Chemical Reactions

Overview

Most kids probably will have only covered chemistry at a very basic level, since elementary school science tends to concentrate on the "big picture." Therefore saying stuff like atoms and molecules will probably go way over their heads, especially the younger ones. However, some students should have had some basic chemistry or have had other units which overlap with it. Ideas like chemical properties or chemical reactions may not be so unfamiliar. The main goal of this lesson, then, is to demonstrate in a pretty graphic way different types of chemical reactions and what kinds of changes they can produce. Simple (and safe) reactions that produce heat, light, sound, etc. will be the focus.

Lead-in from last week and lead to the next lesson

Lukeís lesson should fit nicely into this one, since it focuses mainly on the demonstration of a couple of chemical reactions (the baking soda volcano and ice cream making).

The last portion of the lesson could focus on the catalase activity to show that chemical reactions are an integral part of all life, animals and plants.

Materials

fresh leaves

fresh liver

hydrogen peroxide

acetone

clear plastic cups

red cabbage

laundry ammonia

vinegar

flashlight

Questions

1. What is a chemical?

2. What is a chemical property?

3. What is a chemical reaction?

4. What can chemical reactions do?

5. Are there any chemical reactions going on in the human body?

Answering these questions is actually sort of difficult without referring to details like atoms or joules. There are a couple of important ideas to get across, one being the difference between chemical properties and physical properties. Instead of trying to give a definition of chemical properties, it will probably work better to give examples - specifically with the three planned activities. Emphasizing the idea that these reactions occur both in test tubes and in all living things may be interesting.

Young - The youngest students probably arenít going to understand anything and may not be able to give answers to any of question 2-5. You may have to lead them through the lecturish part and just get them to the demos and activities quickly so that they maintain interest. You probably should just try and make sure they have an idea of what a chemical property is and what the result of a chemical reaction might be.

Middle - These kids will probably pick up pretty quickly on concepts like properties. If you mention light as a possible product, theyíll probably be able to come up with things like heat, sound, cold, explosion, etc. You might want to go a little further into how these chemical reactions can be used by us (glow sticks, cold packs, etc.).

Older - You might be able to introduce some more advanced terminology like enzymes and catalysts, depending on the particular class. Some of the students might be familiar with atoms or even molecules so you might be able to launch into a bit more intricate explanation if they start asking questions.

Vocabulary

chemical

chemical reaction

chemical property

physical property

exothermic - A reaction that gives off heat. (eg. the catalase)

endothermic - A reaction that absorbs heat.

enzyme - A protein which catalyzes a particular reaction

chlorophyll

electron

indicator

acid

base

 

Demonstrations/Activities

Warnings: Most of the chemicals used in this demonstrations and activities are pretty volatile. Be careful when smelling them and MAKE SURE THE KIDS DONíT SMELL THEM DIRECTLY!!!! Nothing bad will happen, but nobody likes to get a big whiff of ammonia or ethanol in their face. Also, ethanol is an organic solvent, which means donít get it around your eyes if you wear contacts.

I. Mixtures and reactions (Demo)

The objective of this introductory portion is just to show that the kids shouldnít put too much reliance on their eyes. You should have three glasses filled half-way with water, vinegar, and ammonia respectively. You should also have an extract of red cabbage ready. Ask the kids to predict what will happen if you pour the extract that you are holding into the cup holding the water, without identifying the liquid. Repeat for the other two solutions. Vinegar contains acetic acid and ammonia is a base. For the kids that are a little older and a little more knowledgeable, you might ask for volunteers to come up and smell (wafting!) the three liquids.

 

II. Red Cabbage/vinegar/ammonia (activity)

The kids will work in groups of three or four on this. Each group should get a clear plastic cup with water and some shredded red cabbage leaves. They will basically be repeating the initial demonstration for themselves. It takes a little time for the extract to diffuse into the water (~20 minutes) so you probably want to set this up and then do the catalase activity in the meantime or the chlorophyll demonstration. After they have some extract ready give them each some vinegar to add. (Nothing so far is toxic). Ask them to add it and observe the color change. Next, give each group a little ammonia (this is bad so supervise them carefully). Add this to the mixture and again observe the color change. Note you will have a pretty large volume of liquid by this time so donít add too much vinegar or extract in the initial steps. If you do have too much, pour some out.

III. Glowing Chlorophyll (Demo)

Youíll need to get several leaves (nice healthy leafy ones), and find a way of boiling some ethanol. Boil the leaves in ethanol for a few minutes to extract the chlorophyll from them. Then turn out the lights and shine a blue light upon the extract directly. Electrons should be excited within the chlorophyll and give off a reddish light.

IV. Catalase (activity)

Hydrogen peroxide is pretty bad for the body and can damage tissues and cells pretty quickly. For this reason, animals have an enzyme called catalase which catalzyes the reaction of hydrogen peroxide into water and oxygen. The liver is a particularly concentrated source of catalase and produces a pretty neat reaction when mixed with hydrogen peroxide.

You will need to give each student a clear plastic cup. Have them place a ground-up piece of liver into their cup and then add a small amount of hydrogen peroxide (no more than a fourth of the cup). You should see some fizzing immediately. If you swirl the cup around gently, the fizzing will turn into pretty frantic bubbling (careful not to let it spill over). The cup should also feel warm to touch afterwards. The catalase reaction shows how a reaction can produce both gas and heat (exothermic).

Some kids are probably going to be finicky about touching liver. You should grind it up (just mushing it with your hands is good enough). If they simply wonít touch it, try breaking them up into groups where at least one person is willing.