Summary

In this demonstration, students observe a series of teacher led demonstrations to learn how to identify evidence that a chemical reaction has occurred, how to write a word equation to explain a chemical reaction, and how to convert a word equation to a balanced chemical equation.

Grade Level

High School and Middle School

NGSS Alignment

This demonstration will help prepare your students to meet the performance expectations in the following standards:

• Scientific and Engineering Practices:
  • Analyzing and Interpreting Data

Objectives

By the end of this demonstration, students should be able to

• Identify evidence that a chemical reaction has occurred.
• Know the five indicators that a chemical reaction has occurred.
• Write a word equation to explain a chemical reaction.
• Convert a word equation to a balanced chemical equation.

Chemistry Topics

This demonstration supports students’ understanding of

• Chemical Reactions
• Chemical Change
• Indicators of Chemical Reactions
• Conservation of Mass
• Balancing Equations

Time

Teacher Preparation: 30-45 minutes

Lesson: 60 minutes

Materials

Demonstration 1:

• 1 test tube
• Forceps
• 1M hydrochloric acid, HCl
• Copper (Cu) metal granules

Demonstration 2:

• 1 test tube
• Forceps
• 1M hydrochloric acid, HCl
• Zinc (Zn) metal granules

Demonstration 3:

• 2 test tubes
• Solution of potassium iodide, KI
• Solution of lead (II) nitrate, Pb(NO₃)₂

Demonstration 4:

• 2 test tubes
• Solution of potassium thiocyanate, KSCN
• Solution of iron (III) nitrate, Fe(NO₃)₃

Demonstration 5:

• 2 test tubes
• Solution of potassium iodide, KI
• Aluminum nitrate, Al(NO₃)₃

Demonstration 6:

• Large beaker (minimum 1000 ml)
• Wire gauze
• Ethanol
• Paper towel
• Wooden splint
• Matches
• Ammonium dichromate, (NH₄)₂Cr₂O₇

Demonstration 7:

• Beaker tongs
• Bunsen burner
• Magnesium ribbon, Mg

Safety

• Wear protective gloves, clothing and eyewear for all demonstrations.
• Wash hands thoroughly after handling chemicals.
• Students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Only use hydrochloric acid, HCl, in a hood or well-ventilated area.
• Only use lead (II) nitrate, Pb(NO₃)₂, in a hood or well-ventilated area.
• Ammonium dichromate, (NH₄)₂Cr₂O₇, is toxic; use only in a hood or in well ventilated area.
• Avoid looking directly at burning magnesium.

Teacher Notes

• For more information about these demonstrations, read the associated article, My Favorite Demonstrations for Teaching Chemical Reactions, published in the May 2019 issue of Chemistry Solutions.
• To transition easily from one demonstration to the next, I set up the materials for the seven demonstrations in the following manner:
  • Demonstrations 1 and 2: I place the 1M hydrochloric acid in a test tube, and each metal sample in a beaker.
  • Demonstrations 3, 4, and 5: I place one of the aqueous solutions in a test tube and the other solution in a dropper bottle. Alternatively, both reactants can be placed in test tubes.
  • Demonstration 6: I place ammonium dichromate in a 1000 mL beaker (or larger) with wire gauze over the opening. Since it will be ignited, I also create a wick using a small piece of paper towel soaked in ethanol. I use tongs to place the wick on top of the ammonium dichromate (like placing a candle into a birthday cake) and then use a burning wooden splint to light the wick.
  • Demonstration 7: I place a precut magnesium ribbon in a beaker.
• I use a document camera to display each demonstration, which is connected to a classroom Smart Board, allowing all students to easily see the details of the reactions as they occur. Additionally, this serves as a helpful way to display the written information from the student handout next to the results.
• During the demonstrations, I compile and record information shared by my students in the data table displayed using the document camera and Smart Board.
• Before beginning a reaction, I have my students describe the appearance of the reactant(s) in the data table provided on the student handout. I direct them to record details about color, physical state, texture of the reactants, etc.
• I perform these demonstrations in the following order:

1. Copper metal granules are added to 1M hydrochloric acid.
2. Zinc metal granules are added to 1M hydrochloric acid.
3. Aqueous solutions of potassium iodide and lead (II) nitrate are combined.
4. Aqueous solutions of potassium thiocyanate and iron (III) nitrate are combined.
5. Aqueous solutions of potassium iodide and aluminum nitrate are combined.
6. Ammonium dichromate is ignited.
7. Magnesium ribbon is ignited.

• Demonstration Procedures:
  • *Note that quantities are not indicated in the procedure, as specific amounts are not necessary. Small scale-reactions should be performed by the teacher.

• An answer key document has been included, and is available for download. Some additional information to be aware of for teachers:
  • Demonstrations 1 and 5 will not produce a chemical reaction.
  • Five of the reactions will produce indicators of a chemical reaction for students to observe.
  • Demonstration 2, students will observe the formation of gas, as bubbles are produced when zinc metal is added to a test tube containing 1M hydrochloric acid. Additionally, they will notice the change in color of the zinc metal.
  • Students should note gas formation in several of the demonstrations, including Demonstrations 2 and 6.
  • Demonstrations 3, 4, and 6 will each show a distinctive color change.
  • Demonstration 3 will produce a precipitate.
  • Students will notice light is produced in Demonstrations 6 and 7.
• After all seven demonstrations have been completed, I work with students to develop word equations for any demonstrations that resulted in a chemical reaction.
• The final component of the activity is for students to create formula equations. I typically assist students with the equation for demonstration 2 and allow the students to complete the other equations on their own. I use this time to move around the classroom and provide individualized help to students.