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Notes for teachers

This activity is best done as a culmination activity toward the end of your instruction on reaction rates. Students should have a foundational understanding of factors that affect reaction rates before they begin.

Hydrogen peroxide (H₂O₂) is a reactive molecule that readily decomposes into water (H₂O) and oxygen:�� 2H₂O₂ --> 2H₂O + O₂(g)�� In this demonstration, sodium iodide catalyzes the decomposition so that it proceeds much more rapidly than normal. The dishwashing detergent captures the oxygen that is released, making foam. Food coloring can color the film of the bubbles so that you get colored foam. In addition to being a nice example of a decomposition reaction and a catalyzed reaction, the elephant toothpaste reaction is exothermic, so heat is produced.

List of Materials

graduated cylinder
metal pan
dish soap
hydrogen peroxide solution 3%
hydrogen peroxide solution 15%
hydrogen peroxide solution 30%
Sodium Iodine solution
dropper
food coloring (optional)

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Standards

Arizona State Standard

HS.P1U1.3 Ask questions, plan, and carry out investigations to explore the cause and effect relationship between reaction rate

factors.

Science and Engineering Practices

Planning and carry out investigations

Obtaining, evaluating and communicating

evidence

Disciplinary Core Ideas

All matter in the Universe is made of very small particles.

Chemical processes, their rates, and whether or not energy is stored or released can be understood in terms of the collisions of molecules and the rearrangements of atoms into new molecules, that are matched by changes in kinetic energy.

Standards

Cross Cutting Concept

Causes and effect

Next Generation Science Standards

HS-PS1-5.

Apply scientific principles and evidence to provide an explanation about the effects of changing the temperature or concentration of the reacting particles on the rate at which a reaction occurs.

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Objectives:

1.Study chemical changes how hydrogen peroxide changes into oxygen and water vapors.

2. Consider how concentration and the presence of a catalyst affect the reaction rate.

3. Design and conduct a scientific investigation.

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Agenda

Duration : one hour to an hour and a half (depending on whether you want to do post lab as homework)

Prelab: 15 minutes to review key concepts, definitions and safety concerns

Laboratory: 35 minutes to complete the detailed procedures

Graphing: 10 minutes for students to use graphing software to complete and attach graphs to laboratory report

Post lab: 30 minutes to complete

conclusion questions

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Intro/Driving Question/Opening

Driving Question

To determine the effect of reactant concentration and addition of a catalyst on the rate of a chemical reaction.

Background information: The reaction you will be completing today is the decomposition reaction: 2 H₂O₂ → 2 H₂O + 1 O₂.

The addition of dish soap is used to trap the O₂ and create the foam.

Review Prelab, definitions and safety concerns before beginning the laboratory activity

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Hands-on Activity Instructions

Groups of 3-4 student work well for this activity

Place your graduated cylinder into the metal pan on your bench. The experiment MUST be completed inside the pans to contain the mess.
Place 1.5 mL of dish soap (one dropper full) into the bottom of your 100 mL graduated cylinder.
Add 10 mL of 3.0% H₂O₂ into the graduated cylinder. Be very careful with H₂O₂ because it is highly corrosive and can cause white burns.
Time the rate of the reaction and the volume of foam produced with each concentration of H₂O₂
Document your findings in the data table.
Wash out your graduated cylinder and repeat steps 1-4 with 15% and 30% hydrogen peroxide.

Addition of a Catalyst

Repeat steps 1-6 with the addition of 5 drops of sodium iodide to each of the setups.

Student Sheet

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Assessment

Component of the Lab Report	Point Value	0	1	2	3	4
Introduction (Asking Questions)		Unable to complete with support given	Extra support needed	Some support needed	Minimal support needed	Students ask specific questions. Students’ questions are scientific and testable. (i.e., answerable through gathering quantitative or qualitative evidence about the natural world to determine relationship between variables.)
Investigation (Planning an Investigation)		Unable to complete with support given	Extra support needed	Some support needed	Minimal support needed	Students design and conduct investigations that will gather relevant data to answer the empirical question. Students make decisions about experimental variables, controls, and investigational methods (e.g., number of trials) that will produce accurate and reliable data.
Investigation (Carrying out an Investigation)		Unable to complete with support given	Extra support needed	Some support needed	Minimal support needed	Students carry out investigations with replicable procedures, using appropriate tools, trials, and safety procedures. The student takes full and relevant data/observations, and when possible manipulates variables to ensure the most valid investigation possible.
Analysis and Conclusion (Obtaining, Evaluating, and Communicating Information)		Unable to complete with support given	Extra support needed	Some support needed	Minimal support needed	Students read and evaluate text from multiple resources to independently obtain scientific information. Students produce scientific writing, or presentations that accurately communicate these ideas, using evidence and rationale for the implications. Students consider the validity and reliability of claims, methods, and designs, verifying the data when possible.
Total Score		Notes:

Reaction Rates

Science Investigation Rubric

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Differentiation

Circulating as groups work on their data collection and analysis of their results will allow the teacher to provide additional assistance to groups that may need it. This might include inspecting tables to make sure data quality will yield good results and that students have any necessary support while working through graphing operations in the chosen application

For issues that perplex multiple groups, a whole-class discussion can help, especially if suggestions for solutions come from the other groups in the classroom instead of the teacher.

Remediation

Extension/Enrichment

Groups that complete their analysis quickly can be enlisted to assist those that might be struggling, especially with the nuts and bolts of collecting and analyzing data. Teaching others is always the best way to become expert in something new.

If time and materials all student can try the experiment with differently-shaped containers. What happens if you use a bottle with a narrower or wider neck, or a cylindrical drinking glass with no neck?

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