Colby College



Crazy About ReactionsTeacher’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: 4-8Estimated Time: 50 minutesPrep Time: 10-15 minutesClean-up Time: 10-15 minutesKey Terms:Chemical reaction- a chemical change that forms a new substanceExothermic reaction- Heat is released when a reaction takes placeEndothermic reaction- Heat is absorbed when a reactions takes placeCatalyst- Helps increase the speed of a reaction but does not undergo a chemical reactionDensity- mass per unit of volumeProcedure: 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.Before the class starts, heat up water and use ice to cool water. It will later be used in the density demonstration.Give the class examples of chemical reactions and ask them to come up with some of their own. 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. 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. Introduce the density demonstration by asking the class what the definition of density is. Ask them if they think it will be possible to keep the two colors of water separated when the bottles are placed on top of each other. 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. 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 ReactionAn 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 cubesMelting saltsEvaporating waterPhotosynthesisCooking an eggBaking bread, cake, etcExothermic ReactionAn 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 cubesBurning a candleMixing water and strong acidsRusting ironFormation of snow in cloudsBurning wood Temperature and DensityCold 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 ReactionsMaterials ListHydrogen peroxide: ? cup per pair Thermometers: 1 per pairMeasuring cupsPaper cups: 1 per pairPlastic cups: 3 per pairMedium size plastic bins: 1 per pairYeast: 1 tablespoon per pairEpsom salt: 1 tablespoon per pairWaterDevice to heat water (microwave, hot plate, electric kettle)Ice to cool waterEmpty soda bottles 16.9 fl oz: 2 per pairFood coloringIndex cards: 1 per pairCrazy About ReactionsStudent’s InstructionsYou 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?3429000116205You will need:Hydrogen peroxideYeastEpsom saltFood coloringThermometerPlastic cupsPaper cupHot waterCold waterRoom temperature waterPlastic soda bottles 16.9 fl ozIndex cardPlastic binProcedure:Part A- Endothermic ReactionPlace 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.Measure 1 tablespoon of Epsom salt and add it to the paper cup. Mix the liquid until the salt has dissolved.Record the temperature with the thermometer every two minutes for a total of ten minutes.Dump out the liquid in the paper cup into the sink.Repeat steps 1-3, but add 2 tablespoons of Epsom salt to the water instead.Record the temperature with the thermometer every two minutes for a total of ten minutes.Write down all observations on your worksheet.Part B- Exothermic ReactionPlace the plastic cup inside of the plastic bin. Measure ? cup of hydrogen peroxide and pour it into the plastic cup. Using the thermometer measure the temperature of the hydrogen peroxide.Measure 1 tablespoon of yeast and add it to the plastic cup.Record the temperature with the thermometer every two minutes for a total of ten minutes.Repeat steps 1-3, but add 2 tablespoons of yeast to the hydrogen peroxide instead.Record the temperature with the thermometer every two minutes for a total of ten minutes.Write down all observations on your worksheet.Part C- Temperature and Density (Demo)Fill one soda bottle with cold water. Add red food coloring to the cold water.Fill the other bottle with hot water (not boiling). Add blue food coloring to the hot water.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.Record your observations on the worksheet.Name: _________________________________________Date: __________________________________________Crazy About ReactionsWorksheet 1Endothermic reaction #1Time Temperature Outside of paper cup0 minutes (before Epsom salt is added)2 minutes4 minutes6 minutes8 minutes10 minutesEndothermic reaction #2Time Temperature Outside of paper cup0 minutes (before Epsom salt is added)2 minutes4 minutes6 minutes8 minutes10 minutesExothermic reaction #1Time Temperature Outside of paper cup0 minutes (before yeast is added)2 minutes4 minutes6 minutes8 minutes10 minutesExothermic reaction #2Time Temperature Outside of paper cup0 minutes (before yeast is added)2 minutes4 minutes6 minutes8 minutes10 minutesName: _________________________________________Date: __________________________________________Temperature and Density DemoColorLocation (circle the answer)Top or bottomTop or bottomName: _________________________________________Date: __________________________________________Crazy About ReactionsWorksheet 2Define terms:Endothermic reaction-Exothermic reaction-Catalyst-Questions:What was added to the water to cause the temperature of the water to decrease?What was added to the hydrogen peroxide to cause the temperature of the hydrogen peroxide to increase?What was the catalyst in the exothermic reaction?Did adding 2 tablespoons of Epsom salt and yeast cause the temperature to change more than when only 1 tablespoon was added?Name: _________________________________________Date: __________________________________________Why did the blue and red water not mix?14859002835275Is hot water more dense or less dense than cold water? Why? ................
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