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I made ScienceFix.com to share my favorite demos that I do in my middle school science classes.  

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Saturday
Jun202009

Video Demo: Flame Tests

Every chemical has its unique characteristic properties. These properties can include hardness, density, melting point, boiling point, color, taste, texture etc. No matter what sample you have of a pure substance they will display its characteristic properties. This is how a an unknown chemical can be identified. The properties of the unknown chemical can be compared to the properties of known chemicals. In this activity there are 3 unknown chemicals (X, Y, and Z) that are to be identified based on 5 properties: color, boiling point, melting point, density, and color when burned. This is a simple and quick lab activity. The handout has the density, boiling point, and melting point filled in already. The students must observe the color and the color when burned–a flame test. Slide 1 shows the materials needed for the activity (the 3 chemicals are copper sulfate, strontium chloride, and lithium chloride). Slide 2 shows the Bunsen burner flame with the typical blue color. Slide 3 shows the inoculating loop collecting some of chemical Y. When the different chemicals are put in the flame, they burn at different colors (Slide 4 shows copper sulfate’s green flame, and slide 5 shows lithium chloride’s red flame).

Tips: Make sure students are careful to not contaminate the tubes and to thoroughly clean loop before testing each chemical.

Safety: Make sure students wear goggles, and know how to properly use a Bunsen burner safely.

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This is a variation on the flame test lab. Instead of using a Bunsen burner, a denatured alcohol flame is used (the best results is achieved by using methanol). Put a spoonful of strontium chloride into a Pyrex petri dish (this glass can take the heat, any other non Pyrex glass will break). Put about 2-3 spoonfuls of denatured alcohol into the dish. Swirl around to mix. Carefully light the alcohol on fire. You will probably need to swirl it so that the strontium chloride will burn and produce the red flame (lower left image). Try this with other salts and compounds that are safe to burn and will give color (like copper sulfate–lower right image).

ultra flame test materials

ultra flame test red ultra flame test green

 

Precautions: ONLY TEACHER DEMO! Be sure to use only Pyrex petri dish. The dish will get very hot! Don’t let water hit it right away. Be sure to blow flame out.

Friday
Jun192009

Video Demo: Muscle Pair

Seventh graders in the state of California are required to learn how bones move. Of course bones move because skeletal muscles are attached to bones, and when they contract, they make a bone move in one direction. Muscle work in pairs and when one muscle contracts, the other relaxes. Below are two video demos that show students how the biceps/triceps muscle pair works together to move the radius/ulna.

The first video is a model of how the biceps/triceps muscle pair works. In the model the radius/ulna and the humerus are represented by meter sticks. The meter sticks meet at a point which represents the joint (in this case a hinge joint). A joint is where two bones meet. The muscles in the video are represented by white irrigation tubing. The tubing is attached to each bone via duct tape. The duct tape represents a tendon. Tendons are connective tissue that connects muscles to bone. When the irrigation tubing (muscle) contracts, gets shorter, it moves the radius/ulna in a certain direction. When one muscle contracts, the other muscle relaxes.

The second video demonstrates the triceps/biceps muscle pair at work in a chicken wing. The video demonstrates how to dissect the chicken wing and then what happens to the radius/ulna when the biceps contract and then when the triceps contract. If students do the chicken wing dissection, make sure that proper washing and disposal precautions are taken so as to prevent biocontamination. If anyone is interested in a student worksheet email me at sciencefix@gmail.com and put “chicken wing dissection handout” in the subject line. I will then send you a copy.

Thursday
Jun182009

Video Demo: Grain Silo Explosion

BubbleShare: Share photos - Easy Photo Sharing This is a very popular demo in science classes around the country. You need a coffee can with lid, candle, and irrigation tubing (slide 1). You can use cake flour, corn starch, or lycopodium powder. Put some of the substance into a petri dish. Light a match and place the flame next to the substance. The substance will brown but it won’t ignite. Place the substance into the coffee can next to the tube (use a drill to make a hole near the bottom of the can so the tube can fit). Light a candle (the best kind are the flat votive kind) and place it opposite the hole (slide 2). Put the lid on the can and make sure it is snugly fit. Take in a deep breath, then place the tube into your mouth and exhale a big breath. An small explosion will happen causing the lid to fly off. This demo demonstrates that for a substance to ignite it needs oxygen. When the substance is packed together there isn’t enough oxygen that surrounds the particles and ignition can’t occur. By blowing into the can the substance spreads apart, increasing the surface area, causing the ignition and the reaction happens very quickly.

Precautions: Wear goggles. Try this demo ahead of time to make sure it works safely. Make sure students are at a safe distance.

 

Wednesday
Jun172009

Demo: Gold Penny

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This is not so much a lesson but rather a demo. This is kind of a “Wow!” demo. The chemical composition of the penny has varied greatly through the years. From 1793 to 1837 it was actually pure carbon. It went through many changes since then. From 1864 to 1962 it was bronze (95 percent copper, 5 percent zinc and tin). In 1962 the penny’s tin content was removed, which made it 95 percent copper and 5 percent zinc. In 1982, the composition changed to 97.5 zinc and 2.5 percent copper (copper plated zinc). In this demo you need pre 1982 pennies (The US Mint has a good slideshow on how coins are made). The purpose of this demo is to give the penny a zinc plating, then heat it up to form a brass alloy so that it will look like gold. You can discuss in this demo the various properties of metals. Also you can discuss the technique of wet chemical plating, a technique first discovered by alchemist centuries ago, to try to fool people into believing they had the ability to change common metals into precious metals. This demo was taken from the Chemistry Demo a Day book.

Procedure:
1. Get the materials as shown in slide 1.
2. Mix about 24 g of sodium hydroxide into 200 ml of water. Use a 400 ml beaker. Heat the mixture on a medium low setting. Do not boil.
3. Mix in 5 g of granular zinc. (slide 2)
4. Place penny into beaker and stir for about 4 minutes (slide 3).
5. Use tongs to take out penny and place in water (slide 4). This stops the process. Rub penny with cloth to create a sheen. The penny is now zinc plated. It kind of looks like a silver penny (slide 6)
6. Use tongs to slowly heat penny over a Bunsen burner flame. Slowly move the penny back and forth across the flame. The heat makes the zinc atoms mix with the copper atoms to form a brass alloy. It looks kind of like gold (slide 6).
Tips: Have a student assistant help you with the procedure. They will have fun. Have pennies that have already been done, to pass out to students during the demo so they can have an up close look.

Tips: Have a student assistant help you with the procedure. They will have fun. Have pennies that have already been done, to pass out to students during the demo so they can have an up close look.

Safety: Make sure you and the student wear goggles, and know how to properly use a Bunsen burner safely. Make sure room is well ventilated.

Tuesday
Jun162009

Solar System Scale Model Tour

When students learn about the Solar System they have a difficult time visualizing or comprehending what the distances are like between the planets and the sizes of the planets and the Sun. Most textbooks show pictures of the planet on one scale and the distances between the planets on another scale. They never have them to the same scale. The reason why is that the Solar System is huge! There are a ton of Solar System scale model lessons on the web. One of the best is the half mile long model. In this model the following represent the planets (see slide show): Mercury, Mars, and Pluto = head of pin, Earth and Mars = peppercorn, Jupiter = rubber ball, Saturn = hazelnut, Uranus and Neptune = peanut, Sun = volleyball. I glued these items (except the volleyball) to paper plates. I then made a flag for each planet out of wooden dowels and construction paper. I then inserted the flags through the middle of the paper plates and set the combination into a PE cone (see slide show). The distance between the planets are on the teacher handout (students have a separate handout). I have my students record into a lab composition book a journal of their tour. They answer questions before, during and after the tour. They are pretty amazed by the size of the model (see slide show). You need to have a pretty straight stretch of street (see slide show) to use, that isn’t too busy. I give my principal notice ahead of time and I also bring a first aid kit.

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