Powdered Tablet
   a. Place 1 Alka-Seltzer tablet into mortar and grind to a fine powder.
   b. Transfer powder into a clear cup. (Note: It's important to have the powder in the cup before adding water.)
   c. Add 8 oz. of water to the glass. Measure and record the time to dissolve.

From your measurements, determine whether the rate of reaction increased or decreased as the particle size decreased, and by how much. Was is 2 times faster, or more?

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Reference:
http://www.alka-seltzer.com/asp/student_experiments_2.html

Reaction Rates

Kids, do you think that temperature will have an affect on how fast or slow a reaction might take place?  In order for a chemical reaction to occur, the molecules, which are REACTANTS, must physically come into contact with one another. Anything that increases the frequency of these encounters will increase the rate at which PRODUCTS are formed. Your hypothesis can be that the rate of a chemical reaction will be increased by raising the temperature of reactants.

You will need: 6 clear cups, a measuring cup, a thermometer (-20° C to 110° C), 3 original formula effervescent Alka-Seltzer® tablets, a stopwatch, a mortar and pestle, a source of hot water, ice cubes, and graph paper.

Procedure—  Run water from the hot tap until it is as hot as possible. Fill a clear glass with exactly 8 oz. of hot water. Use the thermometer to take the temperature and record it on a data sheet. Drop 1 Alka-Seltzer® tablet into water. Measure the time required for the tablet to fully dissolve. Be prepared to start and stop on time. The reaction will take less than 15 seconds. Record the time. Repeat this experiment using room temperature water.

For the cold water test, the procedure is a little different. Fill a clear glass with 4 oz. of water and add enough ice to adjust the level to 8 oz. Stir the ice water for about 15 seconds so the temperature will come to equilibrium. Use the thermometer to take the temperature and record it on your data sheet. (Leave the ice cubes in the water!) Drop 1 Alka-Seltzer tablet into the water. Measure and record the time required for the reaction to be completed.

Analysis—  Graph your data points (water temperature vs. time to fully dissolve) to show the effect of temperature on Rate of Reaction.

So now can you answer this question? As the temperature increases, the rate of reaction increases, decreases, or stays the same? How about these more advanced questions?

1. At a temperature of 10 degrees C, it would take ______ seconds for 1 Alka-Seltzer tablet to react with 8 oz. of water.
2. If the temperature is doubled from 20 degrees C to 40 degrees C, the time for the rate of reaction ______by approximately _______.
3. Using hot tap water, the rate was ______ times faster than at 0 degrees C.

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Reference:
http://www.alka-seltzer.com/asp/student_experiments_1.html

Homemade Floam

Kids, what is like slime with polystyrene beads in it that can be molded into shapes? It’s a really fun toy called Floam™. You can sculpt with this colorful goop or use it to coat other objects. You can store it to reuse it or allow it to dry, if you want permanent creations. It's a lot of fun, but not always easy to locate. So, you can make a type of 'Floam' yourself. Like slime, it is generally safe, though anything containing food coloring can stain surfaces (don’t eat it though, because polystyrene beads simply aren't food!).

Here is what to do:

1. Dissolve 2 tsp. borax completely in 1/2 cup water. (If you want slimier, more flexible 'Floam', then try 1 tsp. borax instead)

2. In a separate container, mix 1/4 cup white glue and 1/4 cup water. Stir in food coloring.

3. Pour the glue solution and about 1 1/3 cup of polystyrene beads into a Ziploc^® plastic bag. Add borax solution and knead it until it's well mixed. Use 1 tbsp. of the borax solution for a very fluid Floam, 3 tbsp for average Floam, and the entire amount for stiff Floam.

4. To keep your Floam, store it in a sealed bag in the refrigerator (this discourages mold). Otherwise, you can allow it to dry into whatever shape you chose.

How it works:

Borax reacts to crosslink the polyvinyl acetate molecules in the glue. This forms a flexible polymer.

Tips:

1. If you use a 4% solution of polyvinyl alcohol instead of glue, you will get a more transparent product that will hold shapes better.

2. Polystyrene beads can be found at craft stores (e.g., JoAnn Fabrics), usually as fillers for bean bags or dolls. Or, for more hands on fun, you can grind Styrofoam™ cups using a cheese grater.

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Reference:

Super Sorting Challenge

Kids, how do you think recyclers separate all that stuff they get in their bins?  Materials can be grouped or separated by how they look and/or by the material of which they are made.  These qualities are called properties of the materials.  Some recyclers use special properties of materials to group recyclables.  In this activity, you will separate materials based on their special properties.

You will need: a magnet, a plastic straw or coffee stirrer, blunt-end scissors, metric ruler, 1 latex balloon, 1 square of aluminum foil (5 x 5 centimeters), 1 square of paper towel (5 x 5 centimeters, cm), 5 small metal paper clips, 1 piece of window screening (20 x 30 cm), and a rectangular cake pan (about 32 x 23 x 5 cm).

Here is what to do:

1. Cut the plastic straw into five pieces (any size) using the scissors.
2. Cut or tear the aluminum foil and the paper towel into 5 pieces each (any size).
3. Roll each piece of paper towel into a ball between your thumb and index finger.
4. Place the pieces of straw, aluminum foil, paper towel, and the paper clips together in a pile on the screen.
5. Move the magnet through the pile (you may need to bring it very close to the objects). Put any objects picked up by the magnet aside in a pile. Record the objects picked up.
6. Inflate the balloon and tie it closed (your adult lab partner may need to help you). Rub the balloon back and forth on your hair. Hold the balloon close to the pile and see what happens to the objects. Put everything that is attracted to the balloon in a second pile. Record these items.
7. Now fill the cake pan with water. Take the screen with the remaining objects on it and dip it into the water so that the screen touches the bottom of the pan. Pick off any floating materials and put them in a third pile. Record these items.
8. Now lift the screen and put the remaining objects in a fourth pile. Record these items.
9. Thoroughly clean the work area and wash your hands.

Where’s the Chemistry?  Materials have different chemical and physical properties that make them easy to separate. Recycling plants use machines that vibrate to sort paper from wood and cardboard. They use magnets to pull out tin and steel that is mixed with aluminum and plastic. Paper, glass, plastic, and metal each has its own chemical make-up and its own way of being recycled. It is important that each is separated from the other items before recycling. Paper is cut up, bleached and pulped. Some metals can be picked up by magnets and other metals cannot. Some materials are attracted to each other because of static electricity, which involves positive and negative charges. The hollow plastic straw pieces float because they spread their weight out and can float on the water’s “skin.” This skin forms because water tends to stick to itself, which is called cohesion. Materials with properties that are alike get cleaned, cut up, melted down and then made into new products. Some recycling plants are starting to use these different properties to help them sort out materials. They make machines to separate out recyclable materials just like you did but their process is on bigger scale!

Be sure to do this activity with an adult!  Reuse/recycle as many of the materials as possible!  Check your reuse/recycle plans with your adult lab partner first.

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Reference:

American Chemical Society’s website for kids, see “Milli’s Super Sorting Challenge", at:
http://acswebcontent.acs.org/celebrate_chemistry/2007/MillisSortingChallenge.pdf

Static Power

Kids, can you imagine being able to bend water with static electricity? When two objects are rubbed against each other, some of the electrons from one object can jump to the other. The object that gains electrons becomes more negatively charged; the one that loses electrons becomes more positively charged. The opposite charges attract each other in a way that you can actually see.

One way to collect charge is to comb your hair with a nylon comb or rub it with a balloon. The comb or balloon will become attracted to your hair, while the strands of your hair (all the same charge) repel each other. The comb or balloon will also attract a stream of water, believe it or not, because the water stream carries an electrical charge.

Here is what to do:

1. Comb dry hair with a nylon comb or rub it with an inflated latex balloon.
2. Turn on the tap so that a narrow stream of water is flowing (1-2 mm across, flowing smoothly).
3. Move the balloon or side of the comb close to the water (not in it). As you approach the water, the stream will begin to slightly bend.

Experiments: It is fun to test these questions and try these variations. Does the amount of 'bend' depend on how close the comb is to the water? If you adjust the flow, does it affect how much the stream bends? Do combs made from other materials work equally well? How does a comb compare with a balloon? Do you get the same effect from everyone's hair or does some hair release more charge than others? Can you get your hair close enough to the water to repel it without getting it wet?

Tip: This activity works better when the humidity is low. When humidity is high, water vapor catches some of the electrons that would jump between objects. For the same reason, your hair needs to be completely dry when you comb it.

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Reference: 
Anne Marie Helmenstine at http://chemistry.about.com/od/chemistryexperiments/ht/bendwater.htm

A Chemistry Scavenger Hunt

Kids, tell your teacher that you would like your class to do a chemistry scavenger hunt! These are really popular assignments where students are asked to identify or bring in items that fit a description. Examples of scavenger hunt items are below. Many of these topics have been tackled in our previous 150+ columns. A partial list of possible “answers” to 5 items is also provided – you can find more at the website below.

First, start with the clues. Find:

1. An element
2. A heterogeneous mixture
3. A homogenous mixture
4. A gas-liquid solution
5. A malleable substance
6. A solid-liquid solution
7. A substance that has a volume of 1 cm3
8. An edible example of a physical change
9. An edible example of a chemical change
10. A pure compound containing ionic bonds
11. A pure compound with covalent bonds
12. A mixture that can be separated by filtration
13. A substance with a density less than 1g/mL
14. A substance with a density more than one
15. An acid
16. A metal
17. A non-metal
18. Immiscible liquids
19. A base with a pH greater than 9
20. A polymer

Sample answers:

1. aluminum foil, copper wire, aluminum can, iron nail

4. a soda

5. play-doh or modeling clay

7. sugar cube

8. melting ice cream

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Reference: Anne Marie Helmenstine
at http://chemistry.about.com/od/chemistry101/a/scavenger.htm

Thermometer Thoughts

Kids, how would you like to make your own thermometer? All you will need is some water, rubbing alcohol, a clear, narrow-necked plastic bottle, food coloring, a clear plastic straw, and tape or modeling clay. Here is what you do:

1. Pour equal volumes of rubbing alcohol and water into the bottle. You want the bottle to be at most 1/4 full.
2. Add a couple drops food coloring.
3. Put the straw in the bottle such that the bottom is under the liquid, but not touching the bottom of the bottle.
4. Fix the straw in place using tape or clay. Seal the bottle so that air can not get in or out of the bottle around the straw.
5. Heat the bottle and watch what happens. The easier way is to hold it in your hands for a few minutes.
6. You can cool the bottle by putting it in the fridge.

Congratulations - you just made a thermometer! Just like any thermometer, the liquid expands when warmed. This makes the liquid no longer fit in the bottom of the bottle. As the alcohol expands the colored mixture moves up through the straw. You can watch your thermometer and see how the liquid changes throughout the day. What happens if your thermometer is in shadow or in sunlight? The liquid should go up the straw with heat and down the straw when cooled (hopefully not all the way or the thermometer might not work anymore).

Why does the level of the liquid change with temperature? Because the air in the bottle changes volume with temperature. As air is heated it either expands or exerts more pressure. In trying to expand and in exerting pressure, it fights gravity and pushes some liquid up the straw. Most common thermometers work with exactly these principles.

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Reference:

http://www.energyquest.ca.gov/projects/thermometer.html   and
http://experimentopia.org/experiment/build_your_own_thermometer

Mustard Mystery

Kids, is there really silver in that silver coin?  Even though our dimes, quarters, half dollars, and "silver" dollars are silver in appearance, those minted after 1971 actually have no silver in them. Silver was completely removed from dimes and quarters in 1965 and replaced with an outer layer of copper-nickel alloy bonded to an inner core of pure copper. The half dollar and "silver dollar" followed suit in 1971.  Believe it or not, our "copper" pennies nowadays are mostly zinc and our "silver" coins are mostly copper!

Dimes and quarters minted before 1965 were composed of an alloy of 90% silver and 10% copper, and they are considered somewhat valuable by collectors. You can easily test for the presence of silver with a simple experiment. Using a plastic knife, apply a generous portion of mustard (yes, the yellow stuff you put on your hotdog) to both pre-1965 and post-1965 dimes and quarters. Let them sit overnight on a paper towel. The next day, rub off the mustard. A black spot will remain on the true silver coin but not on a non-silver coin.

What's happening? Mustard contains natural sulfur compounds. Sulfur is an element that is very common in our day-to-day world. Sulfur reacts with the silver to form a black powder (a "precipitate") of silver sulfide. The chemical formula for silver sulfide is Ag₂S. One of the challenges for this experiment will be in hunting down the pre-1965 coins - good luck and happy hunting!

Here is an interesting tidbit. Eggs also contain a lot of sulfur. If you eat eggs with a silver plated fork you will find that your fork has black tarnish on it when you are finished. You made a new chemical while eating your breakfast!

Check out the ChemShorts October 2000 article on "The Science of Money" for other interesting trivia about coins and paper money (http://membership.acs.org/C/Chicago/ChmShort/CS00.html#10.00).

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References:

Brian Rohrig, "The captivating chemistry of coins", ChemMatters, ACS publication, April 2007, page 14 and
On-line Museum Educators at http://www.fi.edu/pieces/knox/mustardtrick.htm