Basic Chemistry in a Bag

Investigating Endothermic and Exothermic Chemical Reactions

Feb 25, 2009 David R. Wetzel

Students investigate chemical reactions in a two part inquiry-based investigation designed to allow students make connections with a variety of chemical reactions.

Chemical reactions result in the release of energy in the form of heat, light, or sound. When chemical reactions occur something new is created as a result of the reaction. This evidence can be observed in the form of a change in color, rust, change in temperature, and production of a gas. This investigation is designed for grades 4-8.

This investigation follows the principles of problem solving and use of science process skills as students investigate the two main types of chemical reactions – endothermic and exothermic. Endothermic chemical reactions result in the absorption of energy and exothermic reactions result in the release of energy.

• Endothermic reactions are evidenced by a drop in temperature. One example is the drop in temperature when you activate the ingredients in a first aid kit cold pack.

• Exothermic reactions are evidenced by an increase in temperature. One example is when a match is lit, temperature increases and light is produced.

These two investigations use safe materials that do not require any special disposal requirements.

Materials (per group)

• Large resealable plastic bag to hold all materials
• Piece of steel wool
• Small thermometer
• Small jar with lid containing vinegar (small baby food jar)
• Tall jar with lid
• Small Styrofoam cup
• 25 ml of citric acid solution
• 15 g of baking soda
• Stop watch
• Graph paper
• Stirring rod
• Elastic gloves
• Paper towels
• Safety goggles (not part of bag)

Procedures

Part 1 – Endothermic Reaction

1. Pour the citric acid solution in a Styrofoam cup. Use a thermometer to record the initial temperature.
2. Stir in the baking soda (sodium bicarbonate). Track the change in temperature over a period of 10 minutes observing temperature changes.
3. Record your group’s observations of the chemical reaction(s), graph changes in temperature, and evidence to support your conclusions.

Part 2 – Exothermic Reaction

1. Place the thermometer in the tall jar and close the lid. Allow 5 minutes for the thermometer to record the temperature inside the jar.
2. Next open the lid and remove the thermometer. Record the temperature.
3. Place the piece of steel wool in jar with vinegar and soak for 1 minute.
4. Put on elastic gloves and squeeze the excess vinegar out of the steel wool.
5. Wrap the steel wool around the thermometer and place in the tall jar, closing the lid.
6. Allow 5 minutes, then read the temperature and compare it with the first reading.
7. Record your group’s observations of the chemical reaction(s), along with evidence to support your conclusions.

Teacher Notes

Part 1

1. The Styrofoam cup acts as an insulator from surrounding surfaces and air.
2. Extension – vary the concentrations of citric acid solution and baking soda.

Part 2

1. The vinegar removes the protective coating on the steel wool and once the coating is removed oxidation of the iron in the steel wool produces rust.
2. Extension – vary the size of the steel wool and time soaking in vinegar.

Student Questions

1. What type of chemical reaction took place and what evidence do you have to support your answer in Part 1?
2. What was the change in temperature your group recorded in Part 1?
3. What other examples of this type of chemical reaction have you observed before in Part 1?
4. What type of chemical reaction took place and what evidence do you have to support your answer in Part 2?
5. What other examples of this type of chemical reaction have you observed before in Part 2?

Additional ideas for asking students questions can be found in twenty questions to ask students in science projects.

Making Connections

Students develop a greater understanding of the types of chemical reactions as they complete this inquiry-based investigation. Understanding the basics of chemical reactions is important for making connections with other examples; such as photosynthesis (endothermic), melting ice (endothermic), erupting volcano (exothermic), global warming (exothermic), along with many more examples.

As students develop a greater understanding of scientific inquiry, they learn to ask tougher questions and apply critical thinking skills. They develop the skills necessary to make detailed observations and draw more informed conclusions based on evidence they collect.

The copyright of the article Basic Chemistry in a Bag in Curricula/Lesson Plans is owned by David R. Wetzel. Permission to republish Basic Chemistry in a Bag in print or online must be granted by the author in writing.

Chemical Reaction

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