Summary:

This activity illustrates chemical reactions.  A chemical reaction is just another name for a chemical change.  A chemical change occurs when one or more substances interact to form a new substance with new properties.  This is different from a physical change, which is simply a change in the physical form of a substance – for example, a liquid turning into a gas, a rock being pulverized into tiny pieces.  In a physical change, what the substance is, its chemical identity, does not change.

There are several indications of a chemical reaction.  These include heat transfer, formation of a gas, formation of a solid, color change (sometimes).

Several things happen in this activity. The calcium chloride dissolves and in the process produces heat, so the baggie feels warm, this is a physical change. The baking soda also dissolves, which is also a physical change. Then bicarbonate ions react with calcium ions to make calcium carbonate, a milky white solid. This is a chemical change that produces no heat but does result in an acidic solution, so the cabbage juice turns pink. The acidic protons also react with the bicarbonae ions to make water and carbon dioxide gas, which inflates the bag. This chemical reaction also pulls in heat from the surroundings, so the bag becomes cold as well.

The cabbage juice has two functions in this activity. One is to supply liquid in which to dissolve the solids. The other is to act as an acid-base indicator. Cabbage juice is bluish purple under neutral conditions, pink when acidic, and green when basic.

Reference: http://teachers.net/lessons/posts/108.html, posted by Michael H. Edmondson, Hardaway High School

Learning Goals / Objectives:

Relevant California 3th grade Science Standards
Physical Science 1g: Students know that when two or more substances are combined, a new substance may be formed with properties that are different from those of the original materials.

Relevant California 5th grade Science Standards
Physical Science 1a: Students know that during chemical reactions the atoms in the reactants rearrange to form products with different properties.

Relevant California 8th grade Science Standards
Physical Science 5a: Students know reactant atoms and molecules interact to form products with different chemical properties.

Relevant California HS Science Standards: Chemistry
2.Biological, chemical, and physical properties of matter result from the ability of atoms to form bonds from electrostatic forces between electrons and protons and between atoms and molecules.

Learning Objectives
1. When two or more substances come together to produce a new and different product, a chemical reaction has occurred.
2. Chemical reactions result in the production of new substances with different properties.
3. A color change can signify a chemical reaction.
4. Formation of a solid is another sign of a chemical reaction.

Background

Setup:

Have all materials out and clearly labeled for students to easily find.

Anticipatory Set:

Discuss chemical reactions with the students prior to this activity, focusing on the evidence of a chemical reaction that they should be looking for. Also discuss how to record their observaions.

Instructions / Activities:

• Measure out 2 teaspoons of the solid calcium chloride into the Ziploc baggie. Write down your observations about this solid.
• Measure out 1 teaspoon of the baking soda into the same baggie, sliding all the solids together into one corner of the baggie. Write down your observations about this solid.
• Put about 10 mL of the cabbage juice into a vial and place this, without a lid, into the opposite corner of the baggie. Write down your observations about this liquid.
• Force all the air out of the baggies and zip it closed. Tip over the vial to spill the cabbage juice onto the solids. Mix well with your hands.
• Observe what happens and write down all your observations. Make sure to write down what you feel as well as what you see.

Assessment:

1. Do you think a reaction occurred when you added the two solids together? Why or why not? List all of your reasons.

2. Do you think a reaction occurred when you tipped the liquid into the solids? Why or why not? List all of your reasons.

3. Do you have evidence of the formation of a new and different product after you mixed the liquid and solids? If so, what is that evidence? If not, what do you think happened here?

Wrap-up / Closure:

Explain to the students what was happening, going over each step explained in the summary.

Attachments: