Decomposing Hydrogen Peroxide

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Objective

SWBAT explain that a catalyst enables a chemical reaction.

Big Idea

How is a chemical catalyst like an umpire?

The Need for This Lesson

This lab introduces students to a catalyst. We have seen chemical bonds break when we add heat. In this lesson we will use the energy created by a catalyst to cause a chemical reaction. It is important that students understand that the catalyst can lower the amount of energy required for a chemical reaction and decomposition can occur without the heat from the flame.

This lesson was inspired by a now archived website, Armchair Chemistry*. I have formatted the lab to fit in a journal and modified the text as needed to support the learning of my students.

*Streitberger, Eric. Armchair Chemistry. 2015-02-15. Accessed: 2015-02-15

Investigation Preparation & Summary

10 minutes

Students will look at how a catalyst facilitates a chemical decomposition to break down hydrogen peroxide into its elements. (MS-PS1-1 Develop models to describe the atomic composition of simple molecules and extended structures.)

Students will notice changes in appearance indicating that a chemical reaction has occurred. (MS-PS1-2 Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.)  Questions will be asked to encourage students to analyze their results as they ponder examples of catalyst in sports and their everyday lives. (SP4 Analyzing and Interpreting Data) Their evidence is derived from their careful observations (SP7 - Engaging in Argument from Evidence).

The lesson walks students through the the chemical equation where they see that matter may be changed but mass is conserved. (MS-PS1-5 Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.)

Here is a link to the MSDS for Hydrogen Peroxide should you have lab Material Safety Data Sheet requirements.

Preparation is simple. Students will need small, dime size, samples of an apple, potato, bread and yeast. It is important that the yeast is fresh. Here is the complete materials list

Students in Action

35 minutes

This lesson begins with a Turn/Talk/Record. Students activate prior knowledge by discussing and recording their answers with their elbow partner. In this lesson, I want to be sure that students have some understanding of hydrogen peroxide and how it is commonly used. Students also explore their understanding of a catalyst.

I ask students to stop before they begin the procedure. At that time I ask for student volunteers to share their responses to the questions - An umpire in a baseball game is like a catalyst. Explain how the umpire is a catalyst. Why would some people be called catalysts? Students are able to explain how an umpire or referee is like a catalyst for a sporting event. They are a little unsure about their understanding of people as catalyst. With a little prompting, we explore how people can be a catalyst for change both positive and negative. My students focused on people who spread rumors as catalyst explaining that while the catalyst is not affected by the rumor, they can change the life of others.

The student begin the procedure and I walk around to each table to make sure they are looking closely and making good observations. The bubbles surrounding the apple and the potato are present but sometimes difficult to see unless students are making careful observations. If students do not see the bubbles around the apple and potato, I prompt them to add a bit more hydrogen peroxide and make another observation.

Since we have worked together on the Decomposition of Sucrose and the Decomposition of Copper Sulfate Pentahydrate to fill out the reactant and products table, I encourage students to attempt this one on their own. Students ask clarifying questions as I circulate around the room helping them grapple with thinking like a chemist.

In the student sample, I found that if there were only a few bubbles present, then the student did not answer that the test material was a catalyst. We reviewed the answers during the next class period and made the corrections. The students made the connection between the appearance of bubbles and the identification of a catalyst. 

In this video, I walk through the student sample and explain the strategies behind the format of the student lesson.