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Crazy About Reactions

Teacher’s Instructions

Teaching Objectives:

  • Students will learn about chemical reactions.
  • Students will conduct their own endothermic and exothermic reactions.
  • Students will observe the effects of temperature on density.

Recommended Grades: 4-8

Estimated Time:50 minutes

Prep Time:10-15 minutes

Clean-up Time:10-15 minutes

Key Terms:

Chemical reaction-a chemical change that forms a new substance

Exothermic reaction- Heat is released when a reaction takes place

Endothermic reaction- Heat is absorbed when a reactions takes place

Catalyst- Helps increase the speed of a reaction but does not undergo a chemical reaction

Density-mass per unit of volume

Procedure:

  1. Pair up the students. Each pair will conduct both reactions. In front of each pair, place 1 paper cup, 2 plastic cups, 1 plastic bin, thermometer, measuring cups, room temperature water, bottle of hydrogen peroxide, and a bag of Epsom salt and yeast. If the students are grades 5-8 allow them to measure every ingredient on their own.. If the students are grades K-4, pre-measure all ingredients. Make sure to label all plastic bags or containers so the students know what everything is. By pre-measuring the ingredients, you will minimize some of the mess.
  2. Before the class starts, heat up water and use ice to cool water. It will later be used in the density demonstration.
  3. Give the class examples of chemical reactions and ask them to come up with some of their own.
  1. Start with the endothermic reaction. Ask the students predict what will happen to the temperature of the water when Epsom salt is added to it. Then let them carry out the experiment. Remind them to record all of the data and their observations on worksheet 1.
  2. Next, have the students perform the exothermic reaction. Ask the students predict what will happen to the temperature of the hydrogen peroxide when yeast is added to it.
  3. Introduce the density demonstration by asking the class what the definition of density is. Ask themif they think it will be possible to keep the two colors of water separated when the bottles are placed on top of each other.
  4. Make sure to conduct this demonstration in a plastic bin because some of the blue water might spill. Make sure the water is not too hot because the blue water is hot and tends to spill. This demonstration will require two people.
  5. After the demonstration ask the students why the colors did not mix. Tell them about the effects of temperature on the density of water.

How it works:

Endothermic Reaction

An endothermic reaction is a chemical reaction that requires heat in order to occur. This means that heat is absorbed from the surrounding areas. For this experiment, the Epsom salt is absorbing the heat from the water, thus causing the temperature of the water to decrease.

Examples:

Melting ice cubes

Melting salts

Evaporating water

Photosynthesis

Cooking an egg

Baking bread, cake, etc

Exothermic Reaction

An exothermic reaction is a chemical reaction that releases heat. For this experiment, the hydrogen peroxide undergoes a decomposition reaction. This means that the hydrogen peroxide breaks down into different components, oxygen gas (bubbles) and water. Heat is also a product of the decomposition reaction. The yeast acts as a catalyst, which means that it helps increase the rate of the decomposition (breakdown) of the hydrogen peroxide, but itself does not undergo any chemical change.

Examples:

Process of making table salt (NaCl)

Making ice cubes

Burning a candle

Mixing water and strong acids

Rusting iron

Formation of snow in clouds

Burning wood

Temperature and Density

Cold liquids are denser than hot liquids. In cold liquids, the molecules move around less because they have less energy to move around. This means that the molecules are packed closer together. Another way to look at it is that more molecules in a cold liquid are able to pack in the same total volume than the molecules in a hot liquid. Hot liquids are less dense so it will float on top of the cold water instead of mixing with the cold water. The colored water will eventually mix together once they both reach the same temperature.

References:

Bardhan-Quallen, Sudipta. Championship Science Fair Projects: 100 Sure-to-Win Experiments. Scholastic Inc: New York. 2005.

Water Density Experiment. (accessed January 9, 2012).

Crazy About Reactions

Materials List

  • Hydrogen peroxide: ¼ cup per pair
  • Thermometers: 1 per pair
  • Measuring cups
  • Paper cups: 1 per pair
  • Plastic cups: 3 per pair
  • Medium size plastic bins: 1 per pair
  • Yeast: 1 tablespoon per pair
  • Epsom salt: 1 tablespoon per pair
  • Water
  • Device to heat water (microwave, hot plate, electric kettle)
  • Ice to cool water
  • Empty soda bottles 16.9 fl oz: 2 per pair
  • Food coloring
  • Index cards: 1 per pair

Crazy About Reactions

Student’s Instructions

You have entered into a science competition. There are three criteria: you have to make a liquid colder, make a liquid hotter, and prevent two different colors of water from mixing when put together. Are you up for the challenge?

You will need:

  • Hydrogen peroxide
  • Yeast
  • Epsom salt
  • Food coloring
  • Thermometer
  • Plastic cups
  • Paper cup
  • Hot water
  • Cold water
  • Room temperature water
  • Plastic soda bottles 16.9 fl oz
  • Index card
  • Plastic bin

Procedure:

Part A- Endothermic Reaction

  1. Place the paper cup inside of the plastic bin. Fill the paper cup half way with room temperature water. Using the thermometer measure the temperature of the water.
  2. Measure 1 tablespoon of Epsom salt and add it to the paper cup. Mix the liquid until the salt has dissolved.
  3. Record the temperature with the thermometer every two minutes for a total of ten minutes.
  4. Dump out the liquid in the paper cup into the sink.
  5. Repeat steps 1-3, but add 2 tablespoons of Epsom salt to the water instead.
  6. Record the temperature with the thermometer every two minutes for a total of ten minutes.
  7. Write down all observations on your worksheet.

Part B- Exothermic Reaction

  1. Place the plastic cup inside of the plastic bin.
  2. Measure ¼ cup of hydrogen peroxide and pour it into the plastic cup. Using the thermometer measure the temperature of the hydrogen peroxide.
  3. Measure 1 tablespoon of yeast and add it to the plastic cup.
  4. Record the temperature with the thermometer every two minutes for a total of ten minutes.
  5. Repeat steps 1-3, but add 2 tablespoons of yeast to the hydrogen peroxide instead.
  6. Record the temperature with the thermometer every two minutes for a total of ten minutes.
  7. Write down all observations on your worksheet.

Part C- Temperature and Density (Demo)

  1. Fill one soda bottle with cold water. Add red food coloring to the cold water.
  2. Fill the other bottle with hot water (not boiling). Add blue food coloring to the hot water.
  3. Before inverting the bottle place everything in a plastic bin because the blue water will spill. Using an index card, invert the blue soda bottle. Line up the openings with the red soda bottle. Once it is aligned, carefully remove the index card.
  4. Record your observations on the worksheet.

Name: ______

Date: ______

Crazy About Reactions

Worksheet 1

Endothermic reaction #1

Time / Temperature / Outside of paper cup
0 minutes (before Epsom salt is added)
2 minutes
4 minutes
6 minutes
8 minutes
10 minutes

Endothermic reaction #2

Time / Temperature / Outside of paper cup
0 minutes (before Epsom salt is added)
2 minutes
4 minutes
6 minutes
8 minutes
10 minutes

Exothermic reaction #1

Time / Temperature / Outside of paper cup
0 minutes (before yeast is added)
2 minutes
4 minutes
6 minutes
8 minutes
10 minutes

Exothermic reaction #2

Time / Temperature / Outside of paper cup
0 minutes (before yeast is added)
2 minutes
4 minutes
6 minutes
8 minutes
10 minutes

Name: ______

Date: ______

Temperature and Density Demo

Color / Location (circle the answer)
Top or bottom
Top or bottom

Name: ______

Date: ______

Crazy About Reactions

Worksheet 2

Define terms:

Endothermic reaction-

Exothermic reaction-

Catalyst-

Questions:

  1. What was added to the water to cause the temperature of the water to decrease?
  1. What was added to the hydrogen peroxide to cause the temperature of the hydrogen peroxide to increase?
  1. What was the catalyst in the exothermic reaction?
  1. Did adding 2 tablespoons of Epsom salt and yeast cause the temperature to change more than when only 1 tablespoon was added?

Name: ______

Date: ______

  1. Why did the blue and red water not mix?
  1. Is hot water more dense or less dense than cold water? Why?

Kimi Kossler

January 2012