Investigate Chemical Changes - What are some signs of chemical change?

Jeanine Salisbury, Robbinsdale Middle School, Robbinsdale, MN based on an original activity from McDougal Littell Science, Matter and Energy p.47
Author Profile

Summary

This is an open inquiry lab that can be done in approximately 15-20 minutes with a few household materials. It dramatically, yet simply, illustrates the condition of color change and the formation of gas (bubbles) as a result of a chemical change.

Learning Goals

Skills:
1. Following step by step written instructions
2. Following a sequence
3. Measuring
4. Working collaboratively
5.Recording observations
Thinking Skills:
1. Knowledge and comprehension.
2. Synthesis and evaluation.
3. Metacognition.

Key Concepts:

There are five signs of a chemical change:
1. Color Change
2. Production of an odor
3. Change of Temperature
4. Evolution of a gas (formation of bubbles)
5. Precipitate (formation of a solid)

Vocabulary:
1.Chemical properties
2. Chemical change
3.Precipitate

Context for Use

This activity would be appropriate for just a few students up to as many as 30-35. The only limitation would be desk space and graduated cylinders. Everything else can be obtained from a grocery store. The lab is inquiry and it can be used to introduce the concepts of chemical change. It can also be used to demonstrate the chemical changes of color and bubbles. It is a lab that takes approximatelu 15-20 minutes of class time to do. It will also require 15-20 minutes for recording observations and answering questions, as well as additional time for set up and clean up. The time required for these, would depend on the number of children doing the lab. It can be done individually or in groups of two. If necessary, it can be done with larger groups, but it is much more fun with 1 or two students. The only special equipment that will be needed are graduated cylinders. It is helpful if students have studied physical changes, but not necessary. This lab can be used as an anticipatory set, or as an example(s) of chemical changes in materials. The children can do the lab and then learn why the changes took place, or they can use it to demonstrate learned concepts. This activity can be used in most any setting.

Subject: Chemistry:General Chemistry
Resource Type: Activities:Lab Activity
Grade Level: Middle (6-8)

Description and Teaching Materials

Materials required for 1 experiment:
1. 1 graduated cylinder
2. Water
3. 2 clear plastic cups
4. 2 eyedroppers
5. Iodine or Lugol's solution
6. Cornstarch
7. 2 spoons (plastic)
8. 1 vitamin C tablet

Procedure:
1.Measure 80mL of water and pour it into one of the cups.
2. Add three full droppers of iodine solution. Record your observations.
3. Add one spoonful of cornstarch to the iodine solution and stir. Record your observations.
4.Measure 50 mL of water and pour it into the second cup.
5. Using a clean eyedropper, add 4 full droppers of the iodine/cornstarch solution to the second cup.
6. Drop a vitamin C tablet into the second cup and stir the liquid with a clean spoon until the tablet is dissolved. Record your observations.

What do you think?
1. What changes did you observe in the first cup? In the second cup?
2. Do you think that chemical changes occurred? Why or why not.
3. What are some characteristics of chemical changes? Can you list all five?
Challenge: Describe some chemical changes that you have seen take place in your home or school.

Reference:
McDougal Littell Science, Matter and Energy, Copyright 2005, McDougal Littell, a division of Houghton Mifflin Company, pg. 47

Teaching Notes and Tips

Tips: You can use iodine from any drug store. Just be careful as it stains and probably will not come out of clothing. Old adult male shirts work well as lab coats and can be obtained at thrift stores very reasonably. If you use Lugol's solution, add enough to make the solution dark yellow/orange. Plain iodine will be dark red.
If Vitamin C tablets are used, crush them first and they will dissolve faster. If you do not have Vitamin C tablets, orange or lemon juice works as well.
Possible Answers to What do you Think?
The color changed from yellow/orange, red to blue-black in the first cup. In the second cup, the color changed and bubbles formed. Yes; new substances formed, as evidenced by the color changes and bubbles. Some signs of a chemical change are a change in color and the formation of bubbles. The five conditions of chemical change: color change, formation of a precipitate, formation of a gas, odor change, temperature change.
Challenge: food cooking, rust formation, tarnish forming on doorknobs, fuel burning for heat, tarnished penny.

Assessment

The assessment can be either formal or informal. The students can write the answers to the questions in their science journals, or on a piece of paper to turn in. They can also talk about their observations in small groups or large class discussions.

Standards

1) 6.I.A.1 The student will distinguish between scientific evidence and personal opinion.
2) 6.I.A.4 The student will define scientific facts, laws and theories.
3. 6.I.B.2 the student will distinguish among observation, prediction and inference.
4. 6.II.B.1. The student will define chemical and physical changes.
5. 6.II.B.2 The student will observe that substances react chemically with other substances to form new substances with different characteristic properties.