Through simple lessons involving a balloon and a pretzel, students learn about simple chemical and physical changes, and the difference between the two.

Students will understand the characteristics of simple chemical and physical changes in foods.

• Students will follow directions on the worksheets.

• Students will discover what physical and chemical changes occur to the balloons and the pretzels.

• Students will write their reflections to the questions concerning physical and chemical changes.

Ohio Academic Content Standards

Physical Sciences
Benchmark A:
Compare the characteristics of simple physical and chemical change.

Indicators:
Nature of Science: Grade 4
1. Identify characteristics of simply physical change.

2. Identify characteristics of simple chemical change.Scientific Inquiry

Benchmark C:
Use appropriate instruments safely to observe measure and collect data when conducting a scientific investigation.

Benchmark C:
Develop, design and safely conduct scientific investigations and communicate the results.

Indicators:
Doing Scientific Inquiry: Grade 3
1. Select the appropriate tools and use relevant safety procedures to measure and record length and weight in metric and English units.

2. Discuss observations and measurements made by other people.

3. Read and interpret simple tables and graphs produced by self/others.

5. Record and organize observations (e.g., journals, charts and tables).

6. Communicate scientific findings to others through a variety of methods (e.g., pictures, written, oral and recorded observations).

Doing Scientific Inquiry: Grade 4
1. Select the appropriate tools and use relevant safety procedures to measure and record length, weight, volume, temperature and area in metric and English units.

3. Develop, design and conduct safe, simple investigations or experiments to answer questions.

4. Explain the importance of keeping conditions the same in an experiment.

5. Describe how comparisons may not be fair when some conditions are not kept the same between experiments.

6. Formulate instructions and communicate data in a manner that allows others to understand and repeat an investigation or experiment.

Materials

• Balloons

• Stick pretzels

• Napkins

• Magnifying glass

• Scale

• Linear measuring tool

Optional Items for Extension

• Gum

• Water

• Vinegar

• Baking soda

Procedure

Lesson 1

1. Distribute Physical Changes worksheet and discuss vocabulary and background information.

2. Follow the direction on the worksheet together. Be sure to stop and discuss student answers about the changes in the balloon.

Lesson 2

1. Distribute Chemical and Physical Changes worksheet and pretzels.

2. After students have drawn their pictures of a pretzel, discuss the term “quantitative observations” (how big, small, heavy, long, etc.). As students measure their pretzels in Part 1, determine as a class which way to hold the pretzel to measure its length, width and height.

3. Discuss the term “qualitative observations” (using your senses). As students describe the properties of their pretzels, record this information on the board. NOTE: Do not let students taste their pretzels at this point. They will do this during Step 4.

4. Work through Step 4 together. Some students may be reluctant to take the chewed pretzel out of their mouths to look at it on a napkin. If so, have them mash a pretzel into small pieces and mix it with a small amount of water.

5. On their own, have students complete the reflection section. Share these answers at a later time.

Evaluation

Students will be evaluated on the individual work during these two experiments and how well they performed on the reflection. Use the included rubric for evaluation.

Background Information

Physical Changes
When you jump into a swimming pool, your swimsuit gets wet but it’s still a swimsuit. If you break a glass, you change its shape but the pieces are still glass. If you freeze water into ice cubes, you change its state of matter but it is still just water. When you change an object’s state of matter, the change can be reversed. For example, water (liquid) that changes to ice (solid) can be changed back into water. It can also be changed to steam (gas) and back into water again.

Chemical Changes
When two or more materials combine to make a new material, the new material has chemical properties that are different from the original materials. When you burn a piece of paper, you’ve added fire to the original material, which changes the paper into ashes. This procedure cannot be reversed in order to change the ashes back into paper. When you mix vinegar and baking soda you get a chemical reaction. The two materials combine together to make a new substance that cannot be separated to form its original parts. When you take a bite of a pretzel, saliva from your mouth begins mixing with the pretzel in order to “break down” the pretzel for your body to digest. This process cannot be reversed in order to return the pretzel back to its original form.

Answers for Extension Questions

Question 1.

B. The smell and color change of the rotting potato

 

Question 2. Which of the following actions causes only a physical change and not a chemical change?

A. Tearing a tissue paper

 

Rubric: Chemical and Physical Changes