Reaction Bag

This is a lesson that I got from another teacher, who I think got it from Science Gems. My eighth graders have to learn what chemical reactions are and how to recognize them. Our textbook describes 5 types of evidence that a chemical occurred. They are color change, temperature change, gas production, precipitation and change in properties (like smell , taste, texture, etc.). In this lesson students have to look for which types of evidence occur when calcium chloride, sodium bicarbonate, and phenol red solution are mixed together. What is really cool about this lesson is that students get to feel the reaction. The chemical reaction takes place in a sealed plastic bag. It inflates because carbon dioxide gas is produced, it gets very hot, it changes from a red color to a yellow color (the carbon dioxide makes the liquid acidic), and the smell at the end is a chalk smell (calcium carbonate). Download the student handout and view the quicktime video (or Google Video) and pictures on how the lesson works.

Materials needed

Tips: Emphasize to the students to feel the solid chemicals immediately after all chemicals are mixed together so they are able to sense the temperature change.

The Reverse Balloon

One of my all time favorite demos. This is a variation on the crushing of the soda can via atmospheric pressure. I do this demo when studying the phases of matter. The molecules in a gas are rapidly moving in all directions and they are spaced as far apart as possible. When cooled to a liquid phase, the molecules come together as close together as possible thus taking up less space. This demo illustrates that.

Fill the 250 ml flask with about 50 ml of water. Set the flask on the hot plate and heat until water boils. Carefully take the flask off the hot plate with tongs. Carefully (don’t get burned) stretch the opening of the balloon over the mouth of the flask. Then with tongs, carefully transfer the flask so that the bottom half sits in ice water. Watch what happens!

The gaseous water in the flask quickly turns to the liquid phase. The molecules in the liquid phase take up much less space (volume) and the balloon gets pushed (sucked) into the flask and stays that way. Your students will be amazed.

Sometimes I show the end result to them first, and they are then challenged to test ways in which it can be done.

Precautions: Use tongs in this demo. The flask gets extremely hot.

Video Demo: Boiling Points

Three liquids (oil, isopropyl alcohol, and water) are placed on a hot plate. Over time all of the isopropyl alcohol boils away, half of the water boils, and none of the oil boils. This demonstrates that isopropyl alcohol has the lowest boiling point, followed by water, and oil has the highest boiling point. I show my students this video as we learn about phase change, and the properties of matter (boiling point, melting point, etc.). I ask my students the following questions after the video.

 1. Which liquids boiled?
2. Where did the lost liquids go?
3. The temperatures 78 degrees C, 100 degrees C, and 204 degrees C are the boiling points for the above substances. Match the boiling point temperatures to the substance.
4. Which would hurt more if one of these were to touch your skin: boiling oil or boiling water? Explain.
5. Explain why oil is used to fry foods instead of water (like potatoes, fish, etc.). Hint: look at their boiling points.

Video Demo: Carbon Dioxide Extinguisher

This video demonstrates some of the properties of carbon dioxide gas. Carbon dioxide gas is more dense than air. The gas can be poured kind of like a liquid. The video shows carbon dioxide gas being poured to extinguish a candle flame. A candle flame needs oxygen gas to burn. Since carbon dioxide gas is surrounding the flame, the lack of oxygen gas makes the flame go out. You could also use dry ice as a source of cargon dioxide instead of vinegar and baking soda.

materials needed

large poster board folded

video

Lesson: Rainbow Volume

An important component in learning matter, is being able to measure how much space matter takes up–in other words volume. Measuring the volume of liquids requires the use of a graduated cylinder. Students need practice to use the graduated cylinder effectively. My colleague, Cindy Giove, shared the lab activity, Rainbow Volume with me. It is a fun way for students to practice and an easy way for teachers to assess their growth. Students first start out with beakers of blue, red, and yellow water. They then measure a certain amount of colored water into each test tube. If they follow the directions carefully, and do the measurements accurately they will end up with test tubes with 11 ml of red, orange, yellow, green, blue, and purple water. Download rainbow volume handout. Download rainbow volume key.

Materials: beakers of red, blue, and yellow water, and a 25 ml graduated cylinder

Materials: empty test tubes at the beginning

End results: colors and equal volumes