Rainbow in a Bag Exploration

Every kind of matter in our world is a mixture, an element or a chemical compound. Each of these kinds of matter has its own set of physical and chemical properties by which it can be identified.

A chemical change is a change in the nature of a substance. When a chemical compound undergoes a reaction, it changes in identity. The physical properties of the reacting compound are replaced by the physical properties of the product. For this reason, observing a physical change often indicates that a chemical change has occurred. Some physical changes that signal a chemical change are a color change, formation of bubbles, a change in crystal form, disappearance of a solid, or change in temperature. 

Purpose: To observe physical properties of CaCl₂ (calcium chloride) and NaHCO₃ (sodium bicarbonate) and relate them to chemical changes.

Question: What is the effect of combining CaCl_2, NaHCO₃ and universal indicator on the physical properties of the substances?

Hypothesis:

Procedure:

• Put two scoops of CaCl₂ and NaHCO₃ (baking soda) in a zip lock bag.

• Close the bag. Mix contents and record observations. What physical properties of each reactant do you see? Record in the table below. These will become your experimental control or standard to compare against.

• Fill a test tube half way with universal indicator.

• Place the test tube of indicator solution upright into the zip lock bag. Zip bag tightly closed.

• Tip test tube over to spill the indicator solution into the white powder mixture. Mix and record your observations. What physical properties do you see? Have they changed from your experimental control.

Observations: (also include labeled drawings of both before and after)
             CaCl₂       +            NaHCO₃       +      Universal Indicator  →      Products

Before Labeled Drawing:                                After Labeled Drawing:

Analysis Questions:

1.Did a chemical change occur? How do you know?

2. What can you infer from your observations about the substances remaining after the indicator solution was mixed with CaCl₂ and NaHCO₃?

3. Do bubbles always indicate the occurrence of a chemical change? Explain why or why not?

4. Explain the physical and chemical changes that occur when gasoline enters an automobile engine and burns.