Game Plan for Chemical Reactions

Monday May 31, 2010

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Objective You’re going to do several chemistry experiments that expose your kids to the different type of chemical reactions. I want you to focus on honing your observational skills when you do the experiments. Did the temperature, color or volume change? Even the smallest differences can indicate something big is going on. The first thing to do is watch the video on the Chemical Demonstrations website page, and then dive into the experiments.


Main Ideas Chemistry is chocked full of demonstrations and experiments for two big reasons. First, they’re fun. But more importantly, the reason we do experiments in chemistry is to hone your observational skills. Chemistry experiments really speak for themselves, much better than I can ever put into words or show you on a video. And I’m going to hit you with a lot of these chemistry demonstrations to help you develop your observing techniques.


While the kids are playing with the experiments see if you can get them to notice these important ideas. When they can explain these concepts back to you (in their own words or with demonstrations), you’ll know that they’ve mastered the lesson.


About the Experiments A lot of folks get nervous around chemistry. You can’t always ’see’ what’s going on (are there toxic gases generated from that reaction?), and many people have a certain level of fear around chemicals in general.


I don’t want you dipping your hands in molten lead or lying on a bed of nails while someone with a sledgehammer breaks a cinder block on your stomach. Demonstrations of this kind that result in injury are the ones forever burned in the memory of the audience, who are now fearful and have made the generalization that chemicals are dangerous and their effects are bad. In fact, every chemical is potentially harmful if not handled properly. That is why I’ve prepared a special set of chemistry experiments that include step-by-step demonstrations on how to properly handle the chemicals, use them in the experiment, and dispose of them when you’re finished.


Chemistry is predictable, just as dropping a ball from a height always hits the floor. Every time you add 1 teaspoon of baking soda to 1 cup of vinegar, you get the same reaction. It doesn’t simply stop working one time and explode the next. I’m going to walk you through every step of the way, and leave you to observe the reactions and write down what you notice. At first, it’s going to seem like a lot of disjointed ideas floating around, but after awhile, you’ll start to see patterns in the way chemicals interact with each other. Keep working at Chemistry and eventually it will click into place. And if there’s an experiment you don’t want to do, just skip it (or just watch the video). Some of this may be a review for you, especially if you’ve completed Units 3 (Matter) and 8 (Chemistry 1).


The How and Why Explanation There are several different types of chemical reactions: combustion, decomposition, synthesis, and displacement. All chemical reactions somehow fit into one of these, and here’s how you can tell them apart…


Combustion: A combustion reaction gives off energy, usually in the form of heat and light.  The reaction itself includes oxygen combining with another compound to form water, carbon dioxide, and other products. A campfire is an example of wood and oxygen combining to create ash, smoke, and other gases.


Synthesis: This reaction happens when simple compounds come together to form a more complicated compound. The iron (Fe) in a nail combines with oxygen (O2) to form rust, also called iron oxide (Fe2O3).


Oxidation-Reduction (Redox Reaction): When the oxidation numbers of atoms change during the reaction, it’s called a redox reaction. Oxidation happens when a compound loses electrons (increases oxidation state) and reduction occurs when a compound gains electrons (decrease in oxidation state). Electroplating is an example of a redox reaction.


Decomposition: On the other side, a decomposition reaction breaks a complicated molecule into simpler ones. When you leave a bottle of hydrogen peroxide on the counter, it decomposes into water (H2O) and oxygen (O2).


Displacement: There are several different types of displacement reactions, including single, double, and acid-base more on this later). Antacids like calcium hydroxide (CaOH) combine with stomach acid (HCl) to form calcium chloride salt (CaCl2) and water (H2O).


Questions to Ask When you’ve worked through most of the experiments ask your kids these questions and see how they do:


  1. What’s true about phenolphthalein? (a) it goes from clear to pink when mixed with bases (b) it’s impossible to spell (c) it is colorless in acidic solutions (d) soluble in water
  2. How does increasing the hydrogen peroxide affect the rate of the iodine clock reaction?
  3. Which chemical turns coldest when added to water? (a) calcium chloride (b) aluminum sulfate (c) ammonium nitrate (d) citric acid
  4. A polymer is: (a) a long piece of spaghetti (b) an element on the periodic table (c) a long molecular chain (d) a plastic bag
  5. What does a cross-linking agent do?
  6. Which of the following are cross-linking agents? (a) calcium (b) borax (c) white glue (d) starch (e) bubble gum
  7. Which substance is both a solid and a liquid? (a) bubble gum (b) slime (c) cornstarch and water (d) last night’s dinner

Answers:


  1. What’s true about phenolphthalein? (a) it goes from clear to pink when mixed with bases (b) it’s impossible to spell (c) it is colorless in acidic solutions (d) soluble in water
  2. How does increasing the hydrogen peroxide affect the rate of the iodine clock reaction? By accelerating the first reaction, you can shorten the time it takes the solution to change color. There are a few ways to do this: You can decrease the pH (increasing H+ concentration), or increase the iodide or hydrogen peroxide. (To lengthen the time delay, add more sodium thiosulfate.)
  3. Which chemical turns coldest when added to water? (a) calcium chloride (b) aluminum sulfate (c) ammonium nitrate (d) citric acid
  4. A polymer is: (a) a long piece of spaghetti (b) an element on the periodic table (c) a long molecular chain (d) a plastic bag
  5. What does a cross-linking agent do? Coagulates the polymers. (Turns the long polymer chains into something that looks more like a fishnet.)
  6. Which of the following are cross-linking agents? (a) calcium (b) borax (c) white glue (d) starch (e) bubble gum
  7. Which substance is both a solid and a liquid? (a) bubble gum (b) slime (c) cornstarch and water (d) last night’s dinner

Game Plan for Slime Science

Monday May 31, 2010

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Objective When you think of slime, do you imagine slugs, snails, and puppy kisses? Or does the science fiction film The Blob come to mind? Any way you picture it, slime is definitely slippery, slithery, and just plain icky — and a perfect forum for learning real science.


Imagine a plate of spaghetti. The noodles slide around and don’t clump together, just like the long chains of molecules (called polymers) that make up slime. They slide around without getting tangled up. The pasta by itself (fresh from the boiling water) doesn’t hold together until you put the sauce on.  Slime works the same way. Long, spaghetti-like chains of molecules don’t clump together until you add the sauce … until you add something to cross-link the molecule strands together.


About the Experiment To make our different slimes, we’ll be using borax as the cross-linking agent.  There a lots of different polymers you can try, including starch, glue, and polyvinyl alcohol.  The polymer (usually glue) mixture is the “spaghetti” (the long chain of molecules), and the “sauce” is the borax mixture (the cross-linking agent).  You need both in order to create slime. Keep your slime in the fridge for a week, or a month in the freezer (although it might change colors). Nuke it in the microwave for a few seconds to thaw.


The How and Why Explanation The cross-linking agent in the slime mixtures can be either liquid starch or borax (sodium tetraborate).  When you mix the glue and water together, you’ve got a cup full of long molecule chains, like a pile of ropes.  When you cross-link the polymers, it’s like building a net with the rope, and it happens very quickly to give you that rubbery, stretchy substance kids are so fond of.


Questions to Ask When you’ve worked through most of the experiments ask your kids these questions and see how they do:


  1. A polymer is: (a) a long piece of spaghetti  (b) an element on the periodic table (c) a long molecular chain (d) a plastic bag
  2. What does a cross-linking agent do?
  3. Which of the following are cross-linking agents?  (a) calcium  (b) borax  (c) white glue    (d) starch  (e) guar gum
  4. What does PVA stand for?  What kind of water does it mix with?
  5. Which substance is both a solid and a liquid?  (a) guar gum  (b) bouncy putty (c) starch slime (d) corny slime

Swamp Muck Science Game Plan

Monday May 31, 2010

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Objective This experiment will teach you about the different types of filtration as you turn your coffee back into clear water as well as the swamp muck from the back yard.   You can test out other types of “swamp muck” by mixing together other liquids (water, orange juice, etc.) and solids (citrus pulp, dirt, etc.).  Stay away from carrot juice, grape juice, and beets — they won’t work with this type of filter.


About the Experiment Ever wonder how the water draining down your sink gets clean again? Think about it: The water you use to clean your dishes is the same water that runs through the toilet.  There is only one water pipe to the house, and that source provides water for the dishwasher, tub, sink, washing machine, toilet, fish tank, and water filter on the front of your fridge.  And there’s only one drain from your house, too!  How can you be sure what’s in the water you’re using?


In our live Science Camp Workshops during the summer, we let the kids bring in their own samples which usually includes a blenderized version of leftovers from dinner, plant trimmings, coffee grounds, and dirt. It’s quite a smelly class once everyone cracks open their samples!


The How and Why Explanation There are several steps to understand as we go along:


  • Aeration:  Aerate water to release the trapped gas.  You do this in the experiment by pouring the water from one cup to another.
  • Coagulation: Alum collects small dirt particles, forming larger, sticky particles called floc.
  • Sedimentation: The larger floc particles settle to the bottom of the cup.
  • Filtration:  The smaller floc particles are trapped in the layer of sand and cotton.
  • Disinfection:  A small amount of disinfectant is added to kill the remaining bacteria.  This is for informational purposes only — we won’t be doing it in this experiment.

Questions to Ask When you’ve worked through most of the experiments ask your kids these questions and see how they do:


  1. What is the alum used for in the water filtration experiment? (a) to adjust the pH  (b) to form floc (c) to float to the top (d) to purify the sample
  2. What does the activated carbon do? (a) turns the cotton balls black   (b) sinks the floc  (c) adjusts the pH (d) adds to the filtering power of the cotton (e) none of the above (f) all of the above
  3. Draw a sketch of your filter, labeling the different layers.

Game Plan for Bubblology

Sunday May 30, 2010
Magician Tom Noody

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Objective If you’re fascinated by the simple complexity of the standard soap bubble, then this is the lab for you.  You can easily transform these ideas into a block-party Bubble Festival, or just have extra fun in the nightly bathtub.  Either way, your kids will not only learn about the science of water, molecules, and surface tension, they’ll also leave this lab cleaner than they started (which is highly unusually for science experiments!)


About the Experiments The absolute best time to make gigantic bubbles is on an overcast day, right after it rains.  Bubbles have a thin cell wall that evaporates quickly in direct sun, especially on a low-humidity day.  If you live in a dry area with low-humidity, be sure to use glycerin. The glycerin will add moisture and deter the rapid thinning of the bubble’s cell wall (which cause bubbles to tear and pop).


The How and Why Explanation If you pour a few droplets of water onto a sweater or fabric, you’ll notice that the water will just sit there on the surface in a ball (or oval, if the drop is large enough).  If you touch the ball of water with a soapy finger, the ball disappears into the fibers of the fabric!  What happened?


Soap makes water “wetter” by breaking down the water’s surface tension by about two-thirds.  Surface tension is the force that keeps the water droplet in a sphere shape.  It’s the reason you can fill a cup of water past the brim without it spilling over. Without soap, water can’t get into the fibers of your clothes to get them clean. That’s why you need soap in the washing machine.


Soap also makes water stretchy. If you’ve ever tried making bubbles with your mouth just using spit, you know that you can’t get the larger, fist-sized spit bubbles to form completely and detach to float away in the air. Spit is 94% water, and water by itself has too much surface tension, too many forces holding the molecules together.  When you add soap to it, they relax a bit and stretch out.  Soap makes water stretch and form into a bubble.


The soap molecule looks a lot like a snake; it’s a long chain that has two very different ends.  The head of the snake loves water, and the tail loves dirt.  When the soap molecule finds a dirt particle, it wraps its tail around the dirt and holds it.


The different colors of a soap bubble come from how the white light bounces off the bubble into your eye. Some of the light bounces off the top surface of the bubble and bends only a little bit, while the rest passes through the thin film and bounces off the inner surface of the bubble and refracts more.


If you made the Hover Bubbles, you’ll notice that the bubbles slowly get larger the longer they live in the tank.  Remember that the bubble is surrounded by CO2 gas as it sinks. The bubble grows because carbon dioxide seeps through the bubble film faster than the air seeps out, as CO2 is more soluble in water than air (meaning that CO2 mixes more easily with water than air does).


Questions to Ask


  1. Which soap solution makes the biggest bubbles?
  2. Does water temperature matter?
  3. How would you make a square bubble?
  4. Why can you poke a straw through a bubble after it’s been dipped in bubble solution?