Given the amount of one reactant, students must use stoichiometry to find the ideal amount of the second reagent to use to create purple fireworks. The teacher ignites each groups' fireworks. Ideal mixture create little or no ash. Student assignment sheet with directions (and different initial amounts) plus teacher information and sample answers are included. This is an exciting and engaging activity that can be used as a stoichiometry quiz.

These worksheets are part of a entire unit on teaching stoichiometry. You can access the complete lesson plans with information on their use, and links to other worksheets, labs, and activities at http://www.jce.divched.org/article/stoichiometry-easy.

Stoichiometry, limiting reactant, laboratory measures

With one balance per table (two groups), the calculations should take about 10 minutes, the measures another 10 minutes. Ideally, students should be prepared to deliver their mixture to the teacher within 20 minutes. In practice, many students will take longer, particularly if the formula for potassium chlorate is not given and students are not familiar enough with ionic nomenclature.

The teacher will need about one minute per group to announce the group's mixture, ignite it, and wait for student responses. So if there are 15 groups, the teacher should allow about 15 minutes to ignite all the mixtures.

**Student materials:**

- 1 - 100 mL beaker
- 1 - 250 mL beaker
- Vial of potassium chlorate (KClO
_{3}) - Vial of sugar (C
_{12}H_{22}O_{11}) - Stirring rod
- Wax pencil
- Centigram balance (ideally one for each lab table).
- goggles

**Teacher Materials:**

- Fireproof board
- Bunsen burner (with long hose)

This experiment is best done in groups of two. Students should have learned how to do stoichiometry problems, be experienced in using a balance, and be able to follow basic directions.

For this lab quiz students are given a specified amount of one reactant (the limiting reactant), and must complete the correct stoichiometry calculation to determine the ideal amount of the other reactant. They are instructed to show all their work.

In a fume hood, the teacher ignites each groups' mixture. Ideally, there are purple flames and sparks and very little white "ash." An excess of sugar results in production of carbon "worms." And excess of potassium chlorate does not burn well and is difficult to ignite.

See the student lab sheet.

See the student lab sheet.

Each table (two groups) needs one balance and one vial of each reagent plus a 100 mL and a 250 mL beaker for each group (two of each beaker). It is convenient to have all the student materials placed in a tub or basket. Each table also should have a centigram balance, if possible. If more than two groups must share a balance, the lab quiz may take more time than is available.

David P. Licata, Pacifica High School, Garden Grove, CA (retired)

## Safety

### General Safety

General Safety

Please refer to the ACS Guidelines for Chemical Laboratory Safety in Secondary Schools (2016). Some additional information on these guidelines can be found in a Pick at ChemEd X.

#### Safety resources

RAMP: Recognize hazards; Assess the risks of hazards; Minimize the risks of hazards; Prepare for emergencies

## NGSS

Matter and its Interactions help students formulate an answer to the question, “How can one explain the structure, properties, and interactions of matter?” The PS1 Disciplinary Core Idea from the NRC Framework is broken down into three subideas: the structure and properties of matter, chemical reactions, and nuclear processes. Students are expected to develop understanding of the substructure of atoms and to provide more mechanistic explanations of the properties of substances. Chemical reactions, including rates of reactions and energy changes, can be understood by students at this level in terms of the collisions of molecules and the rearrangements of atoms. Students are able to use the periodic table as a tool to explain and predict the properties of elements. Using this expanded knowledge of chemical reactions, students are able to explain important biological and geophysical phenomena. Phenomena involving nuclei are also important to understand, as they explain the formation and abundance of the elements, radioactivity, the release of energy from the sun and other stars, and the generation of nuclear power. Students are also able to apply an understanding of the process of optimization in engineering design to chemical reaction systems. The crosscutting concepts of patterns, energy and matter, and stability and change are called out as organizing concepts for these disciplinary core ideas. In the PS1 performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and conducting investigations, using mathematical thinking, and constructing explanations and designing solutions; and to use these practices to demonstrate understanding of the core ideas.

*More information about this category of NGSS can be found at https://www.nextgenscience.org/dci-arrangement/hs-ps1-matter-and-its-interactions.

**"**Matter and its Interactions help students formulate an answer to the question, “How can one explain the structure, properties, and interactions of matter?” The PS1 Disciplinary Core Idea from the NRC Framework is broken down into three subideas: the structure and properties of matter, chemical reactions, and nuclear processes. Students are expected to develop understanding of the substructure of atoms and to provide more mechanistic explanations of the properties of substances. Chemical reactions, including rates of reactions and energy changes, can be understood by students at this level in terms of the collisions of molecules and the rearrangements of atoms. Students are able to use the periodic table as a tool to explain and predict the properties of elements. Using this expanded knowledge of chemical reactions, students are able to explain important biological and geophysical phenomena. Phenomena involving nuclei are also important to understand, as they explain the formation and abundance of the elements, radioactivity, the release of energy from the sun and other stars, and the generation of nuclear power. Students are also able to apply an understanding of the process of optimization in engineering design to chemical reaction systems. The crosscutting concepts of patterns, energy and matter, and stability and change are called out as organizing concepts for these disciplinary core ideas. In the PS1 performance expectations, students are expected to demonstrate proficiency in developing and using models, planning and conducting investigations, using mathematical thinking, and constructing explanations and designing solutions; and to use these practices to demonstrate understanding of the core ideas."

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

*More information about all DCI for HS-PS1 can be found at https://www.nextgenscience.org/dci-arrangement/hs-ps1-matter-and-its-interactions and further resources at https://www.nextgenscience.org.

Students who demonstrate understanding can use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.

Assessment does not include complex chemical reactions.

Emphasis is on using mathematical ideas to communicate the proportional relationships between masses of atoms in the reactants and the products, and the translation of these relationships to the macroscopic scale using the mole as the conversion from the atomic to the macroscopic scale. Emphasis is on assessing students’ use of mathematical thinking and not on memorization and rote application of problem - solving techniques.

## Comments 6

## Exciting

I was immediately thrilled about this Lab Quiz! I am going to do the quiz the last lesson before the Christmas Holidays. Thank you for sharing this!

Maria KraakmanChemistry teacherCartesius LyceumAmsterdam, The Netherlands

## More Stoichiometry items coming

Thanks for the kind comment.

Look for more items, including a specifically Christmas-themed (though algorithmic) aid to learning how to do stoichiometry. Not sure how it will translate into Norwegian, but perhaps your own creativity will find a way to make it work. I am slowly getting my entire stoichiometry unit of worksheets, labs (which are done), collaborative activities, and the Christmas-themed aid uploaded. I am working with the ChemEdX staff to get through some issues with uploading, formatting, and so on, so the work is going slowly. Eventually everything will be linked to a single article that describes the lesson plans I used for nearly 30 years. I hope you will enjoy them.

I hope that you and your students will have fun with this activity. I always promote it several days in advance by telling students that those who do the best will end up with only a small amount of salt, but those who do poorly will be obvious due to the "big ash-sh-sh-sh-sh-huh" that they have -- this takes advantage of the close correspondence in sound between the English word "ash" and the English word for a person's back side. Of course it generates smiles and a few snickers -- and a few more when students see a group that does leave a lot of burnt sugar ash. Again, not sure how that will translate, but we have fun with it.

## Oxidation numbers

This excercise would also be good practice for students to balance redox reactions based on the change in oxidation numbers of C and Cl. On another note, this mixture can also be self-ignited with a small amount of concentrated sulfuric acid but that would undoubtedly also produce some carbonaceous by-product due to the exothermic decomposition of some of the sugar (like in the carbon sausage demo). I wonder if that variation would give similar results (i.e. very little ash except for a tiny bit of carbonaceous by-product produced).

## Stoichiometry quiz

Thank you so much. A good idea which looks like fun and I look forward to using it soon!

Caroline Lehman

## Stoichiometry unit

Thank you so much for your great ideas. I have been teaching for a long while, but am always looking for ideas and ways to improve. As soon as I get a free minute (Christmas break?), I am going to take a closer look at this.

## Take a look over Thanksgiving break

Thanks for the comment. I am sure your students will find the lab fun, and the "competition" exciting. Let me suggest that you take a look at the lab, and my article on how I taught stoichiometry during your Thanksgiving break (well, if you are in the US -- other than turkey and football, you won't have anything else to do, will you??).

The entire article and links to all the other materials I used is at:

http://www.jce.divched.org/article/stoichiometry-easy

You will find more items there, some that you might want to start using before Christmas.

D.